.so man3/malloc.3 .\" copyright (c) 2008 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th makedev 3 2021-03-22 "linux" "linux programmer's manual" .sh name makedev, major, minor \- manage a device number .sh synopsis .nf .b #include .pp .bi "dev_t makedev(unsigned int " maj ", unsigned int " min ); .pp .bi "unsigned int major(dev_t " dev ); .bi "unsigned int minor(dev_t " dev ); .fi .sh description a device id consists of two parts: a major id, identifying the class of the device, and a minor id, identifying a specific instance of a device in that class. a device id is represented using the type .ir dev_t . .pp given major and minor device ids, .br makedev () combines these to produce a device id, returned as the function result. this device id can be given to .br mknod (2), for example. .pp the .br major () and .br minor () functions perform the converse task: given a device id, they return, respectively, the major and minor components. these macros can be useful to, for example, decompose the device ids in the structure returned by .br stat (2). .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br makedev (), .br major (), .br minor () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to the .br makedev (), .br major (), and .br minor () functions are not specified in posix.1, but are present on many other systems. .\" the bsds, hp-ux, solaris, aix, irix. .\" the header location is inconsistent: .\" could be sys/mkdev.h, sys/sysmacros.h, or sys/types.h. .sh notes these interfaces are defined as macros. since glibc 2.3.3, they have been aliases for three gnu-specific functions: .br gnu_dev_makedev (), .br gnu_dev_major (), and .br gnu_dev_minor (). the latter names are exported, but the traditional names are more portable. .pp the bsds expose the definitions for these macros via .ir . depending on the version, glibc also exposes definitions for these macros from that header file if suitable feature test macros are defined. however, this behavior was deprecated in glibc 2.25, .\" glibc commit dbab6577c6684c62bd2521c1c29dc25c3cac966f and since glibc 2.28, .\" glibc commit e16deca62e16f645213dffd4ecd1153c37765f17 .ir no longer provides these definitions. .sh see also .br mknod (2), .br stat (2) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2003 free software foundation, inc. .\" .\" %%%license_start(gpl_noversion_oneline) .\" this file is distributed according to the gnu general public license. .\" %%%license_end .\" .th io_cancel 2 2021-03-22 "linux" "linux programmer's manual" .sh name io_cancel \- cancel an outstanding asynchronous i/o operation .sh synopsis .nf .br "#include " " /* definition of needed types */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "int syscall(sys_io_cancel, aio_context_t " ctx_id ", struct iocb *" iocb , .bi " struct io_event *" result ); .fi .sh description .ir note : this page describes the raw linux system call interface. the wrapper function provided by .i libaio uses a different type for the .i ctx_id argument. see notes. .pp the .br io_cancel () system call attempts to cancel an asynchronous i/o operation previously submitted with .br io_submit (2). the .i iocb argument describes the operation to be canceled and the .i ctx_id argument is the aio context to which the operation was submitted. if the operation is successfully canceled, the event will be copied into the memory pointed to by .i result without being placed into the completion queue. .sh return value on success, .br io_cancel () returns 0. for the failure return, see notes. .sh errors .tp .b eagain the \fiiocb\fp specified was not canceled. .tp .b efault one of the data structures points to invalid data. .tp .b einval the aio context specified by \fictx_id\fp is invalid. .tp .b enosys .br io_cancel () is not implemented on this architecture. .sh versions the asynchronous i/o system calls first appeared in linux 2.5. .sh conforming to .br io_cancel () is linux-specific and should not be used in programs that are intended to be portable. .sh notes you probably want to use the .br io_cancel () wrapper function provided by .\" http://git.fedorahosted.org/git/?p=libaio.git .ir libaio . .pp note that the .i libaio wrapper function uses a different type .ri ( io_context_t ) .\" but glibc is confused, since uses 'io_context_t' to declare .\" the system call. for the .i ctx_id argument. note also that the .i libaio wrapper does not follow the usual c library conventions for indicating errors: on error it returns a negated error number (the negative of one of the values listed in errors). if the system call is invoked via .br syscall (2), then the return value follows the usual conventions for indicating an error: \-1, with .i errno set to a (positive) value that indicates the error. .sh see also .br io_destroy (2), .br io_getevents (2), .br io_setup (2), .br io_submit (2), .br aio (7) .\" .sh author .\" kent yoder. .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/drand48_r.3 .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th iswpunct 3 2021-03-22 "gnu" "linux programmer's manual" .sh name iswpunct \- test for punctuation or symbolic wide character .sh synopsis .nf .b #include .pp .bi "int iswpunct(wint_t " wc ); .fi .sh description the .br iswpunct () function is the wide-character equivalent of the .br ispunct (3) function. it tests whether .i wc is a wide character belonging to the wide-character class "punct". .pp the wide-character class "punct" is a subclass of the wide-character class "graph", and therefore also a subclass of the wide-character class "print". .pp the wide-character class "punct" is disjoint from the wide-character class "alnum" and therefore also disjoint from its subclasses "alpha", "upper", "lower", "digit", "xdigit". .pp being a subclass of the wide-character class "print", the wide-character class "punct" is disjoint from the wide-character class "cntrl". .pp being a subclass of the wide-character class "graph", the wide-character class "punct" is disjoint from the wide-character class "space" and its subclass "blank". .sh return value the .br iswpunct () function returns nonzero if .i wc is a wide-character belonging to the wide-character class "punct". otherwise, it returns zero. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br iswpunct () t} thread safety mt-safe locale .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh notes the behavior of .br iswpunct () depends on the .b lc_ctype category of the current locale. .pp this function's name is a misnomer when dealing with unicode characters, because the wide-character class "punct" contains both punctuation characters and symbol (math, currency, etc.) characters. .sh see also .br ispunct (3), .br iswctype (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2003 andi kleen .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th arch_prctl 2 2021-08-27 "linux" "linux programmer's manual" .sh name arch_prctl \- set architecture-specific thread state .sh synopsis .nf .br "#include " " /* definition of " arch_* " constants */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "int syscall(sys_arch_prctl, int " code ", unsigned long " addr ); .bi "int syscall(sys_arch_prctl, int " code ", unsigned long *" addr ); .fi .pp .ir note : glibc provides no wrapper for .br arch_prctl (), necessitating the use of .br syscall (2). .sh description .br arch_prctl () sets architecture-specific process or thread state. .i code selects a subfunction and passes argument .i addr to it; .i addr is interpreted as either an .i "unsigned long" for the "set" operations, or as an .ir "unsigned long\ *" , for the "get" operations. .pp subfunctions for both x86 and x86-64 are: .tp .br arch_set_cpuid " (since linux 4.12)" .\" commit e9ea1e7f53b852147cbd568b0568c7ad97ec21a3 enable .ri ( "addr != 0" ) or disable .ri ( "addr == 0" ) the .i cpuid instruction for the calling thread. the instruction is enabled by default. if disabled, any execution of a .i cpuid instruction will instead generate a .b sigsegv signal. this feature can be used to emulate .i cpuid results that differ from what the underlying hardware would have produced (e.g., in a paravirtualization setting). .ip the .br arch_set_cpuid setting is preserved across .br fork (2) and .br clone (2) but reset to the default (i.e., .i cpuid enabled) on .br execve (2). .tp .br arch_get_cpuid " (since linux 4.12)" return the setting of the flag manipulated by .b arch_set_cpuid as the result of the system call (1 for enabled, 0 for disabled). .i addr is ignored. .tp subfunctions for x86-64 only are: .tp .b arch_set_fs set the 64-bit base for the .i fs register to .ir addr . .tp .b arch_get_fs return the 64-bit base value for the .i fs register of the calling thread in the .i unsigned long pointed to by .ir addr . .tp .b arch_set_gs set the 64-bit base for the .i gs register to .ir addr . .tp .b arch_get_gs return the 64-bit base value for the .i gs register of the calling thread in the .i unsigned long pointed to by .ir addr . .sh return value on success, .br arch_prctl () returns 0; on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b efault .i addr points to an unmapped address or is outside the process address space. .tp .b einval .i code is not a valid subcommand. .tp .b enodev .b arch_set_cpuid was requested, but the underlying hardware does not support cpuid faulting. .tp .b eperm .i addr is outside the process address space. .\" .sh author .\" man page written by andi kleen. .sh conforming to .br arch_prctl () is a linux/x86-64 extension and should not be used in programs intended to be portable. .sh notes .br arch_prctl () is supported only on linux/x86-64 for 64-bit programs currently. .pp the 64-bit base changes when a new 32-bit segment selector is loaded. .pp .b arch_set_gs is disabled in some kernels. .pp context switches for 64-bit segment bases are rather expensive. as an optimization, if a 32-bit tls base address is used, .br arch_prctl () may use a real tls entry as if .br set_thread_area (2) had been called, instead of manipulating the segment base register directly. memory in the first 2\ gb of address space can be allocated by using .br mmap (2) with the .b map_32bit flag. .pp because of the aforementioned optimization, using .br arch_prctl () and .br set_thread_area (2) in the same thread is dangerous, as they may overwrite each other's tls entries. .pp .i fs may be already used by the threading library. programs that use .b arch_set_fs directly are very likely to crash. .sh see also .br mmap (2), .br modify_ldt (2), .br prctl (2), .br set_thread_area (2) .pp amd x86-64 programmer's manual .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/utimensat.2 .so man7/system_data_types.7 .\" copyright (c) 2000 andries brouwer .\" and copyright (c) 2007 michael kerrisk .\" and copyright (c) 2008, linux foundation, written by michael kerrisk .\" .\" based on work by rik faith .\" and mike battersby . .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified 2004-11-19, mtk: .\" added pointer to sigaction.2 for details of ignoring sigchld .\" 2007-06-03, mtk: strengthened portability warning, and rewrote .\" various sections. .\" 2008-07-11, mtk: rewrote and expanded portability discussion. .\" .th signal 2 2021-03-22 "linux" "linux programmer's manual" .sh name signal \- ansi c signal handling .sh synopsis .nf .b #include .pp .b typedef void (*sighandler_t)(int); .pp .bi "sighandler_t signal(int " signum ", sighandler_t " handler ); .fi .sh description .br warning : the behavior of .br signal () varies across unix versions, and has also varied historically across different versions of linux. \fbavoid its use\fp: use .br sigaction (2) instead. see \fiportability\fp below. .pp .br signal () sets the disposition of the signal .i signum to .ir handler , which is either .br sig_ign , .br sig_dfl , or the address of a programmer-defined function (a "signal handler"). .pp if the signal .i signum is delivered to the process, then one of the following happens: .tp 3 * if the disposition is set to .br sig_ign , then the signal is ignored. .tp * if the disposition is set to .br sig_dfl , then the default action associated with the signal (see .br signal (7)) occurs. .tp * if the disposition is set to a function, then first either the disposition is reset to .br sig_dfl , or the signal is blocked (see \fiportability\fp below), and then .i handler is called with argument .ir signum . if invocation of the handler caused the signal to be blocked, then the signal is unblocked upon return from the handler. .pp the signals .b sigkill and .b sigstop cannot be caught or ignored. .sh return value .br signal () returns the previous value of the signal handler on failure, it returns .br sig_err , and .i errno is set to indicate the error. .sh errors .tp .b einval .i signum is invalid. .sh conforming to posix.1-2001, posix.1-2008, c89, c99. .sh notes the effects of .br signal () in a multithreaded process are unspecified. .pp according to posix, the behavior of a process is undefined after it ignores a .br sigfpe , .br sigill , or .b sigsegv signal that was not generated by .br kill (2) or .br raise (3). integer division by zero has undefined result. on some architectures it will generate a .b sigfpe signal. (also dividing the most negative integer by \-1 may generate .br sigfpe .) ignoring this signal might lead to an endless loop. .pp see .br sigaction (2) for details on what happens when the disposition .b sigchld is set to .br sig_ign . .pp see .br signal\-safety (7) for a list of the async-signal-safe functions that can be safely called from inside a signal handler. .pp the use of .i sighandler_t is a gnu extension, exposed if .b _gnu_source is defined; .\" libc4 and libc5 define .\" .ir signalhandler ; glibc also defines (the bsd-derived) .i sig_t if .b _bsd_source (glibc 2.19 and earlier) or .br _default_source (glibc 2.19 and later) is defined. without use of such a type, the declaration of .br signal () is the somewhat harder to read: .pp .in +4n .ex .bi "void ( *" signal "(int " signum ", void (*" handler ")(int)) ) (int);" .ee .in .ss portability the only portable use of .br signal () is to set a signal's disposition to .br sig_dfl or .br sig_ign . the semantics when using .br signal () to establish a signal handler vary across systems (and posix.1 explicitly permits this variation); .b do not use it for this purpose. .pp posix.1 solved the portability mess by specifying .br sigaction (2), which provides explicit control of the semantics when a signal handler is invoked; use that interface instead of .br signal (). .pp in the original unix systems, when a handler that was established using .br signal () was invoked by the delivery of a signal, the disposition of the signal would be reset to .br sig_dfl , and the system did not block delivery of further instances of the signal. this is equivalent to calling .br sigaction (2) with the following flags: .pp .in +4n .ex sa.sa_flags = sa_resethand | sa_nodefer; .ee .in .pp system\ v also provides these semantics for .br signal (). this was bad because the signal might be delivered again before the handler had a chance to reestablish itself. furthermore, rapid deliveries of the same signal could result in recursive invocations of the handler. .pp bsd improved on this situation, but unfortunately also changed the semantics of the existing .br signal () interface while doing so. on bsd, when a signal handler is invoked, the signal disposition is not reset, and further instances of the signal are blocked from being delivered while the handler is executing. furthermore, certain blocking system calls are automatically restarted if interrupted by a signal handler (see .br signal (7)). the bsd semantics are equivalent to calling .br sigaction (2) with the following flags: .pp .in +4n .ex sa.sa_flags = sa_restart; .ee .in .pp the situation on linux is as follows: .ip * 2 the kernel's .br signal () system call provides system\ v semantics. .ip * by default, in glibc 2 and later, the .br signal () wrapper function does not invoke the kernel system call. instead, it calls .br sigaction (2) using flags that supply bsd semantics. this default behavior is provided as long as a suitable feature test macro is defined: .b _bsd_source on glibc 2.19 and earlier or .br _default_source in glibc 2.19 and later. (by default, these macros are defined; see .br feature_test_macros (7) for details.) if such a feature test macro is not defined, then .br signal () provides system\ v semantics. .\" .\" system v semantics are also provided if one uses the separate .\" .br sysv_signal (3) .\" function. .\" .ip * .\" the .\" .br signal () .\" function in linux libc4 and libc5 provide system\ v semantics. .\" if one on a libc5 system includes .\" .i .\" instead of .\" .ir , .\" then .\" .br signal () .\" provides bsd semantics. .sh see also .br kill (1), .br alarm (2), .br kill (2), .br pause (2), .br sigaction (2), .br signalfd (2), .br sigpending (2), .br sigprocmask (2), .br sigsuspend (2), .br bsd_signal (3), .br killpg (3), .br raise (3), .br siginterrupt (3), .br sigqueue (3), .br sigsetops (3), .br sigvec (3), .br sysv_signal (3), .br signal (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2013, 2014 by michael kerrisk .\" and copyright (c) 2012, 2014 by eric w. biederman .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" .th user_namespaces 7 2021-08-27 "linux" "linux programmer's manual" .sh name user_namespaces \- overview of linux user namespaces .sh description for an overview of namespaces, see .br namespaces (7). .pp user namespaces isolate security-related identifiers and attributes, in particular, user ids and group ids (see .br credentials (7)), the root directory, keys (see .br keyrings (7)), .\" fixme: this page says very little about the interaction .\" of user namespaces and keys. add something on this topic. and capabilities (see .br capabilities (7)). a process's user and group ids can be different inside and outside a user namespace. in particular, a process can have a normal unprivileged user id outside a user namespace while at the same time having a user id of 0 inside the namespace; in other words, the process has full privileges for operations inside the user namespace, but is unprivileged for operations outside the namespace. .\" .\" ============================================================ .\" .ss nested namespaces, namespace membership user namespaces can be nested; that is, each user namespace\(emexcept the initial ("root") namespace\(emhas a parent user namespace, and can have zero or more child user namespaces. the parent user namespace is the user namespace of the process that creates the user namespace via a call to .br unshare (2) or .br clone (2) with the .br clone_newuser flag. .pp the kernel imposes (since version 3.11) a limit of 32 nested levels of .\" commit 8742f229b635bf1c1c84a3dfe5e47c814c20b5c8 user namespaces. .\" fixme explain the rationale for this limit. (what is the rationale?) calls to .br unshare (2) or .br clone (2) that would cause this limit to be exceeded fail with the error .br eusers . .pp each process is a member of exactly one user namespace. a process created via .br fork (2) or .br clone (2) without the .br clone_newuser flag is a member of the same user namespace as its parent. a single-threaded process can join another user namespace with .br setns (2) if it has the .br cap_sys_admin in that namespace; upon doing so, it gains a full set of capabilities in that namespace. .pp a call to .br clone (2) or .br unshare (2) with the .br clone_newuser flag makes the new child process (for .br clone (2)) or the caller (for .br unshare (2)) a member of the new user namespace created by the call. .pp the .br ns_get_parent .br ioctl (2) operation can be used to discover the parental relationship between user namespaces; see .br ioctl_ns (2). .\" .\" ============================================================ .\" .ss capabilities the child process created by .br clone (2) with the .br clone_newuser flag starts out with a complete set of capabilities in the new user namespace. likewise, a process that creates a new user namespace using .br unshare (2) or joins an existing user namespace using .br setns (2) gains a full set of capabilities in that namespace. on the other hand, that process has no capabilities in the parent (in the case of .br clone (2)) or previous (in the case of .br unshare (2) and .br setns (2)) user namespace, even if the new namespace is created or joined by the root user (i.e., a process with user id 0 in the root namespace). .pp note that a call to .br execve (2) will cause a process's capabilities to be recalculated in the usual way (see .br capabilities (7)). consequently, unless the process has a user id of 0 within the namespace, or the executable file has a nonempty inheritable capabilities mask, the process will lose all capabilities. see the discussion of user and group id mappings, below. .pp a call to .br clone (2) or .br unshare (2) using the .br clone_newuser flag or a call to .br setns (2) that moves the caller into another user namespace sets the "securebits" flags (see .br capabilities (7)) to their default values (all flags disabled) in the child (for .br clone (2)) or caller (for .br unshare (2) or .br setns (2)). note that because the caller no longer has capabilities in its original user namespace after a call to .br setns (2), it is not possible for a process to reset its "securebits" flags while retaining its user namespace membership by using a pair of .br setns (2) calls to move to another user namespace and then return to its original user namespace. .pp the rules for determining whether or not a process has a capability in a particular user namespace are as follows: .ip 1. 3 a process has a capability inside a user namespace if it is a member of that namespace and it has the capability in its effective capability set. a process can gain capabilities in its effective capability set in various ways. for example, it may execute a set-user-id program or an executable with associated file capabilities. in addition, a process may gain capabilities via the effect of .br clone (2), .br unshare (2), or .br setns (2), as already described. .\" in the 3.8 sources, see security/commoncap.c::cap_capable(): .ip 2. if a process has a capability in a user namespace, then it has that capability in all child (and further removed descendant) namespaces as well. .ip 3. .\" * the owner of the user namespace in the parent of the .\" * user namespace has all caps. when a user namespace is created, the kernel records the effective user id of the creating process as being the "owner" of the namespace. .\" (and likewise associates the effective group id of the creating process .\" with the namespace). a process that resides in the parent of the user namespace .\" see kernel commit 520d9eabce18edfef76a60b7b839d54facafe1f9 for a fix .\" on this point and whose effective user id matches the owner of the namespace has all capabilities in the namespace. .\" this includes the case where the process executes a set-user-id .\" program that confers the effective uid of the creator of the namespace. by virtue of the previous rule, this means that the process has all capabilities in all further removed descendant user namespaces as well. the .b ns_get_owner_uid .br ioctl (2) operation can be used to discover the user id of the owner of the namespace; see .br ioctl_ns (2). .\" .\" ============================================================ .\" .ss effect of capabilities within a user namespace having a capability inside a user namespace permits a process to perform operations (that require privilege) only on resources governed by that namespace. in other words, having a capability in a user namespace permits a process to perform privileged operations on resources that are governed by (nonuser) namespaces owned by (associated with) the user namespace (see the next subsection). .pp on the other hand, there are many privileged operations that affect resources that are not associated with any namespace type, for example, changing the system (i.e., calendar) time (governed by .br cap_sys_time ), loading a kernel module (governed by .br cap_sys_module ), and creating a device (governed by .br cap_mknod ). only a process with privileges in the .i initial user namespace can perform such operations. .pp holding .b cap_sys_admin within the user namespace that owns a process's mount namespace allows that process to create bind mounts and mount the following types of filesystems: .\" fs_flags = fs_userns_mount in kernel sources .pp .rs 4 .pd 0 .ip * 2 .ir /proc (since linux 3.8) .ip * .ir /sys (since linux 3.8) .ip * .ir devpts (since linux 3.9) .ip * .br tmpfs (5) (since linux 3.9) .ip * .ir ramfs (since linux 3.9) .ip * .ir mqueue (since linux 3.9) .ip * .ir bpf .\" commit b2197755b2633e164a439682fb05a9b5ea48f706 (since linux 4.4) .ip * .ir overlayfs .\" commit 92dbc9dedccb9759c7f9f2f0ae6242396376988f .\" commit 4cb2c00c43b3fe88b32f29df4f76da1b92c33224 (since linux 5.11) .pd .re .pp holding .b cap_sys_admin within the user namespace that owns a process's cgroup namespace allows (since linux 4.6) that process to the mount the cgroup version 2 filesystem and cgroup version 1 named hierarchies (i.e., cgroup filesystems mounted with the .ir """none,name=""" option). .pp holding .b cap_sys_admin within the user namespace that owns a process's pid namespace allows (since linux 3.8) that process to mount .i /proc filesystems. .pp note, however, that mounting block-based filesystems can be done only by a process that holds .br cap_sys_admin in the initial user namespace. .\" .\" ============================================================ .\" .ss interaction of user namespaces and other types of namespaces starting in linux 3.8, unprivileged processes can create user namespaces, and the other types of namespaces can be created with just the .b cap_sys_admin capability in the caller's user namespace. .pp when a nonuser namespace is created, it is owned by the user namespace in which the creating process was a member at the time of the creation of the namespace. privileged operations on resources governed by the nonuser namespace require that the process has the necessary capabilities in the user namespace that owns the nonuser namespace. .pp if .br clone_newuser is specified along with other .b clone_new* flags in a single .br clone (2) or .br unshare (2) call, the user namespace is guaranteed to be created first, giving the child .rb ( clone (2)) or caller .rb ( unshare (2)) privileges over the remaining namespaces created by the call. thus, it is possible for an unprivileged caller to specify this combination of flags. .pp when a new namespace (other than a user namespace) is created via .br clone (2) or .br unshare (2), the kernel records the user namespace of the creating process as the owner of the new namespace. (this association can't be changed.) when a process in the new namespace subsequently performs privileged operations that operate on global resources isolated by the namespace, the permission checks are performed according to the process's capabilities in the user namespace that the kernel associated with the new namespace. for example, suppose that a process attempts to change the hostname .rb ( sethostname (2)), a resource governed by the uts namespace. in this case, the kernel will determine which user namespace owns the process's uts namespace, and check whether the process has the required capability .rb ( cap_sys_admin ) in that user namespace. .pp the .br ns_get_userns .br ioctl (2) operation can be used to discover the user namespace that owns a nonuser namespace; see .br ioctl_ns (2). .\" .\" ============================================================ .\" .ss user and group id mappings: uid_map and gid_map when a user namespace is created, it starts out without a mapping of user ids (group ids) to the parent user namespace. the .ir /proc/[pid]/uid_map and .ir /proc/[pid]/gid_map files (available since linux 3.5) .\" commit 22d917d80e842829d0ca0a561967d728eb1d6303 expose the mappings for user and group ids inside the user namespace for the process .ir pid . these files can be read to view the mappings in a user namespace and written to (once) to define the mappings. .pp the description in the following paragraphs explains the details for .ir uid_map ; .ir gid_map is exactly the same, but each instance of "user id" is replaced by "group id". .pp the .i uid_map file exposes the mapping of user ids from the user namespace of the process .ir pid to the user namespace of the process that opened .ir uid_map (but see a qualification to this point below). in other words, processes that are in different user namespaces will potentially see different values when reading from a particular .i uid_map file, depending on the user id mappings for the user namespaces of the reading processes. .pp each line in the .i uid_map file specifies a 1-to-1 mapping of a range of contiguous user ids between two user namespaces. (when a user namespace is first created, this file is empty.) the specification in each line takes the form of three numbers delimited by white space. the first two numbers specify the starting user id in each of the two user namespaces. the third number specifies the length of the mapped range. in detail, the fields are interpreted as follows: .ip (1) 4 the start of the range of user ids in the user namespace of the process .ir pid . .ip (2) the start of the range of user ids to which the user ids specified by field one map. how field two is interpreted depends on whether the process that opened .i uid_map and the process .ir pid are in the same user namespace, as follows: .rs .ip a) 3 if the two processes are in different user namespaces: field two is the start of a range of user ids in the user namespace of the process that opened .ir uid_map . .ip b) if the two processes are in the same user namespace: field two is the start of the range of user ids in the parent user namespace of the process .ir pid . this case enables the opener of .i uid_map (the common case here is opening .ir /proc/self/uid_map ) to see the mapping of user ids into the user namespace of the process that created this user namespace. .re .ip (3) the length of the range of user ids that is mapped between the two user namespaces. .pp system calls that return user ids (group ids)\(emfor example, .br getuid (2), .br getgid (2), and the credential fields in the structure returned by .br stat (2)\(emreturn the user id (group id) mapped into the caller's user namespace. .pp when a process accesses a file, its user and group ids are mapped into the initial user namespace for the purpose of permission checking and assigning ids when creating a file. when a process retrieves file user and group ids via .br stat (2), the ids are mapped in the opposite direction, to produce values relative to the process user and group id mappings. .pp the initial user namespace has no parent namespace, but, for consistency, the kernel provides dummy user and group id mapping files for this namespace. looking at the .i uid_map file .ri ( gid_map is the same) from a shell in the initial namespace shows: .pp .in +4n .ex $ \fbcat /proc/$$/uid_map\fp 0 0 4294967295 .ee .in .pp this mapping tells us that the range starting at user id 0 in this namespace maps to a range starting at 0 in the (nonexistent) parent namespace, and the length of the range is the largest 32-bit unsigned integer. this leaves 4294967295 (the 32-bit signed \-1 value) unmapped. this is deliberate: .ir "(uid_t)\ \-1" is used in several interfaces (e.g., .br setreuid (2)) as a way to specify "no user id". leaving .ir "(uid_t)\ \-1" unmapped and unusable guarantees that there will be no confusion when using these interfaces. .\" .\" ============================================================ .\" .ss defining user and group id mappings: writing to uid_map and gid_map after the creation of a new user namespace, the .i uid_map file of .i one of the processes in the namespace may be written to .i once to define the mapping of user ids in the new user namespace. an attempt to write more than once to a .i uid_map file in a user namespace fails with the error .br eperm . similar rules apply for .i gid_map files. .pp the lines written to .ir uid_map .ri ( gid_map ) must conform to the following validity rules: .ip * 3 the three fields must be valid numbers, and the last field must be greater than 0. .ip * lines are terminated by newline characters. .ip * there is a limit on the number of lines in the file. in linux 4.14 and earlier, this limit was (arbitrarily) .\" 5*12-byte records could fit in a 64b cache line set at 5 lines. since linux 4.15, .\" commit 6397fac4915ab3002dc15aae751455da1a852f25 the limit is 340 lines. in addition, the number of bytes written to the file must be less than the system page size, and the write must be performed at the start of the file (i.e., .br lseek (2) and .br pwrite (2) can't be used to write to nonzero offsets in the file). .ip * the range of user ids (group ids) specified in each line cannot overlap with the ranges in any other lines. in the initial implementation (linux 3.8), this requirement was satisfied by a simplistic implementation that imposed the further requirement that the values in both field 1 and field 2 of successive lines must be in ascending numerical order, which prevented some otherwise valid maps from being created. linux 3.9 and later .\" commit 0bd14b4fd72afd5df41e9fd59f356740f22fceba fix this limitation, allowing any valid set of nonoverlapping maps. .ip * at least one line must be written to the file. .pp writes that violate the above rules fail with the error .br einval . .pp in order for a process to write to the .i /proc/[pid]/uid_map .ri ( /proc/[pid]/gid_map ) file, all of the following permission requirements must be met: .ip 1. 3 the writing process must have the .br cap_setuid .rb ( cap_setgid ) capability in the user namespace of the process .ir pid . .ip 2. the writing process must either be in the user namespace of the process .i pid or be in the parent user namespace of the process .ir pid . .ip 3. the mapped user ids (group ids) must in turn have a mapping in the parent user namespace. .ip 4. if updating .ir /proc/[pid]/uid_map to create a mapping that maps uid 0 in the parent namespace, then one of the following must be true: .rs .ip * 3 if writing process is in the parent user namespace, then it must have the .br cap_setfcap capability in that user namespace; or .ip * if the writing process is in the child user namespace, then the process that created the user namespace must have had the .br cap_setfcap capability when the namespace was created. .re .ip this rule has been in place since .\" commit db2e718a47984b9d71ed890eb2ea36ecf150de18 linux 5.12. it eliminates an earlier security bug whereby a uid 0 process that lacks the .b cap_setfcap capability, which is needed to create a binary with namespaced file capabilities (as described in .br capabilities (7)), could nevertheless create such a binary, by the following steps: .rs .ip * 3 create a new user namespace with the identity mapping (i.e., uid 0 in the new user namespace maps to uid 0 in the parent namespace), so that uid 0 in both namespaces is equivalent to the same root user id. .ip * since the child process has the .b cap_setfcap capability, it could create a binary with namespaced file capabilities that would then be effective in the parent user namespace (because the root user ids are the same in the two namespaces). .re .ip 5. one of the following two cases applies: .rs .ip * 3 .ir either the writing process has the .br cap_setuid .rb ( cap_setgid ) capability in the .i parent user namespace. .rs .ip + 3 no further restrictions apply: the process can make mappings to arbitrary user ids (group ids) in the parent user namespace. .re .ip * 3 .ir or otherwise all of the following restrictions apply: .rs .ip + 3 the data written to .i uid_map .ri ( gid_map ) must consist of a single line that maps the writing process's effective user id (group id) in the parent user namespace to a user id (group id) in the user namespace. .ip + the writing process must have the same effective user id as the process that created the user namespace. .ip + in the case of .ir gid_map , use of the .br setgroups (2) system call must first be denied by writing .ri \(dq deny \(dq to the .i /proc/[pid]/setgroups file (see below) before writing to .ir gid_map . .re .re .pp writes that violate the above rules fail with the error .br eperm . .\" .\" ============================================================ .\" .ss project id mappings: projid_map similarly to user and group id mappings, it is possible to create project id mappings for a user namespace. (project ids are used for disk quotas; see .br setquota (8) and .br quotactl (2).) .pp project id mappings are defined by writing to the .i /proc/[pid]/projid_map file (present since .\" commit f76d207a66c3a53defea67e7d36c3eb1b7d6d61d linux 3.7). .pp the validity rules for writing to the .i /proc/[pid]/projid_map file are as for writing to the .i uid_map file; violation of these rules causes .br write (2) to fail with the error .br einval . .pp the permission rules for writing to the .i /proc/[pid]/projid_map file are as follows: .ip 1. 3 the writing process must either be in the user namespace of the process .i pid or be in the parent user namespace of the process .ir pid . .ip 2. the mapped project ids must in turn have a mapping in the parent user namespace. .pp violation of these rules causes .br write (2) to fail with the error .br eperm . .\" .\" ============================================================ .\" .ss interaction with system calls that change process uids or gids in a user namespace where the .i uid_map file has not been written, the system calls that change user ids will fail. similarly, if the .i gid_map file has not been written, the system calls that change group ids will fail. after the .i uid_map and .i gid_map files have been written, only the mapped values may be used in system calls that change user and group ids. .pp for user ids, the relevant system calls include .br setuid (2), .br setfsuid (2), .br setreuid (2), and .br setresuid (2). for group ids, the relevant system calls include .br setgid (2), .br setfsgid (2), .br setregid (2), .br setresgid (2), and .br setgroups (2). .pp writing .ri \(dq deny \(dq to the .i /proc/[pid]/setgroups file before writing to .i /proc/[pid]/gid_map .\" things changed in linux 3.19 .\" commit 9cc46516ddf497ea16e8d7cb986ae03a0f6b92f8 .\" commit 66d2f338ee4c449396b6f99f5e75cd18eb6df272 .\" http://lwn.net/articles/626665/ will permanently disable .br setgroups (2) in a user namespace and allow writing to .i /proc/[pid]/gid_map without having the .br cap_setgid capability in the parent user namespace. .\" .\" ============================================================ .\" .ss the /proc/[pid]/setgroups file .\" .\" commit 9cc46516ddf497ea16e8d7cb986ae03a0f6b92f8 .\" commit 66d2f338ee4c449396b6f99f5e75cd18eb6df272 .\" http://lwn.net/articles/626665/ .\" http://web.nvd.nist.gov/view/vuln/detail?vulnid=cve-2014-8989 .\" the .i /proc/[pid]/setgroups file displays the string .ri \(dq allow \(dq if processes in the user namespace that contains the process .i pid are permitted to employ the .br setgroups (2) system call; it displays .ri \(dq deny \(dq if .br setgroups (2) is not permitted in that user namespace. note that regardless of the value in the .i /proc/[pid]/setgroups file (and regardless of the process's capabilities), calls to .br setgroups (2) are also not permitted if .ir /proc/[pid]/gid_map has not yet been set. .pp a privileged process (one with the .br cap_sys_admin capability in the namespace) may write either of the strings .ri \(dq allow \(dq or .ri \(dq deny \(dq to this file .i before writing a group id mapping for this user namespace to the file .ir /proc/[pid]/gid_map . writing the string .ri \(dq deny \(dq prevents any process in the user namespace from employing .br setgroups (2). .pp the essence of the restrictions described in the preceding paragraph is that it is permitted to write to .i /proc/[pid]/setgroups only so long as calling .br setgroups (2) is disallowed because .i /proc/[pid]/gid_map has not been set. this ensures that a process cannot transition from a state where .br setgroups (2) is allowed to a state where .br setgroups (2) is denied; a process can transition only from .br setgroups (2) being disallowed to .br setgroups (2) being allowed. .pp the default value of this file in the initial user namespace is .ri \(dq allow \(dq. .pp once .ir /proc/[pid]/gid_map has been written to (which has the effect of enabling .br setgroups (2) in the user namespace), it is no longer possible to disallow .br setgroups (2) by writing .ri \(dq deny \(dq to .ir /proc/[pid]/setgroups (the write fails with the error .br eperm ). .pp a child user namespace inherits the .ir /proc/[pid]/setgroups setting from its parent. .pp if the .i setgroups file has the value .ri \(dq deny \(dq, then the .br setgroups (2) system call can't subsequently be reenabled (by writing .ri \(dq allow \(dq to the file) in this user namespace. (attempts to do so fail with the error .br eperm .) this restriction also propagates down to all child user namespaces of this user namespace. .pp the .i /proc/[pid]/setgroups file was added in linux 3.19, but was backported to many earlier stable kernel series, because it addresses a security issue. the issue concerned files with permissions such as "rwx\-\-\-rwx". such files give fewer permissions to "group" than they do to "other". this means that dropping groups using .br setgroups (2) might allow a process file access that it did not formerly have. before the existence of user namespaces this was not a concern, since only a privileged process (one with the .br cap_setgid capability) could call .br setgroups (2). however, with the introduction of user namespaces, it became possible for an unprivileged process to create a new namespace in which the user had all privileges. this then allowed formerly unprivileged users to drop groups and thus gain file access that they did not previously have. the .i /proc/[pid]/setgroups file was added to address this security issue, by denying any pathway for an unprivileged process to drop groups with .br setgroups (2). .\" .\" /proc/pid/setgroups .\" [allow == setgroups() is allowed, "deny" == setgroups() is disallowed] .\" * can write if have cap_sys_admin in ns .\" * must write before writing to /proc/pid/gid_map .\" .\" setgroups() .\" * must already have written to gid_map .\" * /proc/pid/setgroups must be "allow" .\" .\" /proc/pid/gid_map -- writing .\" * must already have written "deny" to /proc/pid/setgroups .\" .\" ============================================================ .\" .ss unmapped user and group ids there are various places where an unmapped user id (group id) may be exposed to user space. for example, the first process in a new user namespace may call .br getuid (2) before a user id mapping has been defined for the namespace. in most such cases, an unmapped user id is converted .\" from_kuid_munged(), from_kgid_munged() to the overflow user id (group id); the default value for the overflow user id (group id) is 65534. see the descriptions of .ir /proc/sys/kernel/overflowuid and .ir /proc/sys/kernel/overflowgid in .br proc (5). .pp the cases where unmapped ids are mapped in this fashion include system calls that return user ids .rb ( getuid (2), .br getgid (2), and similar), credentials passed over a unix domain socket, .\" also so_peercred credentials returned by .br stat (2), .br waitid (2), and the system v ipc "ctl" .b ipc_stat operations, credentials exposed by .ir /proc/[pid]/status and the files in .ir /proc/sysvipc/* , credentials returned via the .i si_uid field in the .i siginfo_t received with a signal (see .br sigaction (2)), credentials written to the process accounting file (see .br acct (5)), and credentials returned with posix message queue notifications (see .br mq_notify (3)). .pp there is one notable case where unmapped user and group ids are .i not .\" from_kuid(), from_kgid() .\" also f_getowner_uids is an exception converted to the corresponding overflow id value. when viewing a .i uid_map or .i gid_map file in which there is no mapping for the second field, that field is displayed as 4294967295 (\-1 as an unsigned integer). .\" .\" ============================================================ .\" .ss accessing files in order to determine permissions when an unprivileged process accesses a file, the process credentials (uid, gid) and the file credentials are in effect mapped back to what they would be in the initial user namespace and then compared to determine the permissions that the process has on the file. the same is also of other objects that employ the credentials plus permissions mask accessibility model, such as system v ipc objects .\" .\" ============================================================ .\" .ss operation of file-related capabilities certain capabilities allow a process to bypass various kernel-enforced restrictions when performing operations on files owned by other users or groups. these capabilities are: .br cap_chown , .br cap_dac_override , .br cap_dac_read_search , .br cap_fowner , and .br cap_fsetid . .pp within a user namespace, these capabilities allow a process to bypass the rules if the process has the relevant capability over the file, meaning that: .ip * 3 the process has the relevant effective capability in its user namespace; and .ip * the file's user id and group id both have valid mappings in the user namespace. .pp the .br cap_fowner capability is treated somewhat exceptionally: .\" these are the checks performed by the kernel function .\" inode_owner_or_capable(). there is one exception to the exception: .\" overriding the directory sticky permission bit requires that .\" the file has a valid mapping for both its uid and gid. it allows a process to bypass the corresponding rules so long as at least the file's user id has a mapping in the user namespace (i.e., the file's group id does not need to have a valid mapping). .\" .\" ============================================================ .\" .ss set-user-id and set-group-id programs when a process inside a user namespace executes a set-user-id (set-group-id) program, the process's effective user (group) id inside the namespace is changed to whatever value is mapped for the user (group) id of the file. however, if either the user .i or the group id of the file has no mapping inside the namespace, the set-user-id (set-group-id) bit is silently ignored: the new program is executed, but the process's effective user (group) id is left unchanged. (this mirrors the semantics of executing a set-user-id or set-group-id program that resides on a filesystem that was mounted with the .br ms_nosuid flag, as described in .br mount (2).) .\" .\" ============================================================ .\" .ss miscellaneous when a process's user and group ids are passed over a unix domain socket to a process in a different user namespace (see the description of .b scm_credentials in .br unix (7)), they are translated into the corresponding values as per the receiving process's user and group id mappings. .\" .sh conforming to namespaces are a linux-specific feature. .\" .sh notes over the years, there have been a lot of features that have been added to the linux kernel that have been made available only to privileged users because of their potential to confuse set-user-id-root applications. in general, it becomes safe to allow the root user in a user namespace to use those features because it is impossible, while in a user namespace, to gain more privilege than the root user of a user namespace has. .\" .\" ============================================================ .\" .ss global root the term "global root" is sometimes used as a shorthand for user id 0 in the initial user namespace. .\" .\" ============================================================ .\" .ss availability use of user namespaces requires a kernel that is configured with the .b config_user_ns option. user namespaces require support in a range of subsystems across the kernel. when an unsupported subsystem is configured into the kernel, it is not possible to configure user namespaces support. .pp as at linux 3.8, most relevant subsystems supported user namespaces, but a number of filesystems did not have the infrastructure needed to map user and group ids between user namespaces. linux 3.9 added the required infrastructure support for many of the remaining unsupported filesystems (plan 9 (9p), andrew file system (afs), ceph, cifs, coda, nfs, and ocfs2). linux 3.12 added support for the last of the unsupported major filesystems, .\" commit d6970d4b726cea6d7a9bc4120814f95c09571fc3 xfs. .\" .sh examples the program below is designed to allow experimenting with user namespaces, as well as other types of namespaces. it creates namespaces as specified by command-line options and then executes a command inside those namespaces. the comments and .i usage() function inside the program provide a full explanation of the program. the following shell session demonstrates its use. .pp first, we look at the run-time environment: .pp .in +4n .ex $ \fbuname \-rs\fp # need linux 3.8 or later linux 3.8.0 $ \fbid \-u\fp # running as unprivileged user 1000 $ \fbid \-g\fp 1000 .ee .in .pp now start a new shell in new user .ri ( \-u ), mount .ri ( \-m ), and pid .ri ( \-p ) namespaces, with user id .ri ( \-m ) and group id .ri ( \-g ) 1000 mapped to 0 inside the user namespace: .pp .in +4n .ex $ \fb./userns_child_exec \-p \-m \-u \-m \(aq0 1000 1\(aq \-g \(aq0 1000 1\(aq bash\fp .ee .in .pp the shell has pid 1, because it is the first process in the new pid namespace: .pp .in +4n .ex bash$ \fbecho $$\fp 1 .ee .in .pp mounting a new .i /proc filesystem and listing all of the processes visible in the new pid namespace shows that the shell can't see any processes outside the pid namespace: .pp .in +4n .ex bash$ \fbmount \-t proc proc /proc\fp bash$ \fbps ax\fp pid tty stat time command 1 pts/3 s 0:00 bash 22 pts/3 r+ 0:00 ps ax .ee .in .pp inside the user namespace, the shell has user and group id 0, and a full set of permitted and effective capabilities: .pp .in +4n .ex bash$ \fbcat /proc/$$/status | egrep \(aq\(ha[ug]id\(aq\fp uid: 0 0 0 0 gid: 0 0 0 0 bash$ \fbcat /proc/$$/status | egrep \(aq\(hacap(prm|inh|eff)\(aq\fp capinh: 0000000000000000 capprm: 0000001fffffffff capeff: 0000001fffffffff .ee .in .ss program source \& .ex /* userns_child_exec.c licensed under gnu general public license v2 or later create a child process that executes a shell command in new namespace(s); allow uid and gid mappings to be specified when creating a user namespace. */ #define _gnu_source #include #include #include #include #include #include #include #include #include #include #include /* a simple error\-handling function: print an error message based on the value in \(aqerrno\(aq and terminate the calling process. */ #define errexit(msg) do { perror(msg); exit(exit_failure); \e } while (0) struct child_args { char **argv; /* command to be executed by child, with args */ int pipe_fd[2]; /* pipe used to synchronize parent and child */ }; static int verbose; static void usage(char *pname) { fprintf(stderr, "usage: %s [options] cmd [arg...]\en\en", pname); fprintf(stderr, "create a child process that executes a shell " "command in a new user namespace,\en" "and possibly also other new namespace(s).\en\en"); fprintf(stderr, "options can be:\en\en"); #define fpe(str) fprintf(stderr, " %s", str); fpe("\-i new ipc namespace\en"); fpe("\-m new mount namespace\en"); fpe("\-n new network namespace\en"); fpe("\-p new pid namespace\en"); fpe("\-u new uts namespace\en"); fpe("\-u new user namespace\en"); fpe("\-m uid_map specify uid map for user namespace\en"); fpe("\-g gid_map specify gid map for user namespace\en"); fpe("\-z map user\(aqs uid and gid to 0 in user namespace\en"); fpe(" (equivalent to: \-m \(aq0 1\(aq \-g \(aq0 1\(aq)\en"); fpe("\-v display verbose messages\en"); fpe("\en"); fpe("if \-z, \-m, or \-g is specified, \-u is required.\en"); fpe("it is not permitted to specify both \-z and either \-m or \-g.\en"); fpe("\en"); fpe("map strings for \-m and \-g consist of records of the form:\en"); fpe("\en"); fpe(" id\-inside\-ns id\-outside\-ns len\en"); fpe("\en"); fpe("a map string can contain multiple records, separated" " by commas;\en"); fpe("the commas are replaced by newlines before writing" " to map files.\en"); exit(exit_failure); } /* update the mapping file \(aqmap_file\(aq, with the value provided in \(aqmapping\(aq, a string that defines a uid or gid mapping. a uid or gid mapping consists of one or more newline\-delimited records of the form: id_inside\-ns id\-outside\-ns length requiring the user to supply a string that contains newlines is of course inconvenient for command\-line use. thus, we permit the use of commas to delimit records in this string, and replace them with newlines before writing the string to the file. */ static void update_map(char *mapping, char *map_file) { int fd; size_t map_len; /* length of \(aqmapping\(aq */ /* replace commas in mapping string with newlines. */ map_len = strlen(mapping); for (int j = 0; j < map_len; j++) if (mapping[j] == \(aq,\(aq) mapping[j] = \(aq\en\(aq; fd = open(map_file, o_rdwr); if (fd == \-1) { fprintf(stderr, "error: open %s: %s\en", map_file, strerror(errno)); exit(exit_failure); } if (write(fd, mapping, map_len) != map_len) { fprintf(stderr, "error: write %s: %s\en", map_file, strerror(errno)); exit(exit_failure); } close(fd); } /* linux 3.19 made a change in the handling of setgroups(2) and the \(aqgid_map\(aq file to address a security issue. the issue allowed *unprivileged* users to employ user namespaces in order to drop the upshot of the 3.19 changes is that in order to update the \(aqgid_maps\(aq file, use of the setgroups() system call in this user namespace must first be disabled by writing "deny" to one of the /proc/pid/setgroups files for this namespace. that is the purpose of the following function. */ static void proc_setgroups_write(pid_t child_pid, char *str) { char setgroups_path[path_max]; int fd; snprintf(setgroups_path, path_max, "/proc/%jd/setgroups", (intmax_t) child_pid); fd = open(setgroups_path, o_rdwr); if (fd == \-1) { /* we may be on a system that doesn\(aqt support /proc/pid/setgroups. in that case, the file won\(aqt exist, and the system won\(aqt impose the restrictions that linux 3.19 added. that\(aqs fine: we don\(aqt need to do anything in order to permit \(aqgid_map\(aq to be updated. however, if the error from open() was something other than the enoent error that is expected for that case, let the user know. */ if (errno != enoent) fprintf(stderr, "error: open %s: %s\en", setgroups_path, strerror(errno)); return; } if (write(fd, str, strlen(str)) == \-1) fprintf(stderr, "error: write %s: %s\en", setgroups_path, strerror(errno)); close(fd); } static int /* start function for cloned child */ childfunc(void *arg) { struct child_args *args = arg; char ch; /* wait until the parent has updated the uid and gid mappings. see the comment in main(). we wait for end of file on a pipe that will be closed by the parent process once it has updated the mappings. */ close(args\->pipe_fd[1]); /* close our descriptor for the write end of the pipe so that we see eof when parent closes its descriptor. */ if (read(args\->pipe_fd[0], &ch, 1) != 0) { fprintf(stderr, "failure in child: read from pipe returned != 0\en"); exit(exit_failure); } close(args\->pipe_fd[0]); /* execute a shell command. */ printf("about to exec %s\en", args\->argv[0]); execvp(args\->argv[0], args\->argv); errexit("execvp"); } #define stack_size (1024 * 1024) static char child_stack[stack_size]; /* space for child\(aqs stack */ int main(int argc, char *argv[]) { int flags, opt, map_zero; pid_t child_pid; struct child_args args; char *uid_map, *gid_map; const int map_buf_size = 100; char map_buf[map_buf_size]; char map_path[path_max]; /* parse command\-line options. the initial \(aq+\(aq character in the final getopt() argument prevents gnu\-style permutation of command\-line options. that\(aqs useful, since sometimes the \(aqcommand\(aq to be executed by this program itself has command\-line options. we don\(aqt want getopt() to treat those as options to this program. */ flags = 0; verbose = 0; gid_map = null; uid_map = null; map_zero = 0; while ((opt = getopt(argc, argv, "+imnpuum:g:zv")) != \-1) { switch (opt) { case \(aqi\(aq: flags |= clone_newipc; break; case \(aqm\(aq: flags |= clone_newns; break; case \(aqn\(aq: flags |= clone_newnet; break; case \(aqp\(aq: flags |= clone_newpid; break; case \(aqu\(aq: flags |= clone_newuts; break; case \(aqv\(aq: verbose = 1; break; case \(aqz\(aq: map_zero = 1; break; case \(aqm\(aq: uid_map = optarg; break; case \(aqg\(aq: gid_map = optarg; break; case \(aqu\(aq: flags |= clone_newuser; break; default: usage(argv[0]); } } /* \-m or \-g without \-u is nonsensical */ if (((uid_map != null || gid_map != null || map_zero) && !(flags & clone_newuser)) || (map_zero && (uid_map != null || gid_map != null))) usage(argv[0]); args.argv = &argv[optind]; /* we use a pipe to synchronize the parent and child, in order to ensure that the parent sets the uid and gid maps before the child calls execve(). this ensures that the child maintains its capabilities during the execve() in the common case where we want to map the child\(aqs effective user id to 0 in the new user namespace. without this synchronization, the child would lose its capabilities if it performed an execve() with nonzero user ids (see the capabilities(7) man page for details of the transformation of a process\(aqs capabilities during execve()). */ if (pipe(args.pipe_fd) == \-1) errexit("pipe"); /* create the child in new namespace(s). */ child_pid = clone(childfunc, child_stack + stack_size, flags | sigchld, &args); if (child_pid == \-1) errexit("clone"); /* parent falls through to here. */ if (verbose) printf("%s: pid of child created by clone() is %jd\en", argv[0], (intmax_t) child_pid); /* update the uid and gid maps in the child. */ if (uid_map != null || map_zero) { snprintf(map_path, path_max, "/proc/%jd/uid_map", (intmax_t) child_pid); if (map_zero) { snprintf(map_buf, map_buf_size, "0 %jd 1", (intmax_t) getuid()); uid_map = map_buf; } update_map(uid_map, map_path); } if (gid_map != null || map_zero) { proc_setgroups_write(child_pid, "deny"); snprintf(map_path, path_max, "/proc/%jd/gid_map", (intmax_t) child_pid); if (map_zero) { snprintf(map_buf, map_buf_size, "0 %ld 1", (intmax_t) getgid()); gid_map = map_buf; } update_map(gid_map, map_path); } /* close the write end of the pipe, to signal to the child that we have updated the uid and gid maps. */ close(args.pipe_fd[1]); if (waitpid(child_pid, null, 0) == \-1) /* wait for child */ errexit("waitpid"); if (verbose) printf("%s: terminating\en", argv[0]); exit(exit_success); } .ee .sh see also .br newgidmap (1), \" from the shadow package .br newuidmap (1), \" from the shadow package .br clone (2), .br ptrace (2), .br setns (2), .br unshare (2), .br proc (5), .br subgid (5), \" from the shadow package .br subuid (5), \" from the shadow package .br capabilities (7), .br cgroup_namespaces (7), .br credentials (7), .br namespaces (7), .br pid_namespaces (7) .pp the kernel source file .ir documentation/admin\-guide/namespaces/resource\-control.rst . .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/clog2.3 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sat jul 24 19:17:53 1993 by rik faith (faith@cs.unc.edu) .th getusershell 3 2021-03-22 "gnu" "linux programmer's manual" .sh name getusershell, setusershell, endusershell \- get permitted user shells .sh synopsis .nf .b #include .pp .b char *getusershell(void); .b void setusershell(void); .b void endusershell(void); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br getusershell (), .br setusershell (), .br endusershell (): .nf since glibc 2.21: .\" commit 266865c0e7b79d4196e2cc393693463f03c90bd8 _default_source in glibc 2.19 and 2.20: _default_source || (_xopen_source && _xopen_source < 500) up to and including glibc 2.19: _bsd_source || (_xopen_source && _xopen_source < 500) .fi .sh description the .br getusershell () function returns the next line from the file .ir /etc/shells , opening the file if necessary. the line should contain the pathname of a valid user shell. if .i /etc/shells does not exist or is unreadable, .br getusershell () behaves as if .i /bin/sh and .i /bin/csh were listed in the file. .pp the .br setusershell () function rewinds .ir /etc/shells . .pp the .br endusershell () function closes .ir /etc/shells . .sh return value the .br getusershell () function returns null on end-of-file. .sh files .i /etc/shells .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br getusershell (), .br setusershell (), .br endusershell () t} thread safety mt-unsafe .te .hy .ad .sp 1 .sh conforming to 4.3bsd. .sh see also .br shells (5) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/select.2 .so man3/cexp2.3 .\" copyright (c) 2014 michael kerrisk .\" and copyright (c) 2014 peter zijlstra .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th sched_setattr 2 2021-03-22 "linux" "linux programmer's manual" .sh name sched_setattr, sched_getattr \- set and get scheduling policy and attributes .sh synopsis .nf .br "#include " " /* definition of " sched_* " constants */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "int syscall(sys_sched_setattr, pid_t " pid ", struct sched_attr *" attr , .bi " unsigned int " flags ); .bi "int syscall(sys_sched_getattr, pid_t " pid ", struct sched_attr *" attr , .bi " unsigned int " size ", unsigned int " flags ); .fi .\" fixme . add feature test macro requirements .pp .ir note : glibc provides no wrappers for these system calls, necessitating the use of .br syscall (2). .sh description .ss sched_setattr() the .br sched_setattr () system call sets the scheduling policy and associated attributes for the thread whose id is specified in .ir pid . if .i pid equals zero, the scheduling policy and attributes of the calling thread will be set. .pp currently, linux supports the following "normal" (i.e., non-real-time) scheduling policies as values that may be specified in .ir policy : .tp 14 .br sched_other the standard round-robin time-sharing policy; .\" in the 2.6 kernel sources, sched_other is actually called .\" sched_normal. .tp .br sched_batch for "batch" style execution of processes; and .tp .br sched_idle for running .i very low priority background jobs. .pp various "real-time" policies are also supported, for special time-critical applications that need precise control over the way in which runnable threads are selected for execution. for the rules governing when a process may use these policies, see .br sched (7). the real-time policies that may be specified in .ir policy are: .tp 14 .br sched_fifo a first-in, first-out policy; and .tp .br sched_rr a round-robin policy. .pp linux also provides the following policy: .tp 14 .b sched_deadline a deadline scheduling policy; see .br sched (7) for details. .pp the .i attr argument is a pointer to a structure that defines the new scheduling policy and attributes for the specified thread. this structure has the following form: .pp .in +4n .ex struct sched_attr { u32 size; /* size of this structure */ u32 sched_policy; /* policy (sched_*) */ u64 sched_flags; /* flags */ s32 sched_nice; /* nice value (sched_other, sched_batch) */ u32 sched_priority; /* static priority (sched_fifo, sched_rr) */ /* remaining fields are for sched_deadline */ u64 sched_runtime; u64 sched_deadline; u64 sched_period; }; .ee .in .pp the fields of the .ir sched_attr structure are as follows: .tp .b size this field should be set to the size of the structure in bytes, as in .ir "sizeof(struct sched_attr)" . if the provided structure is smaller than the kernel structure, any additional fields are assumed to be '0'. if the provided structure is larger than the kernel structure, the kernel verifies that all additional fields are 0; if they are not, .br sched_setattr () fails with the error .br e2big and updates .i size to contain the size of the kernel structure. .ip the above behavior when the size of the user-space .i sched_attr structure does not match the size of the kernel structure allows for future extensibility of the interface. malformed applications that pass oversize structures won't break in the future if the size of the kernel .i sched_attr structure is increased. in the future, it could also allow applications that know about a larger user-space .i sched_attr structure to determine whether they are running on an older kernel that does not support the larger structure. .tp .i sched_policy this field specifies the scheduling policy, as one of the .br sched_* values listed above. .tp .i sched_flags this field contains zero or more of the following flags that are ored together to control scheduling behavior: .rs .tp .br sched_flag_reset_on_fork children created by .br fork (2) do not inherit privileged scheduling policies. see .br sched (7) for details. .tp .br sched_flag_reclaim " (since linux 4.13)" .\" 2d4283e9d583a3ee8cfb1cbb9c1270614df4c29d this flag allows a .br sched_deadline thread to reclaim bandwidth unused by other real-time threads. .\" bandwidth reclaim is done via the grub algorithm; see .\" documentation/scheduler/sched-deadline.txt .tp .br sched_flag_dl_overrun " (since linux 4.16)" .\" commit 34be39305a77b8b1ec9f279163c7cdb6cc719b91 this flag allows an application to get informed about run-time overruns in .br sched_deadline threads. such overruns may be caused by (for example) coarse execution time accounting or incorrect parameter assignment. notification takes the form of a .b sigxcpu signal which is generated on each overrun. .ip this .br sigxcpu signal is .i process-directed (see .br signal (7)) rather than thread-directed. this is probably a bug. on the one hand, .br sched_setattr () is being used to set a per-thread attribute. on the other hand, if the process-directed signal is delivered to a thread inside the process other than the one that had a run-time overrun, the application has no way of knowing which thread overran. .re .tp .i sched_nice this field specifies the nice value to be set when specifying .ir sched_policy as .br sched_other or .br sched_batch . the nice value is a number in the range \-20 (high priority) to +19 (low priority); see .br sched (7). .tp .i sched_priority this field specifies the static priority to be set when specifying .ir sched_policy as .br sched_fifo or .br sched_rr . the allowed range of priorities for these policies can be determined using .br sched_get_priority_min (2) and .br sched_get_priority_max (2). for other policies, this field must be specified as 0. .tp .i sched_runtime this field specifies the "runtime" parameter for deadline scheduling. the value is expressed in nanoseconds. this field, and the next two fields, are used only for .br sched_deadline scheduling; for further details, see .br sched (7). .tp .i sched_deadline this field specifies the "deadline" parameter for deadline scheduling. the value is expressed in nanoseconds. .tp .i sched_period this field specifies the "period" parameter for deadline scheduling. the value is expressed in nanoseconds. .pp the .i flags argument is provided to allow for future extensions to the interface; in the current implementation it must be specified as 0. .\" .\" .ss sched_getattr() the .br sched_getattr () system call fetches the scheduling policy and the associated attributes for the thread whose id is specified in .ir pid . if .i pid equals zero, the scheduling policy and attributes of the calling thread will be retrieved. .pp the .i size argument should be set to the size of the .i sched_attr structure as known to user space. the value must be at least as large as the size of the initially published .i sched_attr structure, or the call fails with the error .br einval . .pp the retrieved scheduling attributes are placed in the fields of the .i sched_attr structure pointed to by .ir attr . the kernel sets .i attr.size to the size of its .i sched_attr structure. .pp if the caller-provided .i attr buffer is larger than the kernel's .i sched_attr structure, the additional bytes in the user-space structure are not touched. if the caller-provided structure is smaller than the kernel .i sched_attr structure, the kernel will silently not return any values which would be stored outside the provided space. as with .br sched_setattr (), these semantics allow for future extensibility of the interface. .pp the .i flags argument is provided to allow for future extensions to the interface; in the current implementation it must be specified as 0. .sh return value on success, .br sched_setattr () and .br sched_getattr () return 0. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .br sched_getattr () and .br sched_setattr () can both fail for the following reasons: .tp .b einval .i attr is null; or .i pid is negative; or .i flags is not zero. .tp .b esrch the thread whose id is .i pid could not be found. .pp in addition, .br sched_getattr () can fail for the following reasons: .tp .b e2big the buffer specified by .i size and .i attr is too small. .tp .b einval .i size is invalid; that is, it is smaller than the initial version of the .i sched_attr structure (48 bytes) or larger than the system page size. .pp in addition, .br sched_setattr () can fail for the following reasons: .tp .b e2big the buffer specified by .i size and .i attr is larger than the kernel structure, and one or more of the excess bytes is nonzero. .tp .b ebusy .b sched_deadline admission control failure, see .br sched (7). .tp .b einval .i attr.sched_policy is not one of the recognized policies; .i attr.sched_flags contains a flag other than .br sched_flag_reset_on_fork ; or .i attr.sched_priority is invalid; or .i attr.sched_policy is .br sched_deadline and the deadline scheduling parameters in .i attr are invalid. .tp .b eperm the caller does not have appropriate privileges. .tp .b eperm the cpu affinity mask of the thread specified by .i pid does not include all cpus in the system (see .br sched_setaffinity (2)). .sh versions these system calls first appeared in linux 3.14. .\" fixme . add glibc version .sh conforming to these system calls are nonstandard linux extensions. .sh notes glibc does not provide wrappers for these system calls; call them using .br syscall (2). .pp .br sched_setattr () provides a superset of the functionality of .br sched_setscheduler (2), .br sched_setparam (2), .br nice (2), and (other than the ability to set the priority of all processes belonging to a specified user or all processes in a specified group) .br setpriority (2). analogously, .br sched_getattr () provides a superset of the functionality of .br sched_getscheduler (2), .br sched_getparam (2), and (partially) .br getpriority (2). .sh bugs in linux versions up to .\" fixme . patch sent to peter zijlstra 3.15, .br sched_setattr () failed with the error .br efault instead of .br e2big for the case described in errors. .pp in linux versions up to 5.3, .br sched_getattr () failed with the error .br efbig if the in-kernel .ir sched_attr structure was larger than the .ir size passed by user space. .\" in linux versions up to up 3.15, .\" fixme . patch from peter zijlstra pending .\" .br sched_setattr () .\" allowed a negative .\" .i attr.sched_policy .\" value. .sh see also .ad l .nh .br chrt (1), .br nice (2), .br sched_get_priority_max (2), .br sched_get_priority_min (2), .br sched_getaffinity (2), .br sched_getparam (2), .br sched_getscheduler (2), .br sched_rr_get_interval (2), .br sched_setaffinity (2), .br sched_setparam (2), .br sched_setscheduler (2), .br sched_yield (2), .br setpriority (2), .br pthread_getschedparam (3), .br pthread_setschedparam (3), .br pthread_setschedprio (3), .br capabilities (7), .br cpuset (7), .br sched (7) .ad .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2001 andries brouwer . .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th unlocked_stdio 3 2021-03-22 "" "linux programmer's manual" .sh name getc_unlocked, getchar_unlocked, putc_unlocked, putchar_unlocked \- nonlocking stdio functions .sh synopsis .nf .b #include .pp .bi "int getc_unlocked(file *" stream ); .b "int getchar_unlocked(void);" .bi "int putc_unlocked(int " c ", file *" stream ); .bi "int putchar_unlocked(int " c ); .pp .bi "void clearerr_unlocked(file *" stream ); .bi "int feof_unlocked(file *" stream ); .bi "int ferror_unlocked(file *" stream ); .bi "int fileno_unlocked(file *" stream ); .bi "int fflush_unlocked(file *" stream ); .pp .bi "int fgetc_unlocked(file *" stream ); .bi "int fputc_unlocked(int " c ", file *" stream ); .pp .bi "size_t fread_unlocked(void *restrict " ptr ", size_t " size ", size_t " n , .bi " file *restrict " stream ); .bi "size_t fwrite_unlocked(const void *restrict " ptr ", size_t " size \ ", size_t " n , .bi " file *restrict " stream ); .pp .bi "char *fgets_unlocked(char *restrict " s ", int " n \ ", file *restrict " stream ); .bi "int fputs_unlocked(const char *restrict " s ", file *restrict " stream ); .pp .b #include .pp .bi "wint_t getwc_unlocked(file *" stream ); .b "wint_t getwchar_unlocked(void);" .bi "wint_t fgetwc_unlocked(file *" stream ); .pp .bi "wint_t fputwc_unlocked(wchar_t " wc ", file *" stream ); .bi "wint_t putwc_unlocked(wchar_t " wc ", file *" stream ); .bi "wint_t putwchar_unlocked(wchar_t " wc ); .pp .bi "wchar_t *fgetws_unlocked(wchar_t *restrict " ws ", int " n , .bi " file *restrict " stream ); .bi "int fputws_unlocked(const wchar_t *restrict " ws , .bi " file *restrict " stream ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .nh .re .ad l .pp .br getc_unlocked (), .br getchar_unlocked (), .br putc_unlocked (), .br putchar_unlocked (): .nf /* since glibc 2.24: */ _posix_c_source >= 199309l || /* glibc <= 2.23: */ _posix_c_source || /* glibc <= 2.19: */ _svid_source || _bsd_source .fi .pp .br clearerr_unlocked (), .br feof_unlocked (), .br ferror_unlocked (), .br fileno_unlocked (), .br fflush_unlocked (), .br fgetc_unlocked (), .br fputc_unlocked (), .br fread_unlocked (), .br fwrite_unlocked (): .nf /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _svid_source || _bsd_source .fi .pp .br fgets_unlocked (), .br fputs_unlocked (), .br getwc_unlocked (), .br getwchar_unlocked (), .br fgetwc_unlocked (), .br fputwc_unlocked (), .br putwchar_unlocked (), .br fgetws_unlocked (), .br fputws_unlocked (): .nf _gnu_source .fi .hy .ad .sh description each of these functions has the same behavior as its counterpart without the "_unlocked" suffix, except that they do not use locking (they do not set locks themselves, and do not test for the presence of locks set by others) and hence are thread-unsafe. see .br flockfile (3). .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lb lb lbx l l l. interface attribute value t{ .br getc_unlocked (), .br putc_unlocked (), .br clearerr_unlocked (), .br fflush_unlocked (), .br fgetc_unlocked (), .br fputc_unlocked (), .br fread_unlocked (), .br fwrite_unlocked (), .br fgets_unlocked (), .br fputs_unlocked (), .br getwc_unlocked (), .br fgetwc_unlocked (), .br fputwc_unlocked (), .br putwc_unlocked (), .br fgetws_unlocked (), .br fputws_unlocked () t} thread safety t{ mt-safe race:stream t} t{ .br getchar_unlocked (), .br getwchar_unlocked () t} thread safety t{ mt-unsafe race:stdin t} t{ .br putchar_unlocked (), .br putwchar_unlocked () t} thread safety t{ mt-unsafe race:stdout t} t{ .br feof_unlocked (), .br ferror_unlocked (), .br fileno_unlocked () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to the four functions .br getc_unlocked (), .br getchar_unlocked (), .br putc_unlocked (), .br putchar_unlocked () are in posix.1-2001 and posix.1-2008. .pp the nonstandard .br *_unlocked () variants occur on a few unix systems, and are available in recent glibc. .\" e.g., in hp-ux 10.0. in hp-ux 10.30 they are called obsolescent, and .\" moved to a compatibility library. .\" available in hp-ux 10.0: clearerr_unlocked, fclose_unlocked, .\" feof_unlocked, ferror_unlocked, fflush_unlocked, fgets_unlocked, .\" fgetwc_unlocked, fgetws_unlocked, fileno_unlocked, fputs_unlocked, .\" fputwc_unlocked, fputws_unlocked, fread_unlocked, fseek_unlocked, .\" ftell_unlocked, fwrite_unlocked, getc_unlocked, getchar_unlocked, .\" getw_unlocked, getwc_unlocked, getwchar_unlocked, putc_unlocked, .\" putchar_unlocked, puts_unlocked, putws_unlocked, putw_unlocked, .\" putwc_unlocked, putwchar_unlocked, rewind_unlocked, setvbuf_unlocked, .\" ungetc_unlocked, ungetwc_unlocked. they should probably not be used. .sh see also .br flockfile (3), .br stdio (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/nextafter.3 .so man3/index.3 .so man3/trunc.3 .\" copyright (c) 2006 by michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" 2008-06-24, mtk: added some details about where jiffies come into .\" play; added section on high-resolution timers. .\" .th time 7 2020-04-11 "linux" "linux programmer's manual" .sh name time \- overview of time and timers .sh description .ss real time and process time .i "real time" is defined as time measured from some fixed point, either from a standard point in the past (see the description of the epoch and calendar time below), or from some point (e.g., the start) in the life of a process .ri ( "elapsed time" ). .pp .i "process time" is defined as the amount of cpu time used by a process. this is sometimes divided into .i user and .i system components. user cpu time is the time spent executing code in user mode. system cpu time is the time spent by the kernel executing in system mode on behalf of the process (e.g., executing system calls). the .br time (1) command can be used to determine the amount of cpu time consumed during the execution of a program. a program can determine the amount of cpu time it has consumed using .br times (2), .br getrusage (2), or .br clock (3). .ss the hardware clock most computers have a (battery-powered) hardware clock which the kernel reads at boot time in order to initialize the software clock. for further details, see .br rtc (4) and .br hwclock (8). .ss the software clock, hz, and jiffies the accuracy of various system calls that set timeouts, (e.g., .br select (2), .br sigtimedwait (2)) .\" semtimedop(), mq_timedwait(), io_getevents(), poll() are the same .\" futexes and thus sem_timedwait() seem to use high-res timers. and measure cpu time (e.g., .br getrusage (2)) is limited by the resolution of the .ir "software clock" , a clock maintained by the kernel which measures time in .ir jiffies . the size of a jiffy is determined by the value of the kernel constant .ir hz . .pp the value of .i hz varies across kernel versions and hardware platforms. on i386 the situation is as follows: on kernels up to and including 2.4.x, hz was 100, giving a jiffy value of 0.01 seconds; starting with 2.6.0, hz was raised to 1000, giving a jiffy of 0.001 seconds. since kernel 2.6.13, the hz value is a kernel configuration parameter and can be 100, 250 (the default) or 1000, yielding a jiffies value of, respectively, 0.01, 0.004, or 0.001 seconds. since kernel 2.6.20, a further frequency is available: 300, a number that divides evenly for the common video frame rates (pal, 25 hz; ntsc, 30 hz). .pp the .br times (2) system call is a special case. it reports times with a granularity defined by the kernel constant .ir user_hz . user-space applications can determine the value of this constant using .ir sysconf(_sc_clk_tck) . .\" glibc gets this info with a little help from the elf loader; .\" see glibc elf/dl-support.c and kernel fs/binfmt_elf.c. .\" .ss system and process clocks; time namespaces the kernel supports a range of clocks that measure various kinds of elapsed and virtual (i.e., consumed cpu) time. these clocks are described in .br clock_gettime (2). a few of the clocks are settable using .br clock_settime (2). the values of certain clocks are virtualized by time namespaces; see .br time_namespaces (7). .\" .ss high-resolution timers before linux 2.6.21, the accuracy of timer and sleep system calls (see below) was also limited by the size of the jiffy. .pp since linux 2.6.21, linux supports high-resolution timers (hrts), optionally configurable via .br config_high_res_timers . on a system that supports hrts, the accuracy of sleep and timer system calls is no longer constrained by the jiffy, but instead can be as accurate as the hardware allows (microsecond accuracy is typical of modern hardware). you can determine whether high-resolution timers are supported by checking the resolution returned by a call to .br clock_getres (2) or looking at the "resolution" entries in .ir /proc/timer_list . .pp hrts are not supported on all hardware architectures. (support is provided on x86, arm, and powerpc, among others.) .ss the epoch unix systems represent time in seconds since the .ir epoch , 1970-01-01 00:00:00 +0000 (utc). .pp a program can determine the .i "calendar time" via the .br clock_gettime (2) .br clock_realtime clock, which returns time (in seconds and nanoseconds) that have elapsed since the epoch; .br time (2) provides similar information, but only with accuracy to the nearest second. the system time can be changed using .br clock_settime (2). .\" .ss broken-down time certain library functions use a structure of type .i tm to represent .ir "broken-down time" , which stores time value separated out into distinct components (year, month, day, hour, minute, second, etc.). this structure is described in .br ctime (3), which also describes functions that convert between calendar time and broken-down time. functions for converting between broken-down time and printable string representations of the time are described in .br ctime (3), .br strftime (3), and .br strptime (3). .ss sleeping and setting timers various system calls and functions allow a program to sleep (suspend execution) for a specified period of time; see .br nanosleep (2), .br clock_nanosleep (2), and .br sleep (3). .pp various system calls allow a process to set a timer that expires at some point in the future, and optionally at repeated intervals; see .br alarm (2), .br getitimer (2), .br timerfd_create (2), and .br timer_create (2). .ss timer slack since linux 2.6.28, it is possible to control the "timer slack" value for a thread. the timer slack is the length of time by which the kernel may delay the wake-up of certain system calls that block with a timeout. permitting this delay allows the kernel to coalesce wake-up events, thus possibly reducing the number of system wake-ups and saving power. for more details, see the description of .b pr_set_timerslack in .br prctl (2). .sh see also .ad l .nh .br date (1), .br time (1), .br timeout (1), .br adjtimex (2), .br alarm (2), .br clock_gettime (2), .br clock_nanosleep (2), .br getitimer (2), .br getrlimit (2), .br getrusage (2), .br gettimeofday (2), .br nanosleep (2), .br stat (2), .br time (2), .br timer_create (2), .br timerfd_create (2), .br times (2), .br utime (2), .br adjtime (3), .br clock (3), .br clock_getcpuclockid (3), .br ctime (3), .br ntp_adjtime (3), .br ntp_gettime (3), .br pthread_getcpuclockid (3), .br sleep (3), .br strftime (3), .br strptime (3), .br timeradd (3), .br usleep (3), .br rtc (4), .br time_namespaces (7), .br hwclock (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. #!/bin/sh # # render man pages with fixmes shown as tables # in the rendered page # for f in $*; do cat $f | awk ' /^\.\\" *fixme/ { if ($0 ~ /.*fixme *\..*/) { # fixmes of the form "fixme ." are "private" and # ignored by this script } else { sub("fixme[: ]*", "") if ($0 ~ /^\.\\"[ ]*$/) { # if the fixme line contains no additional text after # "fixme", then discard the blank line getline } print "" if (fixme == 0) { print ".ts" print ".allbox;" print "lbw52" print "l." print "fixme" print "t{" } fixme = 1 } } $0 !~ /^\.\\"/ && fixme == 1 { fixme = 0 print "t}" print ".te" print "" } fixme == 1 { sub("^\\...[ ]", "") sub("^\\...", "") gsub("'"'"'", "\\(aq") if ($0 ~ /^[ ][ ]*.*/) { print ".br" sub("^[ ]*", " ") } } { print $0 } ' | tee "/tmp/$(basename $f).src" | man --nh --nj -l /dev/stdin done .so man3/fseek.3 .so man3/cpu_set.3 .so man3/__ppc_set_ppr_med.3 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" gnu texinfo documentation on glibc date/time functions. .\" modified sat jul 24 18:03:44 1993 by rik faith (faith@cs.unc.edu) .\" applied fix by wolfgang franke, aeb, 961011 .\" corrected return value, aeb, 970307 .\" added single unix spec conversions and %z, aeb/esr, 990329. .\" 2005-11-22 mtk, added glibc notes covering optional 'flag' and .\" 'width' components of conversion specifications. .\" .th strftime 3 2021-03-22 "gnu" "linux programmer's manual" .sh name strftime \- format date and time .sh synopsis .nf .b #include .pp .bi "size_t strftime(char *restrict " s ", size_t " max , .bi " const char *restrict " format , .bi " const struct tm *restrict " tm ); .fi .sh description the .br strftime () function formats the broken-down time .i tm according to the format specification .i format and places the result in the character array .i s of size .ir max . the broken-down time structure .i tm is defined in .ir . see also .br ctime (3). .\" fixme . posix says: local timezone information is used as though .\" strftime() called tzset(). but this doesn't appear to be the case .pp the format specification is a null-terminated string and may contain special character sequences called .ir "conversion specifications", each of which is introduced by a \(aq%\(aq character and terminated by some other character known as a .ir "conversion specifier character". all other character sequences are .ir "ordinary character sequences". .pp the characters of ordinary character sequences (including the null byte) are copied verbatim from .i format to .ir s . however, the characters of conversion specifications are replaced as shown in the list below. in this list, the field(s) employed from the .i tm structure are also shown. .tp .b %a the abbreviated name of the day of the week according to the current locale. (calculated from .ir tm_wday .) (the specific names used in the current locale can be obtained by calling .br nl_langinfo (3) with .br abday_ { 1 \(en 7 } as an argument.) .tp .b %a the full name of the day of the week according to the current locale. (calculated from .ir tm_wday .) (the specific names used in the current locale can be obtained by calling .br nl_langinfo (3) with .br day_ { 1 \(en 7 } as an argument.) .tp .b %b the abbreviated month name according to the current locale. (calculated from .ir tm_mon .) (the specific names used in the current locale can be obtained by calling .br nl_langinfo (3) with .br abmon_ { 1 \(en 12 } as an argument.) .tp .b %b the full month name according to the current locale. (calculated from .ir tm_mon .) (the specific names used in the current locale can be obtained by calling .br nl_langinfo (3) with .br mon_ { 1 \(en 12 } as an argument.) .tp .b %c the preferred date and time representation for the current locale. (the specific format used in the current locale can be obtained by calling .br nl_langinfo (3) with .b d_t_fmt as an argument for the .b %c conversion specification, and with .b era_d_t_fmt for the .b %ec conversion specification.) (in the posix locale this is equivalent to .br "%a %b %e %h:%m:%s %y" .) .tp .b %c the century number (year/100) as a 2-digit integer. (su) (the .b %ec conversion specification corresponds to the name of the era.) (calculated from .ir tm_year .) .tp .b %d the day of the month as a decimal number (range 01 to 31). (calculated from .ir tm_mday .) .tp .b %d equivalent to .br %m/%d/%y . (yecch\(emfor americans only. americans should note that in other countries .b %d/%m/%y is rather common. this means that in international context this format is ambiguous and should not be used.) (su) .tp .b %e like .br %d , the day of the month as a decimal number, but a leading zero is replaced by a space. (su) (calculated from .ir tm_mday .) .tp .b %e modifier: use alternative ("era-based") format, see below. (su) .tp .b %f equivalent to .b %y\-%m\-%d (the iso\ 8601 date format). (c99) .tp .b %g the iso\ 8601 week-based year (see notes) with century as a decimal number. the 4-digit year corresponding to the iso week number (see .br %v ). this has the same format and value as .br %y , except that if the iso week number belongs to the previous or next year, that year is used instead. (tz) (calculated from .ir tm_year , .ir tm_yday , and .ir tm_wday .) .tp .b %g like .br %g , but without century, that is, with a 2-digit year (00\(en99). (tz) (calculated from .ir tm_year , .ir tm_yday , and .ir tm_wday .) .tp .b %h equivalent to .br %b . (su) .tp .b %h the hour as a decimal number using a 24-hour clock (range 00 to 23). (calculated from .ir tm_hour .) .tp .b %i the hour as a decimal number using a 12-hour clock (range 01 to 12). (calculated from .ir tm_hour .) .tp .b %j the day of the year as a decimal number (range 001 to 366). (calculated from .ir tm_yday .) .tp .b %k the hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank. (see also .br %h .) (calculated from .ir tm_hour .) (tz) .tp .b %l the hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank. (see also .br %i .) (calculated from .ir tm_hour .) (tz) .tp .b %m the month as a decimal number (range 01 to 12). (calculated from .ir tm_mon .) .tp .b %m the minute as a decimal number (range 00 to 59). (calculated from .ir tm_min .) .tp .b %n a newline character. (su) .tp .b %o modifier: use alternative numeric symbols, see below. (su) .tp .b %p either "am" or "pm" according to the given time value, or the corresponding strings for the current locale. noon is treated as "pm" and midnight as "am". (calculated from .ir tm_hour .) (the specific string representations used for "am" and "pm" in the current locale can be obtained by calling .br nl_langinfo (3) with .br am_str " and " pm_str , respectively.) .tp .b %p like .b %p but in lowercase: "am" or "pm" or a corresponding string for the current locale. (calculated from .ir tm_hour .) (gnu) .tp .b %r the time in a.m. or p.m. notation. (su) (the specific format used in the current locale can be obtained by calling .br nl_langinfo (3) with .b t_fmt_ampm as an argument.) (in the posix locale this is equivalent to .br "%i:%m:%s %p" .) .tp .b %r the time in 24-hour notation .rb ( %h:%m ). (su) for a version including the seconds, see .b %t below. .tp .b %s the number of seconds since the epoch, 1970-01-01 00:00:00 +0000 (utc). (tz) (calculated from .ir mktime(tm) .) .tp .b %s the second as a decimal number (range 00 to 60). (the range is up to 60 to allow for occasional leap seconds.) (calculated from .ir tm_sec .) .tp .b %t a tab character. (su) .tp .b %t the time in 24-hour notation .rb ( %h:%m:%s ). (su) .tp .b %u the day of the week as a decimal, range 1 to 7, monday being 1. see also .br %w . (calculated from .ir tm_wday .) (su) .tp .b %u the week number of the current year as a decimal number, range 00 to 53, starting with the first sunday as the first day of week 01. see also .b %v and .br %w . (calculated from .ir tm_yday and .ir tm_wday .) .tp .b %v the iso\ 8601 week number (see notes) of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days in the new year. see also .b %u and .br %w . (calculated from .ir tm_year , .ir tm_yday , and .ir tm_wday .) (su) .tp .b %w the day of the week as a decimal, range 0 to 6, sunday being 0. see also .br %u . (calculated from .ir tm_wday .) .tp .b %w the week number of the current year as a decimal number, range 00 to 53, starting with the first monday as the first day of week 01. (calculated from .ir tm_yday and .ir tm_wday .) .tp .b %x the preferred date representation for the current locale without the time. (the specific format used in the current locale can be obtained by calling .br nl_langinfo (3) with .b d_fmt as an argument for the .b %x conversion specification, and with .b era_d_fmt for the .b %ex conversion specification.) (in the posix locale this is equivalent to .br %m/%d/%y .) .tp .b %x the preferred time representation for the current locale without the date. (the specific format used in the current locale can be obtained by calling .br nl_langinfo (3) with .b t_fmt as an argument for the .b %x conversion specification, and with .b era_t_fmt for the .b %ex conversion specification.) (in the posix locale this is equivalent to .br %h:%m:%s .) .tp .b %y the year as a decimal number without a century (range 00 to 99). (the .b %ey conversion specification corresponds to the year since the beginning of the era denoted by the .b %ec conversion specification.) (calculated from .ir tm_year ) .tp .b %y the year as a decimal number including the century. (the .b %ey conversion specification corresponds to the full alternative year representation.) (calculated from .ir tm_year ) .tp .b %z the .i +hhmm or .i \-hhmm numeric timezone (that is, the hour and minute offset from utc). (su) .tp .b %z the timezone name or abbreviation. .tp .b %+ .\" nov 05 -- not in linux/glibc, but is in some bsds (according to .\" their man pages) the date and time in .br date (1) format. (tz) (not supported in glibc2.) .tp .b %% a literal \(aq%\(aq character. .pp some conversion specifications can be modified by preceding the conversion specifier character by the .b e or .b o .i modifier to indicate that an alternative format should be used. if the alternative format or specification does not exist for the current locale, the behavior will be as if the unmodified conversion specification were used. (su) the single unix specification mentions .br %ec , .br %ec , .br %ex , .br %ex , .br %ey , .br %ey , .br %od , .br %oe , .br %oh , .br %oi , .br %om , .br %om , .br %os , .br %ou , .br %ou , .br %ov , .br %ow , .br %ow , .br %oy , where the effect of the .b o modifier is to use alternative numeric symbols (say, roman numerals), and that of the .b e modifier is to use a locale-dependent alternative representation. the rules governing date representation with the .b e modifier can be obtained by supplying .b era as an argument to a .br nl_langinfo (3). one example of such alternative forms is the japanese era calendar scheme in the .b ja_jp glibc locale. .sh return value provided that the result string, including the terminating null byte, does not exceed .i max bytes, .br strftime () returns the number of bytes (excluding the terminating null byte) placed in the array .ir s . if the length of the result string (including the terminating null byte) would exceed .i max bytes, then .br strftime () returns 0, and the contents of the array are undefined. .\" (this behavior applies since at least libc 4.4.4; .\" very old versions of libc, such as libc 4.4.1, .\" would return .\" .i max .\" if the array was too small.) .pp note that the return value 0 does not necessarily indicate an error. for example, in many locales .b %p yields an empty string. an empty .i format string will likewise yield an empty string. .sh environment the environment variables .b tz and .b lc_time are used. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br strftime () t} thread safety mt-safe env locale .te .hy .ad .sp 1 .sh conforming to svr4, c89, c99. .\" fixme strftime() is in posix.1-2001 and posix.1-2008, but the details .\" in the standards changed across versions. investigate and .\" write up. there are strict inclusions between the set of conversions given in ansi c (unmarked), those given in the single unix specification (marked su), those given in olson's timezone package (marked tz), and those given in glibc (marked gnu), except that .b %+ is not supported in glibc2. on the other hand glibc2 has several more extensions. posix.1 only refers to ansi c; posix.2 describes under .br date (1) several extensions that could apply to .br strftime () as well. the .b %f conversion is in c99 and posix.1-2001. .pp in susv2, the .b %s specifier allowed a range of 00 to 61, to allow for the theoretical possibility of a minute that included a double leap second (there never has been such a minute). .sh notes .ss iso 8601 week dates .br %g , .br %g , and .br %v yield values calculated from the week-based year defined by the iso\ 8601 standard. in this system, weeks start on a monday, and are numbered from 01, for the first week, up to 52 or 53, for the last week. week 1 is the first week where four or more days fall within the new year (or, synonymously, week 01 is: the first week of the year that contains a thursday; or, the week that has 4 january in it). when three or fewer days of the first calendar week of the new year fall within that year, then the iso 8601 week-based system counts those days as part of week 52 or 53 of the preceding year. for example, 1 january 2010 is a friday, meaning that just three days of that calendar week fall in 2010. thus, the iso\ 8601 week-based system considers these days to be part of week 53 .rb ( %v ) of the year 2009 .rb ( %g ); week 01 of iso\ 8601 year 2010 starts on monday, 4 january 2010. similarly, the first two days of january 2011 are considered to be part of week 52 of the year 2010. .ss glibc notes glibc provides some extensions for conversion specifications. (these extensions are not specified in posix.1-2001, but a few other systems provide similar features.) .\" hp-ux and tru64 also have features like this. between the \(aq%\(aq character and the conversion specifier character, an optional .i flag and field .i width may be specified. (these precede the .b e or .b o modifiers, if present.) .pp the following flag characters are permitted: .tp .b _ (underscore) pad a numeric result string with spaces. .tp .b \- (dash) do not pad a numeric result string. .tp .b 0 pad a numeric result string with zeros even if the conversion specifier character uses space-padding by default. .tp .b \(ha convert alphabetic characters in result string to uppercase. .tp .b # swap the case of the result string. (this flag works only with certain conversion specifier characters, and of these, it is only really useful with .br %z .) .pp an optional decimal width specifier may follow the (possibly absent) flag. if the natural size of the field is smaller than this width, then the result string is padded (on the left) to the specified width. .sh bugs if the output string would exceed .i max bytes, .i errno is .i not set. this makes it impossible to distinguish this error case from cases where the .i format string legitimately produces a zero-length output string. posix.1-2001 does .i not specify any .i errno settings for .br strftime (). .pp some buggy versions of .br gcc (1) complain about the use of .br %c : .ir "warning: \`%c\(aq yields only last 2 digits of year in some locales" . of course programmers are encouraged to use .br %c , as it gives the preferred date and time representation. one meets all kinds of strange obfuscations to circumvent this .br gcc (1) problem. a relatively clean one is to add an intermediate function .pp .in +4n .ex size_t my_strftime(char *s, size_t max, const char *fmt, const struct tm *tm) { return strftime(s, max, fmt, tm); } .ee .in .pp nowadays, .br gcc (1) provides the .ir \-wno\-format\-y2k option to prevent the warning, so that the above workaround is no longer required. .sh examples .br "rfc\ 2822-compliant date format" (with an english locale for %a and %b) .pp .in +4n .ex "%a,\ %d\ %b\ %y\ %t\ %z" .ee .in .pp .br "rfc\ 822-compliant date format" (with an english locale for %a and %b) .pp .in +4n .ex "%a,\ %d\ %b\ %y\ %t\ %z" .ee .in .ss example program the program below can be used to experiment with .br strftime (). .pp some examples of the result string produced by the glibc implementation of .br strftime () are as follows: .pp .in +4n .ex .rb "$" " ./a.out \(aq%m\(aq" result string is "11" .rb "$" " ./a.out \(aq%5m\(aq" result string is "00011" .rb "$" " ./a.out \(aq%_5m\(aq" result string is " 11" .ee .in .ss program source \& .ex #include #include #include int main(int argc, char *argv[]) { char outstr[200]; time_t t; struct tm *tmp; t = time(null); tmp = localtime(&t); if (tmp == null) { perror("localtime"); exit(exit_failure); } if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) { fprintf(stderr, "strftime returned 0"); exit(exit_failure); } printf("result string is \e"%s\e"\en", outstr); exit(exit_success); } .ee .sh see also .br date (1), .br time (2), .br ctime (3), .br nl_langinfo (3), .br setlocale (3), .br sprintf (3), .br strptime (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/xdr.3 .so man3/mq_open.3 .\" because mq_open(3) is layered on a system call of the same name .so man3/hsearch.3 .\" copyright (c) 2012 by michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th malloc_trim 3 2021-03-22 "linux" "linux programmer's manual" .sh name malloc_trim \- release free memory from the heap .sh synopsis .nf .b #include .pp .bi "int malloc_trim(size_t " pad ); .fi .sh description the .br malloc_trim () function attempts to release free memory from the heap (by calling .br sbrk (2) or .br madvise (2) with suitable arguments). .pp the .i pad argument specifies the amount of free space to leave untrimmed at the top of the heap. if this argument is 0, only the minimum amount of memory is maintained at the top of the heap (i.e., one page or less). a nonzero argument can be used to maintain some trailing space at the top of the heap in order to allow future allocations to be made without having to extend the heap with .br sbrk (2). .sh return value the .br malloc_trim () function returns 1 if memory was actually released back to the system, or 0 if it was not possible to release any memory. .sh errors no errors are defined. .\" .sh versions .\" available already in glibc 2.0, possibly earlier .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br malloc_trim () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to this function is a gnu extension. .sh notes only the main heap (using .br sbrk (2)) honors the .i pad argument; thread heaps do not. .pp since glibc 2.8 this function frees memory in all arenas and in all chunks with whole free pages. .\" see commit 68631c8eb92ff38d9da1ae34f6aa048539b199cc .\" (dated 2007-12-16) which adds iteration over all .\" arenas and frees all pages in chunks which are free. .pp before glibc 2.8 this function only freed memory at the top of the heap in the main arena. .sh see also .br sbrk (2), .br malloc (3), .br mallopt (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/gethostbyname.3 .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th iswblank 3 2021-03-22 "gnu" "linux programmer's manual" .sh name iswblank \- test for whitespace wide character .sh synopsis .nf .b #include .pp .bi "int iswblank(wint_t " wc ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br iswblank (): .nf _isoc99_source || _posix_c_source >= 200112l .fi .sh description the .br iswblank () function is the wide-character equivalent of the .br isblank (3) function. it tests whether \fiwc\fp is a wide character belonging to the wide-character class "blank". .pp the wide-character class "blank" is a subclass of the wide-character class "space". .pp being a subclass of the wide-character class "space", the wide-character class "blank" is disjoint from the wide-character class "graph" and therefore also disjoint from its subclasses "alnum", "alpha", "upper", "lower", "digit", "xdigit", "punct". .pp the wide-character class "blank" always contains at least the space character and the control character \(aq\et\(aq. .sh return value the .br iswblank () function returns nonzero if \fiwc\fp is a wide character belonging to the wide-character class "blank". otherwise, it returns zero. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br iswblank () t} thread safety mt-safe locale .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes the behavior of .br iswblank () depends on the .b lc_ctype category of the current locale. .sh see also .br isblank (3), .br iswctype (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/strfmon.3 .so man3/tailq.3 .\" copyright (c) 2001 andries brouwer . .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th setlogmask 3 2021-03-22 "" "linux programmer's manual" .sh name setlogmask \- set log priority mask .sh synopsis .nf .b #include .pp .bi "int setlogmask(int " mask ); .fi .sh description a process has a log priority mask that determines which calls to .br syslog (3) may be logged. all other calls will be ignored. logging is enabled for the priorities that have the corresponding bit set in .ir mask . the initial mask is such that logging is enabled for all priorities. .pp the .br setlogmask () function sets this logmask for the calling process, and returns the previous mask. if the mask argument is 0, the current logmask is not modified. .pp the eight priorities are .br log_emerg , .br log_alert , .br log_crit , .br log_err , .br log_warning , .br log_notice , .br log_info , and .br log_debug . the bit corresponding to a priority .i p is .ir log_mask(p) . some systems also provide a macro .ir log_upto(p) for the mask of all priorities in the above list up to and including .ir p . .sh return value this function returns the previous log priority mask. .sh errors none. .\" .sh notes .\" the glibc logmask handling was broken in versions before glibc 2.1.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br setlogmask () t} thread safety mt-unsafe race:logmask .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .\" note that the description in posix.1-2001 is flawed. .pp .br log_upto () will be included in the next release of the posix specification (issue 8). .\" fixme . https://www.austingroupbugs.net/view.php?id=1033 .sh see also .br closelog (3), .br openlog (3), .br syslog (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getgrnam.3 .\" copyright (c) 2007 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th euidaccess 3 2021-03-22 "" "linux programmer's manual" .sh name euidaccess, eaccess \- check effective user's permissions for a file .sh synopsis .nf .br "#define _gnu_source" " /* see feature_test_macros(7) */" .b #include .pp .bi "int euidaccess(const char *" pathname ", int " mode ); .bi "int eaccess(const char *" pathname ", int " mode ); .fi .sh description like .br access (2), .br euidaccess () checks permissions and existence of the file identified by its argument .ir pathname . however, whereas .br access (2) performs checks using the real user and group identifiers of the process, .br euidaccess () uses the effective identifiers. .pp .i mode is a mask consisting of one or more of .br r_ok ", " w_ok ", " x_ok ", and " f_ok , with the same meanings as for .br access (2). .pp .br eaccess () is a synonym for .br euidaccess (), provided for compatibility with some other systems. .sh return value on success (all requested permissions granted), zero is returned. on error (at least one bit in .i mode asked for a permission that is denied, or some other error occurred), \-1 is returned, and .i errno is set to indicate the error. .sh errors as for .br access (2). .sh versions the .br eaccess () function was added to glibc in version 2.4. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br euidaccess (), .br eaccess () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to these functions are nonstandard. some other systems have an .\" e.g., freebsd 6.1. .br eaccess () function. .sh notes .ir warning : using this function to check a process's permissions on a file before performing some operation based on that information leads to race conditions: the file permissions may change between the two steps. generally, it is safer just to attempt the desired operation and handle any permission error that occurs. .pp this function always dereferences symbolic links. if you need to check the permissions on a symbolic link, use .br faccessat (2) with the flags .br at_eaccess and .br at_symlink_nofollow . .sh see also .br access (2), .br chmod (2), .br chown (2), .br faccessat (2), .br open (2), .br setgid (2), .br setuid (2), .br stat (2), .br credentials (7), .br path_resolution (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/asin.3 .so man3/stailq.3 .so man2/swapon.2 .so man2/getresuid.2 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified 1993-07-24 by rik faith .\" modified 2004-10-10 by aeb .\" .th initgroups 3 2021-03-22 "gnu" "linux programmer's manual" .sh name initgroups \- initialize the supplementary group access list .sh synopsis .nf .b #include .b #include .pp .bi "int initgroups(const char *" user ", gid_t " group ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br initgroups (): .nf since glibc 2.19: _default_source glibc 2.19 and earlier: _bsd_source .fi .sh description the .br initgroups () function initializes the group access list by reading the group database .i /etc/group and using all groups of which .i user is a member. the additional group .i group is also added to the list. .pp the .i user argument must be non-null. .sh return value the .br initgroups () function returns 0 on success. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b enomem insufficient memory to allocate group information structure. .tp .b eperm the calling process has insufficient privilege. see the underlying system call .br setgroups (2). .sh files .tp .i /etc/group group database file .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br initgroups () t} thread safety mt-safe locale .te .hy .ad .sp 1 .sh conforming to svr4, 4.3bsd. .sh see also .br getgroups (2), .br setgroups (2), .br credentials (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1995 andries brouwer (aeb@cwi.nl) .\" written 10 june 1995 by andries brouwer .\" and copyright (c) 2007, 2015, 2020, michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified thu oct 31 15:16:23 1996 by eric s. raymond .\" .th llseek 2 2021-03-22 "linux" "linux programmer's manual" .sh name _llseek \- reposition read/write file offset .sh synopsis .nf .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "int syscall(sys__llseek, unsigned int " fd ", unsigned long " offset_high , .bi " unsigned long " offset_low ", loff_t *" result , .bi " unsigned int " whence ); .fi .pp .ir note : glibc provides no wrapper for .br _llseek (), necessitating the use of .br syscall (2). .sh description note: for information about the .br llseek (3) library function, see .br lseek64 (3). .pp the .br _llseek () system call repositions the offset of the open file description associated with the file descriptor .i fd to the value .ip (offset_high << 32) | offset_low .pp this new offset is a byte offset relative to the beginning of the file, the current file offset, or the end of the file, depending on whether .i whence is .br seek_set , .br seek_cur , or .br seek_end , respectively. .pp the new file offset is returned in the argument .ir result . the type .i loff_t is a 64-bit signed type. .pp this system call exists on various 32-bit platforms to support seeking to large file offsets. .sh return value upon successful completion, .br _llseek () returns 0. otherwise, a value of \-1 is returned and .i errno is set to indicate the error. .sh errors .tp .b ebadf .i fd is not an open file descriptor. .tp .b efault problem with copying results to user space. .tp .b einval .i whence is invalid. .sh conforming to this function is linux-specific, and should not be used in programs intended to be portable. .sh notes you probably want to use the .br lseek (2) wrapper function instead. .sh see also .br lseek (2), .br open (2), .br lseek64 (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getutent.3 .so man3/getline.3 .\" copyright (c) 2014 michael kerrisk .\" and copyright (c) 2014 peter zijlstra .\" and copyright (c) 2014 juri lelli .\" various pieces from the old sched_setscheduler(2) page .\" copyright (c) tom bjorkholm, markus kuhn & david a. wheeler 1996-1999 .\" and copyright (c) 2007 carsten emde .\" and copyright (c) 2008 michael kerrisk .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .\" worth looking at: http://rt.wiki.kernel.org/index.php .\" .th sched 7 2021-03-22 "linux" "linux programmer's manual" .sh name sched \- overview of cpu scheduling .sh description since linux 2.6.23, the default scheduler is cfs, the "completely fair scheduler". the cfs scheduler replaced the earlier "o(1)" scheduler. .\" .ss api summary linux provides the following system calls for controlling the cpu scheduling behavior, policy, and priority of processes (or, more precisely, threads). .tp .br nice (2) set a new nice value for the calling thread, and return the new nice value. .tp .br getpriority (2) return the nice value of a thread, a process group, or the set of threads owned by a specified user. .tp .br setpriority (2) set the nice value of a thread, a process group, or the set of threads owned by a specified user. .tp .br sched_setscheduler (2) set the scheduling policy and parameters of a specified thread. .tp .br sched_getscheduler (2) return the scheduling policy of a specified thread. .tp .br sched_setparam (2) set the scheduling parameters of a specified thread. .tp .br sched_getparam (2) fetch the scheduling parameters of a specified thread. .tp .br sched_get_priority_max (2) return the maximum priority available in a specified scheduling policy. .tp .br sched_get_priority_min (2) return the minimum priority available in a specified scheduling policy. .tp .br sched_rr_get_interval (2) fetch the quantum used for threads that are scheduled under the "round-robin" scheduling policy. .tp .br sched_yield (2) cause the caller to relinquish the cpu, so that some other thread be executed. .tp .br sched_setaffinity (2) (linux-specific) set the cpu affinity of a specified thread. .tp .br sched_getaffinity (2) (linux-specific) get the cpu affinity of a specified thread. .tp .br sched_setattr (2) set the scheduling policy and parameters of a specified thread. this (linux-specific) system call provides a superset of the functionality of .br sched_setscheduler (2) and .br sched_setparam (2). .tp .br sched_getattr (2) fetch the scheduling policy and parameters of a specified thread. this (linux-specific) system call provides a superset of the functionality of .br sched_getscheduler (2) and .br sched_getparam (2). .\" .ss scheduling policies the scheduler is the kernel component that decides which runnable thread will be executed by the cpu next. each thread has an associated scheduling policy and a \fistatic\fp scheduling priority, .ir sched_priority . the scheduler makes its decisions based on knowledge of the scheduling policy and static priority of all threads on the system. .pp for threads scheduled under one of the normal scheduling policies (\fbsched_other\fp, \fbsched_idle\fp, \fbsched_batch\fp), \fisched_priority\fp is not used in scheduling decisions (it must be specified as 0). .pp processes scheduled under one of the real-time policies (\fbsched_fifo\fp, \fbsched_rr\fp) have a \fisched_priority\fp value in the range 1 (low) to 99 (high). (as the numbers imply, real-time threads always have higher priority than normal threads.) note well: posix.1 requires an implementation to support only a minimum 32 distinct priority levels for the real-time policies, and some systems supply just this minimum. portable programs should use .br sched_get_priority_min (2) and .br sched_get_priority_max (2) to find the range of priorities supported for a particular policy. .pp conceptually, the scheduler maintains a list of runnable threads for each possible \fisched_priority\fp value. in order to determine which thread runs next, the scheduler looks for the nonempty list with the highest static priority and selects the thread at the head of this list. .pp a thread's scheduling policy determines where it will be inserted into the list of threads with equal static priority and how it will move inside this list. .pp all scheduling is preemptive: if a thread with a higher static priority becomes ready to run, the currently running thread will be preempted and returned to the wait list for its static priority level. the scheduling policy determines the ordering only within the list of runnable threads with equal static priority. .ss sched_fifo: first in-first out scheduling \fbsched_fifo\fp can be used only with static priorities higher than 0, which means that when a \fbsched_fifo\fp thread becomes runnable, it will always immediately preempt any currently running \fbsched_other\fp, \fbsched_batch\fp, or \fbsched_idle\fp thread. \fbsched_fifo\fp is a simple scheduling algorithm without time slicing. for threads scheduled under the \fbsched_fifo\fp policy, the following rules apply: .ip 1) 3 a running \fbsched_fifo\fp thread that has been preempted by another thread of higher priority will stay at the head of the list for its priority and will resume execution as soon as all threads of higher priority are blocked again. .ip 2) when a blocked \fbsched_fifo\fp thread becomes runnable, it will be inserted at the end of the list for its priority. .ip 3) if a call to .br sched_setscheduler (2), .br sched_setparam (2), .br sched_setattr (2), .br pthread_setschedparam (3), or .br pthread_setschedprio (3) changes the priority of the running or runnable .b sched_fifo thread identified by .i pid the effect on the thread's position in the list depends on the direction of the change to threads priority: .rs .ip \(bu 3 if the thread's priority is raised, it is placed at the end of the list for its new priority. as a consequence, it may preempt a currently running thread with the same priority. .ip \(bu if the thread's priority is unchanged, its position in the run list is unchanged. .ip \(bu if the thread's priority is lowered, it is placed at the front of the list for its new priority. .re .ip according to posix.1-2008, changes to a thread's priority (or policy) using any mechanism other than .br pthread_setschedprio (3) should result in the thread being placed at the end of the list for its priority. .\" in 2.2.x and 2.4.x, the thread is placed at the front of the queue .\" in 2.0.x, the right thing happened: the thread went to the back -- mtk .ip 4) a thread calling .br sched_yield (2) will be put at the end of the list. .pp no other events will move a thread scheduled under the \fbsched_fifo\fp policy in the wait list of runnable threads with equal static priority. .pp a \fbsched_fifo\fp thread runs until either it is blocked by an i/o request, it is preempted by a higher priority thread, or it calls .br sched_yield (2). .ss sched_rr: round-robin scheduling \fbsched_rr\fp is a simple enhancement of \fbsched_fifo\fp. everything described above for \fbsched_fifo\fp also applies to \fbsched_rr\fp, except that each thread is allowed to run only for a maximum time quantum. if a \fbsched_rr\fp thread has been running for a time period equal to or longer than the time quantum, it will be put at the end of the list for its priority. a \fbsched_rr\fp thread that has been preempted by a higher priority thread and subsequently resumes execution as a running thread will complete the unexpired portion of its round-robin time quantum. the length of the time quantum can be retrieved using .br sched_rr_get_interval (2). .\" on linux 2.4, the length of the rr interval is influenced .\" by the process nice value -- mtk .\" .ss sched_deadline: sporadic task model deadline scheduling since version 3.14, linux provides a deadline scheduling policy .rb ( sched_deadline ). this policy is currently implemented using gedf (global earliest deadline first) in conjunction with cbs (constant bandwidth server). to set and fetch this policy and associated attributes, one must use the linux-specific .br sched_setattr (2) and .br sched_getattr (2) system calls. .pp a sporadic task is one that has a sequence of jobs, where each job is activated at most once per period. each job also has a .ir "relative deadline" , before which it should finish execution, and a .ir "computation time" , which is the cpu time necessary for executing the job. the moment when a task wakes up because a new job has to be executed is called the .ir "arrival time" (also referred to as the request time or release time). the .ir "start time" is the time at which a task starts its execution. the .i "absolute deadline" is thus obtained by adding the relative deadline to the arrival time. .pp the following diagram clarifies these terms: .pp .in +4n .ex arrival/wakeup absolute deadline | start time | | | | v v v -----x--------xooooooooooooooooo--------x--------x--- |<- comp. time ->| |<------- relative deadline ------>| |<-------------- period ------------------->| .ee .in .pp when setting a .b sched_deadline policy for a thread using .br sched_setattr (2), one can specify three parameters: .ir runtime , .ir deadline , and .ir period . these parameters do not necessarily correspond to the aforementioned terms: usual practice is to set runtime to something bigger than the average computation time (or worst-case execution time for hard real-time tasks), deadline to the relative deadline, and period to the period of the task. thus, for .br sched_deadline scheduling, we have: .pp .in +4n .ex arrival/wakeup absolute deadline | start time | | | | v v v -----x--------xooooooooooooooooo--------x--------x--- |<-- runtime ------->| |<----------- deadline ----------->| |<-------------- period ------------------->| .ee .in .pp the three deadline-scheduling parameters correspond to the .ir sched_runtime , .ir sched_deadline , and .ir sched_period fields of the .i sched_attr structure; see .br sched_setattr (2). these fields express values in nanoseconds. .\" fixme it looks as though specifying sched_period as 0 means .\" "make sched_period the same as sched_deadline". .\" this needs to be documented. if .ir sched_period is specified as 0, then it is made the same as .ir sched_deadline . .pp the kernel requires that: .pp sched_runtime <= sched_deadline <= sched_period .pp .\" see __checkparam_dl in kernel/sched/core.c in addition, under the current implementation, all of the parameter values must be at least 1024 (i.e., just over one microsecond, which is the resolution of the implementation), and less than 2^63. if any of these checks fails, .br sched_setattr (2) fails with the error .br einval . .pp the cbs guarantees non-interference between tasks, by throttling threads that attempt to over-run their specified runtime. .pp to ensure deadline scheduling guarantees, the kernel must prevent situations where the set of .b sched_deadline threads is not feasible (schedulable) within the given constraints. the kernel thus performs an admittance test when setting or changing .b sched_deadline policy and attributes. this admission test calculates whether the change is feasible; if it is not, .br sched_setattr (2) fails with the error .br ebusy . .pp for example, it is required (but not necessarily sufficient) for the total utilization to be less than or equal to the total number of cpus available, where, since each thread can maximally run for runtime per period, that thread's utilization is its runtime divided by its period. .pp in order to fulfill the guarantees that are made when a thread is admitted to the .br sched_deadline policy, .br sched_deadline threads are the highest priority (user controllable) threads in the system; if any .br sched_deadline thread is runnable, it will preempt any thread scheduled under one of the other policies. .pp a call to .br fork (2) by a thread scheduled under the .b sched_deadline policy fails with the error .br eagain , unless the thread has its reset-on-fork flag set (see below). .pp a .b sched_deadline thread that calls .br sched_yield (2) will yield the current job and wait for a new period to begin. .\" .\" fixme calling sched_getparam() on a sched_deadline thread .\" fails with einval, but sched_getscheduler() succeeds. .\" is that intended? (why?) .\" .ss sched_other: default linux time-sharing scheduling \fbsched_other\fp can be used at only static priority 0 (i.e., threads under real-time policies always have priority over .b sched_other processes). \fbsched_other\fp is the standard linux time-sharing scheduler that is intended for all threads that do not require the special real-time mechanisms. .pp the thread to run is chosen from the static priority 0 list based on a \fidynamic\fp priority that is determined only inside this list. the dynamic priority is based on the nice value (see below) and is increased for each time quantum the thread is ready to run, but denied to run by the scheduler. this ensures fair progress among all \fbsched_other\fp threads. .pp in the linux kernel source code, the .b sched_other policy is actually named .br sched_normal . .\" .ss the nice value the nice value is an attribute that can be used to influence the cpu scheduler to favor or disfavor a process in scheduling decisions. it affects the scheduling of .br sched_other and .br sched_batch (see below) processes. the nice value can be modified using .br nice (2), .br setpriority (2), or .br sched_setattr (2). .pp according to posix.1, the nice value is a per-process attribute; that is, the threads in a process should share a nice value. however, on linux, the nice value is a per-thread attribute: different threads in the same process may have different nice values. .pp the range of the nice value varies across unix systems. on modern linux, the range is \-20 (high priority) to +19 (low priority). on some other systems, the range is \-20..20. very early linux kernels (before linux 2.0) had the range \-infinity..15. .\" linux before 1.3.36 had \-infinity..15. .\" since kernel 1.3.43, linux has the range \-20..19. .pp the degree to which the nice value affects the relative scheduling of .br sched_other processes likewise varies across unix systems and across linux kernel versions. .pp with the advent of the cfs scheduler in kernel 2.6.23, linux adopted an algorithm that causes relative differences in nice values to have a much stronger effect. in the current implementation, each unit of difference in the nice values of two processes results in a factor of 1.25 in the degree to which the scheduler favors the higher priority process. this causes very low nice values (+19) to truly provide little cpu to a process whenever there is any other higher priority load on the system, and makes high nice values (\-20) deliver most of the cpu to applications that require it (e.g., some audio applications). .pp on linux, the .br rlimit_nice resource limit can be used to define a limit to which an unprivileged process's nice value can be raised; see .br setrlimit (2) for details. .pp for further details on the nice value, see the subsections on the autogroup feature and group scheduling, below. .\" .ss sched_batch: scheduling batch processes (since linux 2.6.16.) \fbsched_batch\fp can be used only at static priority 0. this policy is similar to \fbsched_other\fp in that it schedules the thread according to its dynamic priority (based on the nice value). the difference is that this policy will cause the scheduler to always assume that the thread is cpu-intensive. consequently, the scheduler will apply a small scheduling penalty with respect to wakeup behavior, so that this thread is mildly disfavored in scheduling decisions. .pp .\" the following paragraph is drawn largely from the text that .\" accompanied ingo molnar's patch for the implementation of .\" sched_batch. .\" commit b0a9499c3dd50d333e2aedb7e894873c58da3785 this policy is useful for workloads that are noninteractive, but do not want to lower their nice value, and for workloads that want a deterministic scheduling policy without interactivity causing extra preemptions (between the workload's tasks). .\" .ss sched_idle: scheduling very low priority jobs (since linux 2.6.23.) \fbsched_idle\fp can be used only at static priority 0; the process nice value has no influence for this policy. .pp this policy is intended for running jobs at extremely low priority (lower even than a +19 nice value with the .b sched_other or .b sched_batch policies). .\" .ss resetting scheduling policy for child processes each thread has a reset-on-fork scheduling flag. when this flag is set, children created by .br fork (2) do not inherit privileged scheduling policies. the reset-on-fork flag can be set by either: .ip * 3 oring the .b sched_reset_on_fork flag into the .i policy argument when calling .br sched_setscheduler (2) (since linux 2.6.32); or .ip * specifying the .b sched_flag_reset_on_fork flag in .ir attr.sched_flags when calling .br sched_setattr (2). .pp note that the constants used with these two apis have different names. the state of the reset-on-fork flag can analogously be retrieved using .br sched_getscheduler (2) and .br sched_getattr (2). .pp the reset-on-fork feature is intended for media-playback applications, and can be used to prevent applications evading the .br rlimit_rttime resource limit (see .br getrlimit (2)) by creating multiple child processes. .pp more precisely, if the reset-on-fork flag is set, the following rules apply for subsequently created children: .ip * 3 if the calling thread has a scheduling policy of .b sched_fifo or .br sched_rr , the policy is reset to .br sched_other in child processes. .ip * if the calling process has a negative nice value, the nice value is reset to zero in child processes. .pp after the reset-on-fork flag has been enabled, it can be reset only if the thread has the .br cap_sys_nice capability. this flag is disabled in child processes created by .br fork (2). .\" .ss privileges and resource limits in linux kernels before 2.6.12, only privileged .rb ( cap_sys_nice ) threads can set a nonzero static priority (i.e., set a real-time scheduling policy). the only change that an unprivileged thread can make is to set the .b sched_other policy, and this can be done only if the effective user id of the caller matches the real or effective user id of the target thread (i.e., the thread specified by .ir pid ) whose policy is being changed. .pp a thread must be privileged .rb ( cap_sys_nice ) in order to set or modify a .br sched_deadline policy. .pp since linux 2.6.12, the .b rlimit_rtprio resource limit defines a ceiling on an unprivileged thread's static priority for the .b sched_rr and .b sched_fifo policies. the rules for changing scheduling policy and priority are as follows: .ip * 3 if an unprivileged thread has a nonzero .b rlimit_rtprio soft limit, then it can change its scheduling policy and priority, subject to the restriction that the priority cannot be set to a value higher than the maximum of its current priority and its .b rlimit_rtprio soft limit. .ip * if the .b rlimit_rtprio soft limit is 0, then the only permitted changes are to lower the priority, or to switch to a non-real-time policy. .ip * subject to the same rules, another unprivileged thread can also make these changes, as long as the effective user id of the thread making the change matches the real or effective user id of the target thread. .ip * special rules apply for the .br sched_idle policy. in linux kernels before 2.6.39, an unprivileged thread operating under this policy cannot change its policy, regardless of the value of its .br rlimit_rtprio resource limit. in linux kernels since 2.6.39, .\" commit c02aa73b1d18e43cfd79c2f193b225e84ca497c8 an unprivileged thread can switch to either the .br sched_batch or the .br sched_other policy so long as its nice value falls within the range permitted by its .br rlimit_nice resource limit (see .br getrlimit (2)). .pp privileged .rb ( cap_sys_nice ) threads ignore the .b rlimit_rtprio limit; as with older kernels, they can make arbitrary changes to scheduling policy and priority. see .br getrlimit (2) for further information on .br rlimit_rtprio . .ss limiting the cpu usage of real-time and deadline processes a nonblocking infinite loop in a thread scheduled under the .br sched_fifo , .br sched_rr , or .br sched_deadline policy can potentially block all other threads from accessing the cpu forever. prior to linux 2.6.25, the only way of preventing a runaway real-time process from freezing the system was to run (at the console) a shell scheduled under a higher static priority than the tested application. this allows an emergency kill of tested real-time applications that do not block or terminate as expected. .pp since linux 2.6.25, there are other techniques for dealing with runaway real-time and deadline processes. one of these is to use the .br rlimit_rttime resource limit to set a ceiling on the cpu time that a real-time process may consume. see .br getrlimit (2) for details. .pp since version 2.6.25, linux also provides two .i /proc files that can be used to reserve a certain amount of cpu time to be used by non-real-time processes. reserving cpu time in this fashion allows some cpu time to be allocated to (say) a root shell that can be used to kill a runaway process. both of these files specify time values in microseconds: .tp .ir /proc/sys/kernel/sched_rt_period_us this file specifies a scheduling period that is equivalent to 100% cpu bandwidth. the value in this file can range from 1 to .br int_max , giving an operating range of 1 microsecond to around 35 minutes. the default value in this file is 1,000,000 (1 second). .tp .ir /proc/sys/kernel/sched_rt_runtime_us the value in this file specifies how much of the "period" time can be used by all real-time and deadline scheduled processes on the system. the value in this file can range from \-1 to .br int_max \-1. specifying \-1 makes the run time the same as the period; that is, no cpu time is set aside for non-real-time processes (which was the linux behavior before kernel 2.6.25). the default value in this file is 950,000 (0.95 seconds), meaning that 5% of the cpu time is reserved for processes that don't run under a real-time or deadline scheduling policy. .ss response time a blocked high priority thread waiting for i/o has a certain response time before it is scheduled again. the device driver writer can greatly reduce this response time by using a "slow interrupt" interrupt handler. .\" as described in .\" .br request_irq (9). .ss miscellaneous child processes inherit the scheduling policy and parameters across a .br fork (2). the scheduling policy and parameters are preserved across .br execve (2). .pp memory locking is usually needed for real-time processes to avoid paging delays; this can be done with .br mlock (2) or .br mlockall (2). .\" .ss the autogroup feature .\" commit 5091faa449ee0b7d73bc296a93bca9540fc51d0a since linux 2.6.38, the kernel provides a feature known as autogrouping to improve interactive desktop performance in the face of multiprocess, cpu-intensive workloads such as building the linux kernel with large numbers of parallel build processes (i.e., the .br make (1) .br \-j flag). .pp this feature operates in conjunction with the cfs scheduler and requires a kernel that is configured with .br config_sched_autogroup . on a running system, this feature is enabled or disabled via the file .ir /proc/sys/kernel/sched_autogroup_enabled ; a value of 0 disables the feature, while a value of 1 enables it. the default value in this file is 1, unless the kernel was booted with the .ir noautogroup parameter. .pp a new autogroup is created when a new session is created via .br setsid (2); this happens, for example, when a new terminal window is started. a new process created by .br fork (2) inherits its parent's autogroup membership. thus, all of the processes in a session are members of the same autogroup. an autogroup is automatically destroyed when the last process in the group terminates. .pp when autogrouping is enabled, all of the members of an autogroup are placed in the same kernel scheduler "task group". the cfs scheduler employs an algorithm that equalizes the distribution of cpu cycles across task groups. the benefits of this for interactive desktop performance can be described via the following example. .pp suppose that there are two autogroups competing for the same cpu (i.e., presume either a single cpu system or the use of .br taskset (1) to confine all the processes to the same cpu on an smp system). the first group contains ten cpu-bound processes from a kernel build started with .ir "make\ \-j10" . the other contains a single cpu-bound process: a video player. the effect of autogrouping is that the two groups will each receive half of the cpu cycles. that is, the video player will receive 50% of the cpu cycles, rather than just 9% of the cycles, which would likely lead to degraded video playback. the situation on an smp system is more complex, .\" mike galbraith, 25 nov 2016: .\" i'd say something more wishy-washy here, like cycles are .\" distributed fairly across groups and leave it at that, as your .\" detailed example is incorrect due to smp fairness (which i don't .\" like much because [very unlikely] worst case scenario .\" renders a box sized group incapable of utilizing more that .\" a single cpu total). for example, if a group of nr_cpus .\" size competes with a singleton, load balancing will try to give .\" the singleton a full cpu of its very own. if groups intersect for .\" whatever reason on say my quad lappy, distribution is 80/20 in .\" favor of the singleton. but the general effect is the same: the scheduler distributes cpu cycles across task groups such that an autogroup that contains a large number of cpu-bound processes does not end up hogging cpu cycles at the expense of the other jobs on the system. .pp a process's autogroup (task group) membership can be viewed via the file .ir /proc/[pid]/autogroup : .pp .in +4n .ex $ \fbcat /proc/1/autogroup\fp /autogroup\-1 nice 0 .ee .in .pp this file can also be used to modify the cpu bandwidth allocated to an autogroup. this is done by writing a number in the "nice" range to the file to set the autogroup's nice value. the allowed range is from +19 (low priority) to \-20 (high priority). (writing values outside of this range causes .br write (2) to fail with the error .br einval .) .\" fixme . .\" because of a bug introduced in linux 4.7 .\" (commit 2159197d66770ec01f75c93fb11dc66df81fd45b made changes .\" that exposed the fact that autogroup didn't call scale_load()), .\" it happened that *all* values in this range caused a task group .\" to be further disfavored by the scheduler, with \-20 resulting .\" in the scheduler mildly disfavoring the task group and +19 greatly .\" disfavoring it. .\" .\" a patch was posted on 23 nov 2016 .\" ("sched/autogroup: fix 64bit kernel nice adjustment"; .\" check later to see in which kernel version it lands. .pp the autogroup nice setting has the same meaning as the process nice value, but applies to distribution of cpu cycles to the autogroup as a whole, based on the relative nice values of other autogroups. for a process inside an autogroup, the cpu cycles that it receives will be a product of the autogroup's nice value (compared to other autogroups) and the process's nice value (compared to other processes in the same autogroup. .pp the use of the .br cgroups (7) cpu controller to place processes in cgroups other than the root cpu cgroup overrides the effect of autogrouping. .pp the autogroup feature groups only processes scheduled under non-real-time policies .rb ( sched_other , .br sched_batch , and .br sched_idle ). it does not group processes scheduled under real-time and deadline policies. those processes are scheduled according to the rules described earlier. .\" .ss the nice value and group scheduling when scheduling non-real-time processes (i.e., those scheduled under the .br sched_other , .br sched_batch , and .br sched_idle policies), the cfs scheduler employs a technique known as "group scheduling", if the kernel was configured with the .br config_fair_group_sched option (which is typical). .pp under group scheduling, threads are scheduled in "task groups". task groups have a hierarchical relationship, rooted under the initial task group on the system, known as the "root task group". task groups are formed in the following circumstances: .ip * 3 all of the threads in a cpu cgroup form a task group. the parent of this task group is the task group of the corresponding parent cgroup. .ip * if autogrouping is enabled, then all of the threads that are (implicitly) placed in an autogroup (i.e., the same session, as created by .br setsid (2)) form a task group. each new autogroup is thus a separate task group. the root task group is the parent of all such autogroups. .ip * if autogrouping is enabled, then the root task group consists of all processes in the root cpu cgroup that were not otherwise implicitly placed into a new autogroup. .ip * if autogrouping is disabled, then the root task group consists of all processes in the root cpu cgroup. .ip * if group scheduling was disabled (i.e., the kernel was configured without .br config_fair_group_sched ), then all of the processes on the system are notionally placed in a single task group. .pp under group scheduling, a thread's nice value has an effect for scheduling decisions .ir "only relative to other threads in the same task group" . this has some surprising consequences in terms of the traditional semantics of the nice value on unix systems. in particular, if autogrouping is enabled (which is the default in various distributions), then employing .br setpriority (2) or .br nice (1) on a process has an effect only for scheduling relative to other processes executed in the same session (typically: the same terminal window). .pp conversely, for two processes that are (for example) the sole cpu-bound processes in different sessions (e.g., different terminal windows, each of whose jobs are tied to different autogroups), .ir "modifying the nice value of the process in one of the sessions" .ir "has no effect" in terms of the scheduler's decisions relative to the process in the other session. .\" more succinctly: the nice(1) command is in many cases a no-op since .\" linux 2.6.38. .\" a possibly useful workaround here is to use a command such as the following to modify the autogroup nice value for .i all of the processes in a terminal session: .pp .in +4n .ex $ \fbecho 10 > /proc/self/autogroup\fp .ee .in .ss real-time features in the mainline linux kernel .\" fixme . probably this text will need some minor tweaking .\" ask carsten emde about this. since kernel version 2.6.18, linux is gradually becoming equipped with real-time capabilities, most of which are derived from the former .i realtime\-preempt patch set. until the patches have been completely merged into the mainline kernel, they must be installed to achieve the best real-time performance. these patches are named: .pp .in +4n .ex patch\-\fikernelversion\fp\-rt\fipatchversion\fp .ee .in .pp and can be downloaded from .ur http://www.kernel.org\:/pub\:/linux\:/kernel\:/projects\:/rt/ .ue . .pp without the patches and prior to their full inclusion into the mainline kernel, the kernel configuration offers only the three preemption classes .br config_preempt_none , .br config_preempt_voluntary , and .b config_preempt_desktop which respectively provide no, some, and considerable reduction of the worst-case scheduling latency. .pp with the patches applied or after their full inclusion into the mainline kernel, the additional configuration item .b config_preempt_rt becomes available. if this is selected, linux is transformed into a regular real-time operating system. the fifo and rr scheduling policies are then used to run a thread with true real-time priority and a minimum worst-case scheduling latency. .sh notes the .br cgroups (7) cpu controller can be used to limit the cpu consumption of groups of processes. .pp originally, standard linux was intended as a general-purpose operating system being able to handle background processes, interactive applications, and less demanding real-time applications (applications that need to usually meet timing deadlines). although the linux kernel 2.6 allowed for kernel preemption and the newly introduced o(1) scheduler ensures that the time needed to schedule is fixed and deterministic irrespective of the number of active tasks, true real-time computing was not possible up to kernel version 2.6.17. .sh see also .ad l .nh .br chcpu (1), .br chrt (1), .br lscpu (1), .br ps (1), .br taskset (1), .br top (1), .br getpriority (2), .br mlock (2), .br mlockall (2), .br munlock (2), .br munlockall (2), .br nice (2), .br sched_get_priority_max (2), .br sched_get_priority_min (2), .br sched_getaffinity (2), .br sched_getparam (2), .br sched_getscheduler (2), .br sched_rr_get_interval (2), .br sched_setaffinity (2), .br sched_setparam (2), .br sched_setscheduler (2), .br sched_yield (2), .br setpriority (2), .br pthread_getaffinity_np (3), .br pthread_getschedparam (3), .br pthread_setaffinity_np (3), .br sched_getcpu (3), .br capabilities (7), .br cpuset (7) .ad .pp .i programming for the real world \- posix.4 by bill o.\& gallmeister, o'reilly & associates, inc., isbn 1-56592-074-0. .pp the linux kernel source files .ir documentation/scheduler/sched\-deadline.txt , .ir documentation/scheduler/sched\-rt\-group.txt , .ir documentation/scheduler/sched\-design\-cfs.txt , and .ir documentation/scheduler/sched\-nice\-design.txt .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/floor.3 .so man3/ctime.3 .so man3/error.3 .\" copyright 1995 jim van zandt .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" changed `square root' into `cube root' - aeb, 950919 .\" .\" modified 2002-07-27 walter harms .\" (walter.harms@informatik.uni-oldenburg.de) .\" .th cbrt 3 2021-03-22 "gnu" "linux programmer's manual" .sh name cbrt, cbrtf, cbrtl \- cube root function .sh synopsis .nf .b #include .pp .bi "double cbrt(double " x ); .bi "float cbrtf(float " x ); .bi "long double cbrtl(long double " x ); .fi .pp link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br cbrt (): .nf _isoc99_source || _posix_c_source >= 200112l || _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .pp .br cbrtf (), .br cbrtl (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description these functions return the (real) cube root of .ir x . this function cannot fail; every representable real value has a representable real cube root. .sh return value these functions return the cube root of .ir x . .pp if .i x is +0, \-0, positive infinity, negative infinity, or nan, .i x is returned. .sh errors no errors occur. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br cbrt (), .br cbrtf (), .br cbrtl () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to c99, posix.1-2001, posix.1-2008. .\" .br cbrt () .\" was a gnu extension. it is now a c99 requirement. .sh see also .br pow (3), .br sqrt (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getopt.3 .so man3/xdr.3 .so man3/drand48_r.3 .so man3/fpclassify.3 .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification .\" http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .\" modified tue oct 16 23:18:40 bst 2001 by john levon .th fgetws 3 2021-03-22 "gnu" "linux programmer's manual" .sh name fgetws \- read a wide-character string from a file stream .sh synopsis .nf .b #include .pp .bi "wchar_t *fgetws(wchar_t *restrict " ws ", int " n \ ", file *restrict " stream ); .fi .sh description the .br fgetws () function is the wide-character equivalent of the .br fgets (3) function. it reads a string of at most \fin\-1\fp wide characters into the wide-character array pointed to by \fiws\fp, and adds a terminating null wide character (l\(aq\e0\(aq). it stops reading wide characters after it has encountered and stored a newline wide character. it also stops when end of stream is reached. .pp the programmer must ensure that there is room for at least \fin\fp wide characters at \fiws\fp. .pp for a nonlocking counterpart, see .br unlocked_stdio (3). .sh return value the .br fgetws () function, if successful, returns \fiws\fp. if end of stream was already reached or if an error occurred, it returns null. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br fgetws () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh notes the behavior of .br fgetws () depends on the .b lc_ctype category of the current locale. .pp in the absence of additional information passed to the .br fopen (3) call, it is reasonable to expect that .br fgetws () will actually read a multibyte string from the stream and then convert it to a wide-character string. .pp this function is unreliable, because it does not permit to deal properly with null wide characters that may be present in the input. .sh see also .br fgetwc (3), .br unlocked_stdio (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/gethostname.2 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sat jul 24 17:48:42 1993 by rik faith (faith@cs.unc.edu) .th telldir 3 2021-03-22 "" "linux programmer's manual" .sh name telldir \- return current location in directory stream .sh synopsis .nf .b #include .pp .bi "long telldir(dir *" dirp ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br telldir (): .nf _xopen_source || /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description the .br telldir () function returns the current location associated with the directory stream \fidirp\fp. .sh return value on success, the .br telldir () function returns the current location in the directory stream. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b ebadf invalid directory stream descriptor \fidirp\fp. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br telldir () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, 4.3bsd. .sh notes in glibc up to version 2.1.1, the return type of .br telldir () was .ir off_t . posix.1-2001 specifies .ir long , and this is the type used since glibc 2.1.2. .pp in early filesystems, the value returned by .br telldir () was a simple file offset within a directory. modern filesystems use tree or hash structures, rather than flat tables, to represent directories. on such filesystems, the value returned by .br telldir () (and used internally by .br readdir (3)) is a "cookie" that is used by the implementation to derive a position within a directory. .\" https://lwn.net/articles/544298/ application programs should treat this strictly as an opaque value, making .i no assumptions about its contents. .sh see also .br closedir (3), .br opendir (3), .br readdir (3), .br rewinddir (3), .br scandir (3), .br seekdir (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/gamma.3 .so man3/cimag.3 .\" copyright (c) 2007 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" 2007-10-23 mtk, nearly a complete rewrite of the earlier page. .th intro 3 2020-11-01 "linux" "linux programmer's manual" .sh name intro \- introduction to library functions .sh description section 3 of the manual describes all library functions excluding the library functions (system call wrappers) described in section 2, which implement system calls. .pp many of the functions described in the section are part of the standard c library .ri ( libc ). some functions are part of other libraries (e.g., the math library, .ir libm , or the real-time library, .ir librt ) in which case the manual page will indicate the linker option needed to link against the required library (e.g., .i \-lm and .ir \-lrt , respectively, for the aforementioned libraries). .pp in some cases, the programmer must define a feature test macro in order to obtain the declaration of a function from the header file specified in the man page synopsis section. (where required, these feature test macros must be defined before including .i any header files.) in such cases, the required macro is described in the man page. for further information on feature test macros, see .br feature_test_macros (7). .\" .\" there .\" are various function groups which can be identified by a letter which .\" is appended to the chapter number: .\" .ip (3c) .\" these functions, the functions from chapter 2 and from chapter 3s are .\" contained in the c standard library libc, which will be used by .\" .br cc (1) .\" by default. .\" .ip (3s) .\" these functions are parts of the .\" .br stdio (3) .\" library. they are contained in the standard c library libc. .\" .ip (3m) .\" these functions are contained in the arithmetic library libm. they are .\" used by the .\" .br f77 (1) .\" fortran compiler by default, but not by the .\" .br cc (1) .\" c compiler, which needs the option \fi\-lm\fp. .\" .ip (3f) .\" these functions are part of the fortran library libf77. there are no .\" special compiler flags needed to use these functions. .\" .ip (3x) .\" various special libraries. the manual pages documenting their functions .\" specify the library names. .sh conforming to certain terms and abbreviations are used to indicate unix variants and standards to which calls in this section conform. see .br standards (7). .sh notes .ss authors and copyright conditions look at the header of the manual page source for the author(s) and copyright conditions. note that these can be different from page to page! .sh see also .br intro (2), .br errno (3), .br capabilities (7), .br credentials (7), .br environ (7), .br feature_test_macros (7), .br libc (7), .br math_error (7), .br path_resolution (7), .br pthreads (7), .br signal (7), .br standards (7), .br system_data_types (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/dladdr.3 .so man3/casinh.3 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" and copyright 2008, linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified 1993-07-24 by rik faith (faith@cs.unc.edu) .\" modified 2002-07-27 by walter harms .\" (walter.harms@informatik.uni-oldenburg.de) .\" .th tan 3 2021-03-22 "" "linux programmer's manual" .sh name tan, tanf, tanl \- tangent function .sh synopsis .nf .b #include .pp .bi "double tan(double " x ); .bi "float tanf(float " x ); .bi "long double tanl(long double " x ); .fi .pp link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br tanf (), .br tanl (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description these functions return the tangent of .ir x , where .i x is given in radians. .sh return value on success, these functions return the tangent of .ir x . .pp if .i x is a nan, a nan is returned. .pp if .i x is positive infinity or negative infinity, a domain error occurs, and a nan is returned. .pp if the correct result would overflow, a range error occurs, and the functions return .br huge_val , .br huge_valf , or .br huge_vall , respectively, with the mathematically correct sign. .\" i think overflow can't occur, because the closest floating-point .\" representation of pi/2 is still not close enough to pi/2 to .\" produce a large enough value to overflow. .\" testing certainly seems to bear this out. -- mtk, jul 08 .\" .\" posix.1 allows an optional underflow error; .\" glibc 2.8 doesn't do this .\" posix.1 an optional range error for subnormal x; .\" glibc 2.8 doesn't do this .sh errors see .br math_error (7) for information on how to determine whether an error has occurred when calling these functions. .pp the following errors can occur: .tp domain error: \fix\fp is an infinity .i errno is set to .b edom (but see bugs). an invalid floating-point exception .rb ( fe_invalid ) is raised. .tp range error: result overflow .\" unable to test this case, since the best approximation of .\" pi/2 in double precision only yields a tan() value of 1.633e16. .\" .i errno .\" is set to .\" .br erange . an overflow floating-point exception .rb ( fe_overflow ) is raised. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br tan (), .br tanf (), .br tanl () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to c99, posix.1-2001, posix.1-2008. .pp the variant returning .i double also conforms to svr4, 4.3bsd, c89. .sh bugs before version 2.10, the glibc implementation did not set .\" http://sourceware.org/bugzilla/show_bug.cgi?id=6782 .i errno to .b edom when a domain error occurred. .sh see also .br acos (3), .br asin (3), .br atan (3), .br atan2 (3), .br cos (3), .br ctan (3), .br sin (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/rpc.3 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sat jul 24 18:49:23 1993 by rik faith (faith@cs.unc.edu) .th memset 3 2021-03-22 "gnu" "linux programmer's manual" .sh name memset \- fill memory with a constant byte .sh synopsis .nf .b #include .pp .bi "void *memset(void *" s ", int " c ", size_t " n ); .fi .sh description the .br memset () function fills the first .i n bytes of the memory area pointed to by .i s with the constant byte .ir c . .sh return value the .br memset () function returns a pointer to the memory area .ir s . .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br memset () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c89, c99, svr4, 4.3bsd. .sh see also .br bstring (3), .br bzero (3), .br swab (3), .br wmemset (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 2003 walter harms (walter.harms@informatik.uni-oldenburg.de) .\" .\" %%%license_start(gpl_noversion_oneline) .\" distributed under gpl .\" %%%license_end .\" .\" this is the 3rd type of interface for cryptographic routines .\" 1. encrypt() expects a bit field .\" 2. cbc_crypt() byte values .\" 3. xencrypt() a hexstring .\" to bad to be true :( .\" .th xcrypt 3 2021-03-22 "" "linux programmer's manual" .sh name xencrypt, xdecrypt, passwd2des \- rfs password encryption .sh synopsis .nf .b "#include " .pp .bi "void passwd2des(char " *passwd ", char *" key ");" .pp .bi "int xencrypt(char *" secret ", char *" passwd ");" .bi "int xdecrypt(char *" secret ", char *" passwd ");" .fi .sh description .br warning : do not use these functions in new code. they do not achieve any type of acceptable cryptographic security guarantees. .pp the function .br passwd2des () takes a character string .i passwd of arbitrary length and fills a character array .i key of length 8. the array .i key is suitable for use as des key. it has odd parity set in bit 0 of each byte. both other functions described here use this function to turn their argument .i passwd into a des key. .pp the .br xencrypt () function takes the ascii character string .i secret given in hex, .\" (over the alphabet 0123456789abcdefabcdef), which must have a length that is a multiple of 16, encrypts it using the des key derived from .i passwd by .br passwd2des (), and outputs the result again in .i secret as a hex string .\" (over the alphabet 0123456789abcdef) of the same length. .pp the .br xdecrypt () function performs the converse operation. .sh return value the functions .br xencrypt () and .br xdecrypt () return 1 on success and 0 on error. .sh versions these functions are available in glibc since version 2.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br passwd2des (), .br xencrypt (), .br xdecrypt () t} thread safety mt-safe .te .hy .ad .sp 1 .sh bugs the prototypes are missing from the abovementioned include file. .sh see also .br cbc_crypt (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/termios.3 .\" copyright (c) 2017 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_atfork 3 2020-08-13 "linux" "linux programmer's manual" .sh name pthread_atfork \- register fork handlers .sh synopsis .nf .b #include .pp .bi "int pthread_atfork(void (*" prepare ")(void), void (*" parent ")(void)," .bi " void (*" child ")(void));" .fi .pp link with \fi\-pthread\fp. .sh description the .br pthread_atfork () function registers fork handlers that are to be executed when .br fork (2) is called by this thread. the handlers are executed in the context of the thread that calls .br fork (2). .pp three kinds of handler can be registered: .ip * 3 .ir prepare specifies a handler that is executed before .br fork (2) processing starts. .ip * .i parent specifies a handler that is executed in the parent process after .br fork (2) processing completes. .ip * .i child specifies a handler that is executed in the child process after .br fork (2) processing completes. .pp any of the three arguments may be null if no handler is needed in the corresponding phase of .br fork (2) processing. .sh return value on success, .br pthread_atfork () returns zero. on error, it returns an error number. .br pthread_atfork () may be called multiple times by a thread, to register multiple handlers for each phase. the handlers for each phase are called in a specified order: the .i prepare handlers are called in reverse order of registration; the .i parent and .i child handlers are called in the order of registration. .sh errors .tp .b enomem could not allocate memory to record the form handler entry. .sh conforming to posix.1-2001, posix.1-2008. .sh notes when .br fork (2) is called in a multithreaded process, only the calling thread is duplicated in the child process. the original intention of .br pthread_atfork () was to allow the calling thread to be returned to a consistent state. for example, at the time of the call to .br fork (2), other threads may have locked mutexes that are visible in the user-space memory duplicated in the child. such mutexes would never be unlocked, since the threads that placed the locks are not duplicated in the child. the intent of .br pthread_atfork () was to provide a mechanism whereby the application (or a library) could ensure that mutexes and other process and thread state would be restored to a consistent state. in practice, this task is generally too difficult to be practicable. .pp after a .br fork (2) in a multithreaded process returns in the child, the child should call only async-signal-safe functions (see .br signal\-safety (7)) until such time as it calls .br execve (2) to execute a new program. .pp posix.1 specifies that .br pthread_atfork () shall not fail with the error .br eintr . .sh see also .br fork (2), .br atexit (3), .br pthreads (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getutent.3 .so man3/unlocked_stdio.3 .\" copyright 1995 james r. van zandt .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th stpcpy 3 2021-03-22 "gnu" "linux programmer's manual" .sh name stpcpy \- copy a string returning a pointer to its end .sh synopsis .nf .b #include .pp .bi "char *stpcpy(char *restrict " dest ", const char *restrict " src ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br stpcpy (): .nf since glibc 2.10: _posix_c_source >= 200809l before glibc 2.10: _gnu_source .fi .sh description the .br stpcpy () function copies the string pointed to by .i src (including the terminating null byte (\(aq\e0\(aq)) to the array pointed to by .ir dest . the strings may not overlap, and the destination string .i dest must be large enough to receive the copy. .sh return value .br stpcpy () returns a pointer to the .b end of the string .i dest (that is, the address of the terminating null byte) rather than the beginning. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br stpcpy () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to this function was added to posix.1-2008. before that, it was not part of the c or posix.1 standards, nor customary on unix systems. it first appeared at least as early as 1986, in the lattice c amigados compiler, then in the gnu fileutils and gnu textutils in 1989, and in the gnu c library by 1992. it is also present on the bsds. .sh bugs this function may overrun the buffer .ir dest . .sh examples for example, this program uses .br stpcpy () to concatenate .b foo and .b bar to produce .br foobar , which it then prints. .pp .ex #define _gnu_source #include #include int main(void) { char buffer[20]; char *to = buffer; to = stpcpy(to, "foo"); to = stpcpy(to, "bar"); printf("%s\en", buffer); } .ee .sh see also .br bcopy (3), .br memccpy (3), .br memcpy (3), .br memmove (3), .br stpncpy (3), .br strcpy (3), .br string (3), .br wcpcpy (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/lround.3 .so man3/getnetent.3 .so man2/accept.2 .so man3/cpow.3 .\" copyright (c) 2019 aleksa sarai .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .th openat2 2 2021-03-22 "linux" "linux programmer's manual" .sh name openat2 \- open and possibly create a file (extended) .sh synopsis .nf .br "#include " \ " /* definition of " o_* " and " s_* " constants */" .br "#include " " /* definition of " resolve_* " constants */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "long syscall(sys_openat2, int " dirfd ", const char *" pathname , .bi " struct open_how *" how ", size_t " size ); .fi .pp .ir note : glibc provides no wrapper for .br openat2 (), necessitating the use of .br syscall (2). .sh description the .br openat2 () system call is an extension of .br openat (2) and provides a superset of its functionality. .pp the .br openat2 () system call opens the file specified by .ir pathname . if the specified file does not exist, it may optionally (if .b o_creat is specified in .ir how.flags ) be created. .pp as with .br openat (2), if .i pathname is a relative pathname, then it is interpreted relative to the directory referred to by the file descriptor .i dirfd (or the current working directory of the calling process, if .i dirfd is the special value .br at_fdcwd ). if .i pathname is an absolute pathname, then .i dirfd is ignored (unless .i how.resolve contains .br resolve_in_root , in which case .i pathname is resolved relative to .ir dirfd ). .pp rather than taking a single .i flags argument, an extensible structure (\fihow\fp) is passed to allow for future extensions. the .i size argument must be specified as .ir "sizeof(struct open_how)" . .\" .ss the open_how structure the .i how argument specifies how .i pathname should be opened, and acts as a superset of the .ir flags and .ir mode arguments to .br openat (2). this argument is a pointer to a structure of the following form: .pp .in +4n .ex struct open_how { u64 flags; /* o_* flags */ u64 mode; /* mode for o_{creat,tmpfile} */ u64 resolve; /* resolve_* flags */ /* ... */ }; .ee .in .pp any future extensions to .br openat2 () will be implemented as new fields appended to the above structure, with a zero value in a new field resulting in the kernel behaving as though that extension field was not present. therefore, the caller .i must zero-fill this structure on initialization. (see the "extensibility" section of the .b notes for more detail on why this is necessary.) .pp the fields of the .i open_how structure are as follows: .tp .i flags this field specifies the file creation and file status flags to use when opening the file. all of the .b o_* flags defined for .br openat (2) are valid .br openat2 () flag values. .ip whereas .br openat (2) ignores unknown bits in its .i flags argument, .br openat2 () returns an error if unknown or conflicting flags are specified in .ir how.flags . .tp .i mode this field specifies the mode for the new file, with identical semantics to the .i mode argument of .br openat (2). .ip whereas .br openat (2) ignores bits other than those in the range .i 07777 in its .i mode argument, .br openat2 () returns an error if .i how.mode contains bits other than .ir 07777 . similarly, an error is returned if .br openat2 () is called with a nonzero .ir how.mode and .ir how.flags does not contain .br o_creat or .br o_tmpfile . .tp .i resolve this is a bit-mask of flags that modify the way in which .b all components of .i pathname will be resolved. (see .br path_resolution (7) for background information.) .ip the primary use case for these flags is to allow trusted programs to restrict how untrusted paths (or paths inside untrusted directories) are resolved. the full list of .i resolve flags is as follows: .rs .tp .b resolve_beneath .\" commit adb21d2b526f7f196b2f3fdca97d80ba05dd14a0 do not permit the path resolution to succeed if any component of the resolution is not a descendant of the directory indicated by .ir dirfd . this causes absolute symbolic links (and absolute values of .ir pathname ) to be rejected. .ip currently, this flag also disables magic-link resolution (see below). however, this may change in the future. therefore, to ensure that magic links are not resolved, the caller should explicitly specify .br resolve_no_magiclinks . .tp .b resolve_in_root .\" commit 8db52c7e7ee1bd861b6096fcafc0fe7d0f24a994 treat the directory referred to by .i dirfd as the root directory while resolving .ir pathname . absolute symbolic links are interpreted relative to .ir dirfd . if a prefix component of .i pathname equates to .ir dirfd , then an immediately following .ir ..\& component likewise equates to .ir dirfd (just as .i /..\& is traditionally equivalent to .ir / ). if .i pathname is an absolute path, it is also interpreted relative to .ir dirfd . .ip the effect of this flag is as though the calling process had used .br chroot (2) to (temporarily) modify its root directory (to the directory referred to by .ir dirfd ). however, unlike .br chroot (2) (which changes the filesystem root permanently for a process), .b resolve_in_root allows a program to efficiently restrict path resolution on a per-open basis. .ip currently, this flag also disables magic-link resolution. however, this may change in the future. therefore, to ensure that magic links are not resolved, the caller should explicitly specify .br resolve_no_magiclinks . .tp .b resolve_no_magiclinks .\" commit 278121417a72d87fb29dd8c48801f80821e8f75a disallow all magic-link resolution during path resolution. .ip magic links are symbolic link-like objects that are most notably found in .br proc (5); examples include .ir /proc/[pid]/exe and .ir /proc/[pid]/fd/* . (see .br symlink (7) for more details.) .ip unknowingly opening magic links can be risky for some applications. examples of such risks include the following: .rs .ip \(bu 2 if the process opening a pathname is a controlling process that currently has no controlling terminal (see .br credentials (7)), then opening a magic link inside .ir /proc/[pid]/fd that happens to refer to a terminal would cause the process to acquire a controlling terminal. .ip \(bu .\" from https://lwn.net/articles/796868/: .\" the presence of this flag will prevent a path lookup operation .\" from traversing through one of these magic links, thus blocking .\" (for example) attempts to escape from a container via a /proc .\" entry for an open file descriptor. in a containerized environment, a magic link inside .i /proc may refer to an object outside the container, and thus may provide a means to escape from the container. .re .ip because of such risks, an application may prefer to disable magic link resolution using the .br resolve_no_magiclinks flag. .ip if the trailing component (i.e., basename) of .i pathname is a magic link, .i how.resolve contains .br resolve_no_magiclinks , and .i how.flags contains both .br o_path and .br o_nofollow , then an .b o_path file descriptor referencing the magic link will be returned. .tp .b resolve_no_symlinks .\" commit 278121417a72d87fb29dd8c48801f80821e8f75a disallow resolution of symbolic links during path resolution. this option implies .br resolve_no_magiclinks . .ip if the trailing component (i.e., basename) of .i pathname is a symbolic link, .i how.resolve contains .br resolve_no_symlinks , and .i how.flags contains both .br o_path and .br o_nofollow , then an .b o_path file descriptor referencing the symbolic link will be returned. .ip note that the effect of the .br resolve_no_symlinks flag, which affects the treatment of symbolic links in all of the components of .ir pathname , differs from the effect of the .br o_nofollow file creation flag (in .ir how.flags ), which affects the handling of symbolic links only in the final component of .ir pathname . .ip applications that employ the .br resolve_no_symlinks flag are encouraged to make its use configurable (unless it is used for a specific security purpose), as symbolic links are very widely used by end-users. setting this flag indiscriminately\(emi.e., for purposes not specifically related to security\(emfor all uses of .br openat2 () may result in spurious errors on previously functional systems. this may occur if, for example, a system pathname that is used by an application is modified (e.g., in a new distribution release) so that a pathname component (now) contains a symbolic link. .tp .b resolve_no_xdev .\" commit 72ba29297e1439efaa54d9125b866ae9d15df339 disallow traversal of mount points during path resolution (including all bind mounts). consequently, .i pathname must either be on the same mount as the directory referred to by .ir dirfd , or on the same mount as the current working directory if .i dirfd is specified as .br at_fdcwd . .ip applications that employ the .b resolve_no_xdev flag are encouraged to make its use configurable (unless it is used for a specific security purpose), as bind mounts are widely used by end-users. setting this flag indiscriminately\(emi.e., for purposes not specifically related to security\(emfor all uses of .br openat2 () may result in spurious errors on previously functional systems. this may occur if, for example, a system pathname that is used by an application is modified (e.g., in a new distribution release) so that a pathname component (now) contains a bind mount. .tp .b resolve_cached make the open operation fail unless all path components are already present in the kernel's lookup cache. if any kind of revalidation or i/o is needed to satisfy the lookup, .br openat2 () fails with the error .b eagain . this is useful in providing a fast-path open that can be performed without resorting to thread offload, or other mechanisms that an application might use to offload slower operations. .re .ip if any bits other than those listed above are set in .ir how.resolve , an error is returned. .sh return value on success, a new file descriptor is returned. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors the set of errors returned by .br openat2 () includes all of the errors returned by .br openat (2), as well as the following additional errors: .tp .b e2big an extension that this kernel does not support was specified in .ir how . (see the "extensibility" section of .b notes for more detail on how extensions are handled.) .tp .b eagain .i how.resolve contains either .br resolve_in_root or .br resolve_beneath , and the kernel could not ensure that a ".." component didn't escape (due to a race condition or potential attack). the caller may choose to retry the .br openat2 () call. .tp .b eagain .br resolve_cached was set, and the open operation cannot be performed using only cached information. the caller should retry without .b resolve_cached set in .i how.resolve . .tp .b einval an unknown flag or invalid value was specified in .ir how . .tp .b einval .i mode is nonzero, but .i how.flags does not contain .br o_creat or .br o_tmpfile . .tp .b einval .i size was smaller than any known version of .ir "struct open_how" . .tp .b eloop .i how.resolve contains .br resolve_no_symlinks , and one of the path components was a symbolic link (or magic link). .tp .b eloop .i how.resolve contains .br resolve_no_magiclinks , and one of the path components was a magic link. .tp .b exdev .i how.resolve contains either .br resolve_in_root or .br resolve_beneath , and an escape from the root during path resolution was detected. .tp .b exdev .i how.resolve contains .br resolve_no_xdev , and a path component crosses a mount point. .sh versions .br openat2 () first appeared in linux 5.6. .\" commit fddb5d430ad9fa91b49b1d34d0202ffe2fa0e179 .sh conforming to this system call is linux-specific. .pp the semantics of .b resolve_beneath were modeled after freebsd's .br o_beneath . .sh notes .ss extensibility in order to allow for future extensibility, .br openat2 () requires the user-space application to specify the size of the .i open_how structure that it is passing. by providing this information, it is possible for .br openat2 () to provide both forwards- and backwards-compatibility, with .i size acting as an implicit version number. (because new extension fields will always be appended, the structure size will always increase.) this extensibility design is very similar to other system calls such as .br sched_setattr (2), .br perf_event_open (2), and .br clone3 (2). .pp if we let .i usize be the size of the structure as specified by the user-space application, and .i ksize be the size of the structure which the kernel supports, then there are three cases to consider: .ip \(bu 2 if .ir ksize equals .ir usize , then there is no version mismatch and .i how can be used verbatim. .ip \(bu if .ir ksize is larger than .ir usize , then there are some extension fields that the kernel supports which the user-space application is unaware of. because a zero value in any added extension field signifies a no-op, the kernel treats all of the extension fields not provided by the user-space application as having zero values. this provides backwards-compatibility. .ip \(bu if .ir ksize is smaller than .ir usize , then there are some extension fields which the user-space application is aware of but which the kernel does not support. because any extension field must have its zero values signify a no-op, the kernel can safely ignore the unsupported extension fields if they are all-zero. if any unsupported extension fields are nonzero, then \-1 is returned and .i errno is set to .br e2big . this provides forwards-compatibility. .pp because the definition of .i struct open_how may change in the future (with new fields being added when system headers are updated), user-space applications should zero-fill .i struct open_how to ensure that recompiling the program with new headers will not result in spurious errors at runtime. the simplest way is to use a designated initializer: .pp .in +4n .ex struct open_how how = { .flags = o_rdwr, .resolve = resolve_in_root }; .ee .in .pp or explicitly using .br memset (3) or similar: .pp .in +4n .ex struct open_how how; memset(&how, 0, sizeof(how)); how.flags = o_rdwr; how.resolve = resolve_in_root; .ee .in .pp a user-space application that wishes to determine which extensions the running kernel supports can do so by conducting a binary search on .ir size with a structure which has every byte nonzero (to find the largest value which doesn't produce an error of .br e2big ). .sh see also .br openat (2), .br path_resolution (7), .br symlink (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/resolver.3 .so man2/unlink.2 .so man3/envz_add.3 .so man3/rpc.3 .so man3/mq_timedreceive.3 .\" because mq_timedreceive(3) is layered on a system call of the same name .so man3/setjmp.3 .\" this man page was written by jeremy phelps . .\" .\" %%%license_start(freely_redistributable) .\" redistribute and modify at will. .\" %%%license_end .\" .th getpt 3 2021-03-22 "gnu" "linux programmer's manual" .sh name getpt \- open a new pseudoterminal master .sh synopsis .nf .br "#define _gnu_source" " /* see feature_test_macros(7) */" .b #include .pp .b "int getpt(void);" .fi .sh description .br getpt () opens a new pseudoterminal device and returns a file descriptor that refers to that device. it is equivalent to opening the pseudoterminal multiplexor device .pp .in +4n .ex open("/dev/ptmx", o_rdwr); .ee .in .pp on linux systems, though the pseudoterminal multiplexor device is located elsewhere on some systems that use the gnu c library. .sh return value .br getpt () returns an open file descriptor upon successful completion. otherwise, it returns \-1 and sets .i errno to indicate the error. .sh errors .br getpt () can fail with various errors described in .br open (2). .sh versions .br getpt () is provided in glibc since version 2.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br getpt () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to .br getpt () is glibc-specific; use .br posix_openpt (3) instead. .sh see also .br grantpt (3), .br posix_openpt (3), .br ptsname (3), .br unlockpt (3), .br ptmx (4), .br pty (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1980, 1991 regents of the university of california. .\" all rights reserved. .\" .\" %%%license_start(bsd_4_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. all advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" this product includes software developed by the university of .\" california, berkeley and its contributors. .\" 4. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" @(#)ioctl.2 6.4 (berkeley) 3/10/91 .\" .\" modified 1993-07-23 by rik faith .\" modified 1996-10-22 by eric s. raymond .\" modified 1999-06-25 by rachael munns .\" modified 2000-09-21 by andries brouwer .\" .th ioctl 2 2021-03-22 "linux" "linux programmer's manual" .sh name ioctl \- control device .sh synopsis .nf .b #include .pp .bi "int ioctl(int " fd ", unsigned long " request ", ...);" .\" posix says 'request' is int, but glibc has the above .\" see https://bugzilla.kernel.org/show_bug.cgi?id=42705 .fi .sh description the .br ioctl () system call manipulates the underlying device parameters of special files. in particular, many operating characteristics of character special files (e.g., terminals) may be controlled with .br ioctl () requests. the argument .i fd must be an open file descriptor. .pp the second argument is a device-dependent request code. the third argument is an untyped pointer to memory. it's traditionally .bi "char *" argp (from the days before .b "void *" was valid c), and will be so named for this discussion. .pp an .br ioctl () .i request has encoded in it whether the argument is an .i in parameter or .i out parameter, and the size of the argument .i argp in bytes. macros and defines used in specifying an .br ioctl () .i request are located in the file .ir . see notes. .sh return value usually, on success zero is returned. a few .br ioctl () requests use the return value as an output parameter and return a nonnegative value on success. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b ebadf .i fd is not a valid file descriptor. .tp .b efault .i argp references an inaccessible memory area. .tp .b einval .i request or .i argp is not valid. .tp .b enotty .i fd is not associated with a character special device. .tp .b enotty the specified request does not apply to the kind of object that the file descriptor .i fd references. .sh conforming to no single standard. arguments, returns, and semantics of .br ioctl () vary according to the device driver in question (the call is used as a catch-all for operations that don't cleanly fit the unix stream i/o model). .pp the .br ioctl () system call appeared in version 7 at&t unix. .sh notes in order to use this call, one needs an open file descriptor. often the .br open (2) call has unwanted side effects, that can be avoided under linux by giving it the .b o_nonblock flag. .\" .ss ioctl structure .\" added two sections - aeb ioctl command values are 32-bit constants. in principle these constants are completely arbitrary, but people have tried to build some structure into them. .pp the old linux situation was that of mostly 16-bit constants, where the last byte is a serial number, and the preceding byte(s) give a type indicating the driver. sometimes the major number was used: 0x03 for the .b hdio_* ioctls, 0x06 for the .b lp* ioctls. and sometimes one or more ascii letters were used. for example, .b tcgets has value 0x00005401, with 0x54 = \(aqt\(aq indicating the terminal driver, and .b cygettimeout has value 0x00435906, with 0x43 0x59 = \(aqc\(aq \(aqy\(aq indicating the cyclades driver. .pp later (0.98p5) some more information was built into the number. one has 2 direction bits (00: none, 01: write, 10: read, 11: read/write) followed by 14 size bits (giving the size of the argument), followed by an 8-bit type (collecting the ioctls in groups for a common purpose or a common driver), and an 8-bit serial number. .pp the macros describing this structure live in .i and are .b _io(type,nr) and .br "{_ior,_iow,_iowr}(type,nr,size)" . they use .i sizeof(size) so that size is a misnomer here: this third argument is a data type. .pp note that the size bits are very unreliable: in lots of cases they are wrong, either because of buggy macros using .ir sizeof(sizeof(struct)) , or because of legacy values. .pp thus, it seems that the new structure only gave disadvantages: it does not help in checking, but it causes varying values for the various architectures. .sh see also .br execve (2), .br fcntl (2), .br ioctl_console (2), .br ioctl_fat (2), .br ioctl_ficlonerange (2), .br ioctl_fideduperange (2), .br ioctl_fslabel (2), .br ioctl_getfsmap (2), .br ioctl_iflags (2), .br ioctl_ns (2), .br ioctl_tty (2), .br ioctl_userfaultfd (2), .br open (2), .\" .br mt (4), .br sd (4), .br tty (4) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2012, petr benas .\" and copyright (c) 2012, michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of .\" this manual under the conditions for verbatim copying, provided that .\" the entire resulting derived work is distributed under the terms of .\" a permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume .\" no responsibility for errors or omissions, or for damages resulting .\" from the use of the information contained herein. the author(s) may .\" not have taken the same level of care in the production of this .\" manual, which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th get_nprocs 3 2021-03-22 "gnu" "linux programmer's manual" .sh name get_nprocs, get_nprocs_conf \- get number of processors .sh synopsis .nf .b #include .pp .bi "int get_nprocs(void);" .bi "int get_nprocs_conf(void);" .fi .sh description the function .br get_nprocs_conf () returns the number of processors configured by the operating system. .pp the function .br get_nprocs () returns the number of processors currently available in the system. this may be less than the number returned by .br get_nprocs_conf () because processors may be offline (e.g., on hotpluggable systems). .sh return value as given in description. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br get_nprocs (), .br get_nprocs_conf () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to these functions are gnu extensions. .sh notes the current .\" glibc 2.15 implementation of these functions is rather expensive, since they open and parse files in the .i /sys filesystem each time they are called. .pp the following .br sysconf (3) calls make use of the functions documented on this page to return the same information. .pp .in +4n .ex np = sysconf(_sc_nprocessors_conf); /* processors configured */ np = sysconf(_sc_nprocessors_onln); /* processors available */ .ee .in .sh examples the following example shows how .br get_nprocs () and .br get_nprocs_conf () can be used. .pp .ex #include #include #include int main(int argc, char *argv[]) { printf("this system has %d processors configured and " "%d processors available.\en", get_nprocs_conf(), get_nprocs()); exit(exit_success); } .ee .sh see also .br nproc (1) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/setjmp.3 .so man3/getutent.3 .\" %%%license_start(public_domain) .\" this page is in the public domain .\" %%%license_end .\" .th tzselect 8 2021-03-22 "" "linux system administration" .sh name tzselect \- select a timezone .sh synopsis .nf .b tzselect .fi .sh description the .b tzselect program asks the user for information about the current location, and outputs the resulting timezone description to standard output. the output is suitable as a value for the .b tz environment variable. .pp all interaction with the user is done via standard input and standard error. .sh exit status the exit status is zero if a timezone was successfully obtained from the user, and is nonzero otherwise. .sh environment .tp .b awk name of a posix-compliant .i awk program (default: .br awk ). .tp .b tzdir name of the directory containing timezone data files (default: .ir /usr/share/zoneinfo ). .\" or perhaps /usr/local/etc/zoneinfo in some older systems. .sh files .tp \fbtzdir\fp\fi/iso3166.tab\fp table of iso 3166 2-letter country codes and country names. .tp \fbtzdir\fp\fi/zone.tab\fp table of country codes, latitude and longitude, tz values, and descriptive comments. .tp \fbtzdir\fp\fi/\fp\fitz\fp timezone data file for timezone .ir tz . .sh see also .br tzfile (5), .br zdump (8), .br zic (8) .\" @(#)tzselect.8 1.3 .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/cmsg.3 .so man7/system_data_types.7 .so man3/fma.3 .so man2/outb.2 .so man3/fenv.3 .so man3/unlocked_stdio.3 .\" copyright (c) bruno haible .\" and copyright (c) 2014 michael kerrisk .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th towlower 3 2021-03-22 "gnu" "linux programmer's manual" .sh name towlower, towlower_l \- convert a wide character to lowercase .sh synopsis .nf .b #include .pp .bi "wint_t towlower(wint_t " wc ); .bi "wint_t towlower_l(wint_t " wc ", locale_t " locale ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br towlower_l (): .nf since glibc 2.10: _xopen_source >= 700 before glibc 2.10: _gnu_source .fi .sh description the .br towlower () function is the wide-character equivalent of the .br tolower (3) function. if .i wc is an uppercase wide character, and there exists a lowercase equivalent in the current locale, it returns the lowercase equivalent of .ir wc . in all other cases, .i wc is returned unchanged. .pp the .br towlower_l () function performs the same task, but performs the conversion based on the character type information in the locale specified by .ir locale . the behavior of .br towlower_l () is undefined if .i locale is the special locale object .b lc_global_locale (see .br duplocale (3)) or is not a valid locale object handle. .pp the argument .i wc must be representable as a .i wchar_t and be a valid character in the locale or be the value .br weof . .sh return value if .i wc was convertible to lowercase, .br towlower () returns its lowercase equivalent; otherwise it returns .ir wc . .sh versions the .br towlower_l () function first appeared in glibc 2.3. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br towlower () t} thread safety mt-safe locale t{ .br towlower_l () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to .br towlower (): c99, posix.1-2001 (xsi); present as an xsi extension in posix.1-2008, but marked obsolete. .pp .br towlower_l (): posix.1-2008. .sh notes the behavior of these functions depends on the .b lc_ctype category of the locale. .pp these functions are not very appropriate for dealing with unicode characters, because unicode knows about three cases: upper, lower, and title case. .sh see also .br iswlower (3), .br towctrans (3), .br towupper (3), .br locale (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" this man page is copyright (c) 1999 andi kleen . .\" .\" %%%license_start(verbatim_one_para) .\" permission is granted to distribute possibly modified copies .\" of this page provided the header is included verbatim, .\" and in case of nontrivial modification author and date .\" of the modification is added to the header. .\" %%%license_end .\" .\" $id: packet.7,v 1.13 2000/08/14 08:03:45 ak exp $ .\" .th packet 7 2021-03-22 "linux" "linux programmer's manual" .sh name packet \- packet interface on device level .sh synopsis .nf .b #include .b #include .b #include /* the l2 protocols */ .pp .bi "packet_socket = socket(af_packet, int " socket_type ", int "protocol ); .fi .sh description packet sockets are used to receive or send raw packets at the device driver (osi layer 2) level. they allow the user to implement protocol modules in user space on top of the physical layer. .pp the .i socket_type is either .b sock_raw for raw packets including the link-level header or .b sock_dgram for cooked packets with the link-level header removed. the link-level header information is available in a common format in a .ir sockaddr_ll structure. .i protocol is the ieee 802.3 protocol number in network byte order. see the .i include file for a list of allowed protocols. when protocol is set to .br htons(eth_p_all) , then all protocols are received. all incoming packets of that protocol type will be passed to the packet socket before they are passed to the protocols implemented in the kernel. .pp in order to create a packet socket, a process must have the .b cap_net_raw capability in the user namespace that governs its network namespace. .pp .b sock_raw packets are passed to and from the device driver without any changes in the packet data. when receiving a packet, the address is still parsed and passed in a standard .i sockaddr_ll address structure. when transmitting a packet, the user-supplied buffer should contain the physical-layer header. that packet is then queued unmodified to the network driver of the interface defined by the destination address. some device drivers always add other headers. .b sock_raw is similar to but not compatible with the obsolete .b af_inet/sock_packet of linux 2.0. .pp .b sock_dgram operates on a slightly higher level. the physical header is removed before the packet is passed to the user. packets sent through a .b sock_dgram packet socket get a suitable physical-layer header based on the information in the .i sockaddr_ll destination address before they are queued. .pp by default, all packets of the specified protocol type are passed to a packet socket. to get packets only from a specific interface use .br bind (2) specifying an address in a .i struct sockaddr_ll to bind the packet socket to an interface. fields used for binding are .ir sll_family (should be .br af_packet ), .ir sll_protocol , and .ir sll_ifindex . .pp the .br connect (2) operation is not supported on packet sockets. .pp when the .b msg_trunc flag is passed to .br recvmsg (2), .br recv (2), or .br recvfrom (2), the real length of the packet on the wire is always returned, even when it is longer than the buffer. .ss address types the .i sockaddr_ll structure is a device-independent physical-layer address. .pp .in +4n .ex struct sockaddr_ll { unsigned short sll_family; /* always af_packet */ unsigned short sll_protocol; /* physical\-layer protocol */ int sll_ifindex; /* interface number */ unsigned short sll_hatype; /* arp hardware type */ unsigned char sll_pkttype; /* packet type */ unsigned char sll_halen; /* length of address */ unsigned char sll_addr[8]; /* physical\-layer address */ }; .ee .in .pp the fields of this structure are as follows: .ip * 3 .i sll_protocol is the standard ethernet protocol type in network byte order as defined in the .i include file. it defaults to the socket's protocol. .ip * .i sll_ifindex is the interface index of the interface (see .br netdevice (7)); 0 matches any interface (only permitted for binding). .i sll_hatype is an arp type as defined in the .i include file. .ip * .i sll_pkttype contains the packet type. valid types are .b packet_host for a packet addressed to the local host, .b packet_broadcast for a physical-layer broadcast packet, .b packet_multicast for a packet sent to a physical-layer multicast address, .b packet_otherhost for a packet to some other host that has been caught by a device driver in promiscuous mode, and .b packet_outgoing for a packet originating from the local host that is looped back to a packet socket. these types make sense only for receiving. .ip * .i sll_addr and .i sll_halen contain the physical-layer (e.g., ieee 802.3) address and its length. the exact interpretation depends on the device. .pp when you send packets, it is enough to specify .ir sll_family , .ir sll_addr , .ir sll_halen , .ir sll_ifindex , and .ir sll_protocol . the other fields should be 0. .i sll_hatype and .i sll_pkttype are set on received packets for your information. .ss socket options packet socket options are configured by calling .br setsockopt (2) with level .br sol_packet . .tp .br packet_add_membership .pd 0 .tp .br packet_drop_membership .pd packet sockets can be used to configure physical-layer multicasting and promiscuous mode. .b packet_add_membership adds a binding and .b packet_drop_membership drops it. they both expect a .i packet_mreq structure as argument: .ip .in +4n .ex struct packet_mreq { int mr_ifindex; /* interface index */ unsigned short mr_type; /* action */ unsigned short mr_alen; /* address length */ unsigned char mr_address[8]; /* physical\-layer address */ }; .ee .in .ip .i mr_ifindex contains the interface index for the interface whose status should be changed. the .i mr_type field specifies which action to perform. .b packet_mr_promisc enables receiving all packets on a shared medium (often known as "promiscuous mode"), .b packet_mr_multicast binds the socket to the physical-layer multicast group specified in .i mr_address and .ir mr_alen , and .b packet_mr_allmulti sets the socket up to receive all multicast packets arriving at the interface. .ip in addition, the traditional ioctls .br siocsifflags , .br siocaddmulti , .b siocdelmulti can be used for the same purpose. .tp .br packet_auxdata " (since linux 2.6.21)" .\" commit 8dc4194474159660d7f37c495e3fc3f10d0db8cc if this binary option is enabled, the packet socket passes a metadata structure along with each packet in the .br recvmsg (2) control field. the structure can be read with .br cmsg (3). it is defined as .ip .in +4n .ex struct tpacket_auxdata { __u32 tp_status; __u32 tp_len; /* packet length */ __u32 tp_snaplen; /* captured length */ __u16 tp_mac; __u16 tp_net; __u16 tp_vlan_tci; __u16 tp_vlan_tpid; /* since linux 3.14; earlier, these were unused padding bytes */ .\" commit a0cdfcf39362410d5ea983f4daf67b38de129408 added tp_vlan_tpid }; .ee .in .tp .br packet_fanout " (since linux 3.1)" .\" commit dc99f600698dcac69b8f56dda9a8a00d645c5ffc to scale processing across threads, packet sockets can form a fanout group. in this mode, each matching packet is enqueued onto only one socket in the group. a socket joins a fanout group by calling .br setsockopt (2) with level .b sol_packet and option .br packet_fanout . each network namespace can have up to 65536 independent groups. a socket selects a group by encoding the id in the first 16 bits of the integer option value. the first packet socket to join a group implicitly creates it. to successfully join an existing group, subsequent packet sockets must have the same protocol, device settings, fanout mode, and flags (see below). packet sockets can leave a fanout group only by closing the socket. the group is deleted when the last socket is closed. .ip fanout supports multiple algorithms to spread traffic between sockets, as follows: .rs .ip * 3 the default mode, .br packet_fanout_hash , sends packets from the same flow to the same socket to maintain per-flow ordering. for each packet, it chooses a socket by taking the packet flow hash modulo the number of sockets in the group, where a flow hash is a hash over network-layer address and optional transport-layer port fields. .ip * the load-balance mode .br packet_fanout_lb implements a round-robin algorithm. .ip * .br packet_fanout_cpu selects the socket based on the cpu that the packet arrived on. .ip * .br packet_fanout_rollover processes all data on a single socket, moving to the next when one becomes backlogged. .ip * .br packet_fanout_rnd selects the socket using a pseudo-random number generator. .ip * .br packet_fanout_qm .\" commit 2d36097d26b5991d71a2cf4a20c1a158f0f1bfcd (available since linux 3.14) selects the socket using the recorded queue_mapping of the received skb. .re .ip fanout modes can take additional options. ip fragmentation causes packets from the same flow to have different flow hashes. the flag .br packet_fanout_flag_defrag , if set, causes packets to be defragmented before fanout is applied, to preserve order even in this case. fanout mode and options are communicated in the second 16 bits of the integer option value. the flag .br packet_fanout_flag_rollover enables the roll over mechanism as a backup strategy: if the original fanout algorithm selects a backlogged socket, the packet rolls over to the next available one. .tp .br packet_loss " (with " packet_tx_ring ) when a malformed packet is encountered on a transmit ring, the default is to reset its .i tp_status to .br tp_status_wrong_format and abort the transmission immediately. the malformed packet blocks itself and subsequently enqueued packets from being sent. the format error must be fixed, the associated .i tp_status reset to .br tp_status_send_request , and the transmission process restarted via .br send (2). however, if .br packet_loss is set, any malformed packet will be skipped, its .i tp_status reset to .br tp_status_available , and the transmission process continued. .tp .br packet_reserve " (with " packet_rx_ring ) by default, a packet receive ring writes packets immediately following the metadata structure and alignment padding. this integer option reserves additional headroom. .tp .br packet_rx_ring create a memory-mapped ring buffer for asynchronous packet reception. the packet socket reserves a contiguous region of application address space, lays it out into an array of packet slots and copies packets (up to .ir tp_snaplen ) into subsequent slots. each packet is preceded by a metadata structure similar to .ir tpacket_auxdata . the protocol fields encode the offset to the data from the start of the metadata header. .i tp_net stores the offset to the network layer. if the packet socket is of type .br sock_dgram , then .i tp_mac is the same. if it is of type .br sock_raw , then that field stores the offset to the link-layer frame. packet socket and application communicate the head and tail of the ring through the .i tp_status field. the packet socket owns all slots with .i tp_status equal to .br tp_status_kernel . after filling a slot, it changes the status of the slot to transfer ownership to the application. during normal operation, the new .i tp_status value has at least the .br tp_status_user bit set to signal that a received packet has been stored. when the application has finished processing a packet, it transfers ownership of the slot back to the socket by setting .i tp_status equal to .br tp_status_kernel . .ip packet sockets implement multiple variants of the packet ring. the implementation details are described in .ir documentation/networking/packet_mmap.rst in the linux kernel source tree. .tp .br packet_statistics retrieve packet socket statistics in the form of a structure .ip .in +4n .ex struct tpacket_stats { unsigned int tp_packets; /* total packet count */ unsigned int tp_drops; /* dropped packet count */ }; .ee .in .ip receiving statistics resets the internal counters. the statistics structure differs when using a ring of variant .br tpacket_v3 . .tp .br packet_timestamp " (with " packet_rx_ring "; since linux 2.6.36)" .\" commit 614f60fa9d73a9e8fdff3df83381907fea7c5649 the packet receive ring always stores a timestamp in the metadata header. by default, this is a software generated timestamp generated when the packet is copied into the ring. this integer option selects the type of timestamp. besides the default, it support the two hardware formats described in .ir documentation/networking/timestamping.rst in the linux kernel source tree. .tp .br packet_tx_ring " (since linux 2.6.31)" .\" commit 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 create a memory-mapped ring buffer for packet transmission. this option is similar to .br packet_rx_ring and takes the same arguments. the application writes packets into slots with .i tp_status equal to .br tp_status_available and schedules them for transmission by changing .i tp_status to .br tp_status_send_request . when packets are ready to be transmitted, the application calls .br send (2) or a variant thereof. the .i buf and .i len fields of this call are ignored. if an address is passed using .br sendto (2) or .br sendmsg (2), then that overrides the socket default. on successful transmission, the socket resets .i tp_status to .br tp_status_available . it immediately aborts the transmission on error unless .br packet_loss is set. .tp .br packet_version " (with " packet_rx_ring "; since linux 2.6.27)" .\" commit bbd6ef87c544d88c30e4b762b1b61ef267a7d279 by default, .br packet_rx_ring creates a packet receive ring of variant .br tpacket_v1 . to create another variant, configure the desired variant by setting this integer option before creating the ring. .tp .br packet_qdisc_bypass " (since linux 3.14)" .\" commit d346a3fae3ff1d99f5d0c819bf86edf9094a26a1 by default, packets sent through packet sockets pass through the kernel's qdisc (traffic control) layer, which is fine for the vast majority of use cases. for traffic generator appliances using packet sockets that intend to brute-force flood the network\(emfor example, to test devices under load in a similar fashion to pktgen\(emthis layer can be bypassed by setting this integer option to 1. a side effect is that packet buffering in the qdisc layer is avoided, which will lead to increased drops when network device transmit queues are busy; therefore, use at your own risk. .ss ioctls .b siocgstamp can be used to receive the timestamp of the last received packet. argument is a .i struct timeval variable. .\" fixme document siocgstampns .pp in addition, all standard ioctls defined in .br netdevice (7) and .br socket (7) are valid on packet sockets. .ss error handling packet sockets do no error handling other than errors occurred while passing the packet to the device driver. they don't have the concept of a pending error. .sh errors .tp .b eaddrnotavail unknown multicast group address passed. .tp .b efault user passed invalid memory address. .tp .b einval invalid argument. .tp .b emsgsize packet is bigger than interface mtu. .tp .b enetdown interface is not up. .tp .b enobufs not enough memory to allocate the packet. .tp .b enodev unknown device name or interface index specified in interface address. .tp .b enoent no packet received. .tp .b enotconn no interface address passed. .tp .b enxio interface address contained an invalid interface index. .tp .b eperm user has insufficient privileges to carry out this operation. .pp in addition, other errors may be generated by the low-level driver. .sh versions .b af_packet is a new feature in linux 2.2. earlier linux versions supported only .br sock_packet . .sh notes for portable programs it is suggested to use .b af_packet via .br pcap (3); although this covers only a subset of the .b af_packet features. .pp the .b sock_dgram packet sockets make no attempt to create or parse the ieee 802.2 llc header for a ieee 802.3 frame. when .b eth_p_802_3 is specified as protocol for sending the kernel creates the 802.3 frame and fills out the length field; the user has to supply the llc header to get a fully conforming packet. incoming 802.3 packets are not multiplexed on the dsap/ssap protocol fields; instead they are supplied to the user as protocol .b eth_p_802_2 with the llc header prefixed. it is thus not possible to bind to .br eth_p_802_3 ; bind to .b eth_p_802_2 instead and do the protocol multiplex yourself. the default for sending is the standard ethernet dix encapsulation with the protocol filled in. .pp packet sockets are not subject to the input or output firewall chains. .ss compatibility in linux 2.0, the only way to get a packet socket was with the call: .pp socket(af_inet, sock_packet, protocol) .pp this is still supported, but deprecated and strongly discouraged. the main difference between the two methods is that .b sock_packet uses the old .i struct sockaddr_pkt to specify an interface, which doesn't provide physical-layer independence. .pp .in +4n .ex struct sockaddr_pkt { unsigned short spkt_family; unsigned char spkt_device[14]; unsigned short spkt_protocol; }; .ee .in .pp .i spkt_family contains the device type, .i spkt_protocol is the ieee 802.3 protocol type as defined in .i and .i spkt_device is the device name as a null-terminated string, for example, eth0. .pp this structure is obsolete and should not be used in new code. .sh bugs the ieee 802.2/803.3 llc handling could be considered as a bug. .pp socket filters are not documented. .pp the .b msg_trunc .br recvmsg (2) extension is an ugly hack and should be replaced by a control message. there is currently no way to get the original destination address of packets via .br sock_dgram . .\" .sh credits .\" this man page was written by andi kleen with help from matthew wilcox. .\" af_packet in linux 2.2 was implemented .\" by alexey kuznetsov, based on code by alan cox and others. .sh see also .br socket (2), .br pcap (3), .br capabilities (7), .br ip (7), .br raw (7), .br socket (7) .pp rfc\ 894 for the standard ip ethernet encapsulation. rfc\ 1700 for the ieee 802.3 ip encapsulation. .pp the .i include file for physical-layer protocols. .pp the linux kernel source tree. .ir documentation/networking/filter.rst describes how to apply berkeley packet filters to packet sockets. .ir tools/testing/selftests/net/psock_tpacket.c contains example source code for all available versions of .br packet_rx_ring and .br packet_tx_ring . .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/setresgid.2 .so man3/rpc.3 .\" copyright (c) 1993 michael haardt (michael@moria.de), .\" fri apr 2 11:32:09 met dst 1993 .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .\" modified sat jul 24 17:19:57 1993 by rik faith (faith@cs.unc.edu) .th intro 6 2007-10-23 "linux" "linux programmer's manual" .sh name intro \- introduction to games .sh description section 6 of the manual describes the games and funny little programs available on the system. .sh notes .ss authors and copyright conditions look at the header of the manual page source for the author(s) and copyright conditions. note that these can be different from page to page! .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2000 manoj srivastava .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .\" minor polishing, aeb .\" modified, 2002-06-16, mike coleman .\" .th hosts 5 2021-03-22 "linux" "linux programmer's manual" .sh name hosts \- static table lookup for hostnames .sh synopsis .nf .b /etc/hosts .fi .sh description this manual page describes the format of the .i /etc/hosts file. this file is a simple text file that associates ip addresses with hostnames, one line per ip address. for each host a single line should be present with the following information: .rs .pp ip_address canonical_hostname [aliases...] .re .pp the ip address can conform to either ipv4 or ipv6. fields of the entry are separated by any number of blanks and/or tab characters. text from a "#" character until the end of the line is a comment, and is ignored. host names may contain only alphanumeric characters, minus signs ("\-"), and periods ("."). they must begin with an alphabetic character and end with an alphanumeric character. optional aliases provide for name changes, alternate spellings, shorter hostnames, or generic hostnames (for example, .ir localhost ). if required, a host may have two separate entries in this file; one for each version of the internet protocol (ipv4 and ipv6). .pp the berkeley internet name domain (bind) server implements the internet name server for unix systems. it augments or replaces the .i /etc/hosts file or hostname lookup, and frees a host from relying on .i /etc/hosts being up to date and complete. .pp in modern systems, even though the host table has been superseded by dns, it is still widely used for: .tp .b bootstrapping most systems have a small host table containing the name and address information for important hosts on the local network. this is useful when dns is not running, for example during system bootup. .tp .b nis sites that use nis use the host table as input to the nis host database. even though nis can be used with dns, most nis sites still use the host table with an entry for all local hosts as a backup. .tp .b isolated nodes very small sites that are isolated from the network use the host table instead of dns. if the local information rarely changes, and the network is not connected to the internet, dns offers little advantage. .sh files .i /etc/hosts .sh notes modifications to this file normally take effect immediately, except in cases where the file is cached by applications. .ss historical notes rfc\ 952 gave the original format for the host table, though it has since changed. .pp before the advent of dns, the host table was the only way of resolving hostnames on the fledgling internet. indeed, this file could be created from the official host data base maintained at the network information control center (nic), though local changes were often required to bring it up to date regarding unofficial aliases and/or unknown hosts. the nic no longer maintains the hosts.txt files, though looking around at the time of writing (circa 2000), there are historical hosts.txt files on the www. i just found three, from 92, 94, and 95. .sh examples .ex # the following lines are desirable for ipv4 capable hosts 127.0.0.1 localhost # 127.0.1.1 is often used for the fqdn of the machine 127.0.1.1 thishost.mydomain.org thishost 192.168.1.10 foo.mydomain.org foo 192.168.1.13 bar.mydomain.org bar 146.82.138.7 master.debian.org master 209.237.226.90 www.opensource.org # the following lines are desirable for ipv6 capable hosts ::1 localhost ip6\-localhost ip6\-loopback ff02::1 ip6\-allnodes ff02::2 ip6\-allrouters .ee .sh see also .br hostname (1), .br resolver (3), .br host.conf (5), .br resolv.conf (5), .br resolver (5), .br hostname (7), .br named (8) .pp internet rfc\ 952 .\" .sh author .\" this manual page was written by manoj srivastava , .\" for the debian gnu/linux system. .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2012 by michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th malloc_stats 3 2021-03-22 "linux" "linux programmer's manual" .sh name malloc_stats \- print memory allocation statistics .sh synopsis .nf .b #include .pp .b void malloc_stats(void); .fi .sh description the .br malloc_stats () function prints (on standard error) statistics about memory allocated by .br malloc (3) and related functions. for each arena (allocation area), this function prints the total amount of memory allocated and the total number of bytes consumed by in-use allocations. (these two values correspond to the .i arena and .i uordblks fields retrieved by .br mallinfo (3).) in addition, the function prints the sum of these two statistics for all arenas, and the maximum number of blocks and bytes that were ever simultaneously allocated using .br mmap (2). .\" .sh versions .\" available already in glibc 2.0, possibly earlier .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br malloc_stats () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to this function is a gnu extension. .sh notes more detailed information about memory allocations in the main arena can be obtained using .br mallinfo (3). .sh see also .br mmap (2), .br mallinfo (3), .br malloc (3), .br malloc_info (3), .br mallopt (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2014 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th inet_net_pton 3 2021-03-22 "linux" "linux programmer's manual" .sh name inet_net_pton, inet_net_ntop \- internet network number conversion .sh synopsis .nf .b #include .pp .bi "int inet_net_pton(int " af ", const char *" pres , .bi " void *" netp ", size_t " nsize ); .bi "char *inet_net_ntop(int " af ", const void *" netp ", int " bits , .bi " char *" pres ", size_t " psize ); .fi .pp link with \fi\-lresolv\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br inet_net_pton (), .br inet_net_ntop (): .nf since glibc 2.20: _default_source before glibc 2.20: _bsd_source || _svid_source .fi .sh description these functions convert network numbers between presentation (i.e., printable) format and network (i.e., binary) format. .pp for both functions, .i af specifies the address family for the conversion; the only supported value is .br af_inet . .ss inet_net_pton() the .br inet_net_pton () function converts .ir pres , a null-terminated string containing an internet network number in presentation format to network format. the result of the conversion, which is in network byte order, is placed in the buffer pointed to by .ir net . (the .i netp argument typically points to an .i in_addr structure.) the .i nsize argument specifies the number of bytes available in .ir netp . .pp on success, .br inet_net_pton () returns the number of bits in the network number field of the result placed in .ir netp . for a discussion of the input presentation format and the return value, see notes. .pp .ir note : the buffer pointed to by .i netp should be zeroed out before calling .br inet_net_pton (), since the call writes only as many bytes as are required for the network number (or as are explicitly specified by .ir pres ), which may be less than the number of bytes in a complete network address. .ss inet_net_ntop() the .br inet_net_ntop () function converts the network number in the buffer pointed to by .ir netp to presentation format; .i *netp is interpreted as a value in network byte order. the .i bits argument specifies the number of bits in the network number in .ir *netp . .pp the null-terminated presentation-format string is placed in the buffer pointed to by .ir pres . the .i psize argument specifies the number of bytes available in .ir pres . the presentation string is in cidr format: a dotted-decimal number representing the network address, followed by a slash, and the size of the network number in bits. .sh return value on success, .br inet_net_pton () returns the number of bits in the network number. on error, it returns \-1, and .i errno is set to indicate the error. .pp on success, .br inet_net_ntop () returns .ir pres . on error, it returns null, and .i errno is set to indicate the error. .sh errors .tp .b eafnosupport .i af specified a value other than .br af_inet . .tp .b emsgsize the size of the output buffer was insufficient. .tp .b enoent .rb ( inet_net_pton ()) .ir pres was not in correct presentation format. .sh conforming to the .br inet_net_pton () and .br inet_net_ntop () functions are nonstandard, but widely available. .sh notes .ss input presentation format for inet_net_pton() the network number may be specified either as a hexadecimal value or in dotted-decimal notation. .pp hexadecimal values are indicated by an initial "0x" or "0x". the hexadecimal digits populate the nibbles (half octets) of the network number from left to right in network byte order. .\" if the hexadecimal string is short, the remaining nibbles are zeroed. .pp in dotted-decimal notation, up to four octets are specified, as decimal numbers separated by dots. thus, any of the following forms are accepted: .pp a.b.c.d a.b.c a.b a .pp each part is a number in the range 0 to 255 that populates one byte of the resulting network number, going from left to right, in network-byte (big endian) order. where a part is omitted, the resulting byte in the network number is zero. .\" reading other man pages, some other implementations treat .\" 'c' in a.b.c as a 16-bit number that populates right-most two bytes .\" 'b' in a.b as a 24-bit number that populates right-most three bytes .pp for either hexadecimal or dotted-decimal format, the network number can optionally be followed by a slash and a number in the range 0 to 32, which specifies the size of the network number in bits. .ss return value of inet_net_pton() the return value of .br inet_net_pton () is the number of bits in the network number field. if the input presentation string terminates with a slash and an explicit size value, then that size becomes the return value of .br inet_net_pton (). otherwise, the return value, .ir bits , is inferred as follows: .ip * 3 if the most significant byte of the network number is greater than or equal to 240, then .i bits is 32. .ip * 3 otherwise, if the most significant byte of the network number is greater than or equal to 224, then .i bits is 4. .ip * 3 otherwise, if the most significant byte of the network number is greater than or equal to 192, then .i bits is 24. .ip * 3 otherwise, if the most significant byte of the network number is greater than or equal to 128, then .i bits is 16. .ip * otherwise, .i bits is 8. .pp if the resulting .i bits value from the above steps is greater than or equal to 8, but the number of octets specified in the network number exceed .ir "bits/8" , then .i bits is set to 8 times the number of octets actually specified. .sh examples the program below demonstrates the use of .br inet_net_pton () and .br inet_net_ntop (). it uses .br inet_net_pton () to convert the presentation format network address provided in its first command-line argument to binary form, displays the return value from .br inet_net_pton (). it then uses .br inet_net_ntop () to convert the binary form back to presentation format, and displays the resulting string. .pp in order to demonstrate that .br inet_net_pton () may not write to all bytes of its .i netp argument, the program allows an optional second command-line argument, a number used to initialize the buffer before .br inet_net_pton () is called. as its final line of output, the program displays all of the bytes of the buffer returned by .br inet_net_pton () allowing the user to see which bytes have not been touched by .br inet_net_pton (). .pp an example run, showing that .br inet_net_pton () infers the number of bits in the network number: .pp .in +4n .ex $ \fb./a.out 193.168\fp inet_net_pton() returned: 24 inet_net_ntop() yielded: 193.168.0/24 raw address: c1a80000 .ee .in .pp demonstrate that .br inet_net_pton () does not zero out unused bytes in its result buffer: .pp .in +4n .ex $ \fb./a.out 193.168 0xffffffff\fp inet_net_pton() returned: 24 inet_net_ntop() yielded: 193.168.0/24 raw address: c1a800ff .ee .in .pp demonstrate that .br inet_net_pton () will widen the inferred size of the network number, if the supplied number of bytes in the presentation string exceeds the inferred value: .pp .in +4n .ex $ \fb./a.out 193.168.1.128\fp inet_net_pton() returned: 32 inet_net_ntop() yielded: 193.168.1.128/32 raw address: c1a80180 .ee .in .pp explicitly specifying the size of the network number overrides any inference about its size (but any extra bytes that are explicitly specified will still be used by .br inet_net_pton (): to populate the result buffer): .pp .in +4n .ex $ \fb./a.out 193.168.1.128/24\fp inet_net_pton() returned: 24 inet_net_ntop() yielded: 193.168.1/24 raw address: c1a80180 .ee .in .ss program source .ex /* link with "\-lresolv" */ #include #include #include #define errexit(msg) do { perror(msg); exit(exit_failure); \e } while (0) int main(int argc, char *argv[]) { char buf[100]; struct in_addr addr; int bits; if (argc < 2) { fprintf(stderr, "usage: %s presentation\-form [addr\-init\-value]\en", argv[0]); exit(exit_failure); } /* if argv[2] is supplied (a numeric value), use it to initialize the output buffer given to inet_net_pton(), so that we can see that inet_net_pton() initializes only those bytes needed for the network number. if argv[2] is not supplied, then initialize the buffer to zero (as is recommended practice). */ addr.s_addr = (argc > 2) ? strtod(argv[2], null) : 0; /* convert presentation network number in argv[1] to binary. */ bits = inet_net_pton(af_inet, argv[1], &addr, sizeof(addr)); if (bits == \-1) errexit("inet_net_ntop"); printf("inet_net_pton() returned: %d\en", bits); /* convert binary format back to presentation, using \(aqbits\(aq returned by inet_net_pton(). */ if (inet_net_ntop(af_inet, &addr, bits, buf, sizeof(buf)) == null) errexit("inet_net_ntop"); printf("inet_net_ntop() yielded: %s\en", buf); /* display \(aqaddr\(aq in raw form (in network byte order), so we can see bytes not displayed by inet_net_ntop(); some of those bytes may not have been touched by inet_net_ntop(), and so will still have any initial value that was specified in argv[2]. */ printf("raw address: %x\en", htonl(addr.s_addr)); exit(exit_success); } .ee .sh see also .br inet (3), .br networks (5) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) andreas gruenbacher, february 2001 .\" copyright (c) silicon graphics inc, september 2001 .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .th getxattr 2 2021-03-22 "linux" "linux programmer's manual" .sh name getxattr, lgetxattr, fgetxattr \- retrieve an extended attribute value .sh synopsis .fam c .nf .b #include .pp .bi "ssize_t getxattr(const char *" path ", const char *" name , .bi " void *" value ", size_t " size ); .bi "ssize_t lgetxattr(const char *" path ", const char *" name , .bi " void *" value ", size_t " size ); .bi "ssize_t fgetxattr(int " fd ", const char *" name , .bi " void *" value ", size_t " size ); .fi .fam t .sh description extended attributes are .ir name :\c .i value pairs associated with inodes (files, directories, symbolic links, etc.). they are extensions to the normal attributes which are associated with all inodes in the system (i.e., the .br stat (2) data). a complete overview of extended attributes concepts can be found in .br xattr (7). .pp .br getxattr () retrieves the value of the extended attribute identified by .i name and associated with the given .i path in the filesystem. the attribute value is placed in the buffer pointed to by .ir value ; .i size specifies the size of that buffer. the return value of the call is the number of bytes placed in .ir value . .pp .br lgetxattr () is identical to .br getxattr (), except in the case of a symbolic link, where the link itself is interrogated, not the file that it refers to. .pp .br fgetxattr () is identical to .br getxattr (), only the open file referred to by .i fd (as returned by .br open (2)) is interrogated in place of .ir path . .pp an extended attribute .i name is a null-terminated string. the name includes a namespace prefix; there may be several, disjoint namespaces associated with an individual inode. the value of an extended attribute is a chunk of arbitrary textual or binary data that was assigned using .br setxattr (2). .pp if .i size is specified as zero, these calls return the current size of the named extended attribute (and leave .i value unchanged). this can be used to determine the size of the buffer that should be supplied in a subsequent call. (but, bear in mind that there is a possibility that the attribute value may change between the two calls, so that it is still necessary to check the return status from the second call.) .sh return value on success, these calls return a nonnegative value which is the size (in bytes) of the extended attribute value. on failure, \-1 is returned and .i errno is set to indicate the error. .sh errors .tp .b e2big the size of the attribute value is larger than the maximum size allowed; the attribute cannot be retrieved. this can happen on filesystems that support very large attribute values such as nfsv4, for example. .tp .b enodata the named attribute does not exist, or the process has no access to this attribute. .\" .rb ( enoattr .\" is defined to be a synonym for .\" .br enodata .\" in .\" .ir .) .tp .b enotsup extended attributes are not supported by the filesystem, or are disabled. .tp .b erange the .i size of the .i value buffer is too small to hold the result. .pp in addition, the errors documented in .br stat (2) can also occur. .sh versions these system calls have been available on linux since kernel 2.4; glibc support is provided since version 2.3. .sh conforming to these system calls are linux-specific. .\" .sh authors .\" andreas gruenbacher, .\" .ri < a.gruenbacher@computer.org > .\" and the sgi xfs development team, .\" .ri < linux-xfs@oss.sgi.com >. .\" please send any bug reports or comments to these addresses. .sh examples see .br listxattr (2). .sh see also .br getfattr (1), .br setfattr (1), .br listxattr (2), .br open (2), .br removexattr (2), .br setxattr (2), .br stat (2), .br symlink (7), .br xattr (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2006 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th sem_post 3 2021-03-22 "linux" "linux programmer's manual" .sh name sem_post \- unlock a semaphore .sh synopsis .nf .b #include .pp .bi "int sem_post(sem_t *" sem ); .fi .pp link with \fi\-pthread\fp. .sh description .br sem_post () increments (unlocks) the semaphore pointed to by .ir sem . if the semaphore's value consequently becomes greater than zero, then another process or thread blocked in a .br sem_wait (3) call will be woken up and proceed to lock the semaphore. .sh return value .br sem_post () returns 0 on success; on error, the value of the semaphore is left unchanged, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b einval .i sem is not a valid semaphore. .tp .b eoverflow .\" added in posix.1-2008 tc1 (austin interpretation 213) the maximum allowable value for a semaphore would be exceeded. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br sem_post () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001. .sh notes .br sem_post () is async-signal-safe: it may be safely called within a signal handler. .sh examples see .br sem_wait (3) and .br shm_open (3). .sh see also .br sem_getvalue (3), .br sem_wait (3), .br sem_overview (7), .br signal\-safety (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/err.3 .so man7/uri.7 .so man3/bswap.3 .so man3/isalpha.3 .so man2/send.2 .\" copyright (c) 1993 michael haardt (michael@moria.de) .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .\" created 1993-04-02 by michael haardt (michael@moria.de) .\" modified 1993-07-24 by rik faith (faith@cs.unc.edu) .\" modified 1994-05-15 by daniel quinlan (quinlan@yggdrasil.com) .\" modified 1994-11-22 by daniel quinlan (quinlan@yggdrasil.com) .\" modified 1995-07-11 by daniel quinlan (quinlan@yggdrasil.com) .\" modified 1996-12-18 by michael haardt and aeb .\" modified 1999-05-31 by dimitri papadopoulos (dpo@club-internet.fr) .\" modified 1999-08-08 by michael haardt (michael@moria.de) .\" modified 2004-04-01 by aeb .\" .th ascii 7 2020-06-09 "linux" "linux programmer's manual" .sh name ascii \- ascii character set encoded in octal, decimal, and hexadecimal .sh description ascii is the american standard code for information interchange. it is a 7-bit code. many 8-bit codes (e.g., iso 8859-1) contain ascii as their lower half. the international counterpart of ascii is known as iso 646-irv. .pp the following table contains the 128 ascii characters. .pp c program \f(cw\(aq\ex\(aq\fp escapes are noted. .if t \{\ .ft cw \} .ts l l l l | l l l l. oct dec hex char oct dec hex char _ 000 0 00 nul \(aq\e0\(aq (null character) 100 64 40 @ 001 1 01 soh (start of heading) 101 65 41 a 002 2 02 stx (start of text) 102 66 42 b 003 3 03 etx (end of text) 103 67 43 c 004 4 04 eot (end of transmission) 104 68 44 d 005 5 05 enq (enquiry) 105 69 45 e 006 6 06 ack (acknowledge) 106 70 46 f 007 7 07 bel \(aq\ea\(aq (bell) 107 71 47 g 010 8 08 bs \(aq\eb\(aq (backspace) 110 72 48 h 011 9 09 ht \(aq\et\(aq (horizontal tab) 111 73 49 i 012 10 0a lf \(aq\en\(aq (new line) 112 74 4a j 013 11 0b vt \(aq\ev\(aq (vertical tab) 113 75 4b k 014 12 0c ff \(aq\ef\(aq (form feed) 114 76 4c l 015 13 0d cr \(aq\er\(aq (carriage ret) 115 77 4d m 016 14 0e so (shift out) 116 78 4e n 017 15 0f si (shift in) 117 79 4f o 020 16 10 dle (data link escape) 120 80 50 p 021 17 11 dc1 (device control 1) 121 81 51 q 022 18 12 dc2 (device control 2) 122 82 52 r 023 19 13 dc3 (device control 3) 123 83 53 s 024 20 14 dc4 (device control 4) 124 84 54 t 025 21 15 nak (negative ack.) 125 85 55 u 026 22 16 syn (synchronous idle) 126 86 56 v 027 23 17 etb (end of trans. blk) 127 87 57 w 030 24 18 can (cancel) 130 88 58 x 031 25 19 em (end of medium) 131 89 59 y 032 26 1a sub (substitute) 132 90 5a z 033 27 1b esc (escape) 133 91 5b [ 034 28 1c fs (file separator) 134 92 5c \e \(aq\e\e\(aq 035 29 1d gs (group separator) 135 93 5d ] 036 30 1e rs (record separator) 136 94 5e \(ha 037 31 1f us (unit separator) 137 95 5f \&_ 040 32 20 space 140 96 60 \` 041 33 21 ! 141 97 61 a 042 34 22 " 142 98 62 b 043 35 23 # 143 99 63 c 044 36 24 $ 144 100 64 d 045 37 25 % 145 101 65 e 046 38 26 & 146 102 66 f 047 39 27 \(aq 147 103 67 g 050 40 28 ( 150 104 68 h 051 41 29 ) 151 105 69 i 052 42 2a * 152 106 6a j 053 43 2b + 153 107 6b k 054 44 2c , 154 108 6c l 055 45 2d \- 155 109 6d m 056 46 2e . 156 110 6e n 057 47 2f / 157 111 6f o 060 48 30 0 160 112 70 p 061 49 31 1 161 113 71 q 062 50 32 2 162 114 72 r 063 51 33 3 163 115 73 s 064 52 34 4 164 116 74 t 065 53 35 5 165 117 75 u 066 54 36 6 166 118 76 v 067 55 37 7 167 119 77 w 070 56 38 8 170 120 78 x 071 57 39 9 171 121 79 y 072 58 3a : 172 122 7a z 073 59 3b ; 173 123 7b { 074 60 3c < 174 124 7c | 075 61 3d = 175 125 7d } 076 62 3e > 176 126 7e \(ti 077 63 3f ? 177 127 7f del .te .if t \{\ .in .ft p \} .ss tables for convenience, below are more compact tables in hex and decimal. .pp .nf .if t \{\ .in 1i .ft cw \} 2 3 4 5 6 7 30 40 50 60 70 80 90 100 110 120 ------------- --------------------------------- 0: 0 @ p \` p 0: ( 2 < f p z d n x 1: ! 1 a q a q 1: ) 3 = g q [ e o y 2: " 2 b r b r 2: * 4 > h r \e f p z 3: # 3 c s c s 3: ! + 5 ? i s ] g q { 4: $ 4 d t d t 4: " , 6 @ j t \(ha h r | 5: % 5 e u e u 5: # \- 7 a k u _ i s } 6: & 6 f v f v 6: $ . 8 b l v \` j t \(ti 7: \(aq 7 g w g w 7: % / 9 c m w a k u del 8: ( 8 h x h x 8: & 0 : d n x b l v 9: ) 9 i y i y 9: \(aq 1 ; e o y c m w a: * : j z j z b: + ; k [ k { c: , < l \e l | d: \- = m ] m } e: . > n \(ha n \(ti f: / ? o _ o del .if t \{\ .in .ft p \} .fi .sh notes .ss history an .b ascii manual page appeared in version 7 of at&t unix. .pp on older terminals, the underscore code is displayed as a left arrow, called backarrow, the caret is displayed as an up-arrow and the vertical bar has a hole in the middle. .pp uppercase and lowercase characters differ by just one bit and the ascii character 2 differs from the double quote by just one bit, too. that made it much easier to encode characters mechanically or with a non-microcontroller-based electronic keyboard and that pairing was found on old teletypes. .pp the ascii standard was published by the united states of america standards institute (usasi) in 1968. .\" .\" asa was the american standards association and x3 was an asa sectional .\" committee on computers and data processing. its name changed to .\" american national standards committee x3 (ansc-x3) and now it is known .\" as accredited standards committee x3 (asc x3). it is accredited by ansi .\" and administered by iti. the subcommittee x3.2 worked on coded .\" character sets; the task group working on ascii appears to have been .\" designated x3.2.4. in 1966, asa became the united states of america .\" standards institute (usasi) and published ascii in 1968. it became the .\" american national standards institute (ansi) in 1969 and is the .\" u.s. member body of iso; private and nonprofit. .\" .sh see also .br charsets (7), .br iso_8859\-1 (7), .br iso_8859\-2 (7), .br iso_8859\-3 (7), .br iso_8859\-4 (7), .br iso_8859\-5 (7), .br iso_8859\-6 (7), .br iso_8859\-7 (7), .br iso_8859\-8 (7), .br iso_8859\-9 (7), .br iso_8859\-10 (7), .br iso_8859\-11 (7), .br iso_8859\-13 (7), .br iso_8859\-14 (7), .br iso_8859\-15 (7), .br iso_8859\-16 (7), .br utf\-8 (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/ctime.3 .\" copyright (c) 1992 drew eckhardt (drew@cs.colorado.edu), march 28, 1992 .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified by michael haardt .\" modified by thomas koenig .\" modified 1993-07-23 by rik faith .\" modified 1993-07-25 by rik faith .\" modified 1995-11-01 by michael haardt .\" .\" modified 1996-04-14 by andries brouwer .\" [added some polishing contributed by mike battersby ] .\" modified 1996-07-21 by andries brouwer .\" modified 1997-01-17 by andries brouwer .\" modified 2001-12-18 by andries brouwer .\" modified 2002-07-24 by michael kerrisk .\" added note on historical rules enforced when an unprivileged process .\" sends a signal. .\" modified 2004-06-16 by michael kerrisk .\" added note on cap_kill .\" modified 2004-06-24 by aeb .\" modified, 2004-11-30, after idea from emmanuel.colbus@ensimag.imag.fr .\" .th kill 2 2021-03-22 "linux" "linux programmer's manual" .sh name kill \- send signal to a process .sh synopsis .nf .b #include .pp .bi "int kill(pid_t " pid ", int " sig ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br kill (): .nf _posix_c_source .fi .sh description the .br kill () system call can be used to send any signal to any process group or process. .pp if \fipid\fp is positive, then signal \fisig\fp is sent to the process with the id specified by \fipid\fp. .pp if \fipid\fp equals 0, then \fisig\fp is sent to every process in the process group of the calling process. .pp if \fipid\fp equals \-1, then \fisig\fp is sent to every process for which the calling process has permission to send signals, except for process 1 (\fiinit\fp), but see below. .pp if \fipid\fp is less than \-1, then \fisig\fp is sent to every process in the process group whose id is \fi\-pid\fp. .pp if \fisig\fp is 0, then no signal is sent, but existence and permission checks are still performed; this can be used to check for the existence of a process id or process group id that the caller is permitted to signal. .pp for a process to have permission to send a signal, it must either be privileged (under linux: have the .b cap_kill capability in the user namespace of the target process), or the real or effective user id of the sending process must equal the real or saved set-user-id of the target process. in the case of .br sigcont , it suffices when the sending and receiving processes belong to the same session. (historically, the rules were different; see notes.) .sh return value on success (at least one signal was sent), zero is returned. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b einval an invalid signal was specified. .tp .b eperm the calling process does not have permission to send the signal to any of the target processes. .tp .b esrch the target process or process group does not exist. note that an existing process might be a zombie, a process that has terminated execution, but has not yet been .br wait (2)ed for. .sh conforming to posix.1-2001, posix.1-2008, svr4, 4.3bsd. .sh notes the only signals that can be sent to process id 1, the .i init process, are those for which .i init has explicitly installed signal handlers. this is done to assure the system is not brought down accidentally. .pp posix.1 requires that \fikill(\-1,sig)\fp send \fisig\fp to all processes that the calling process may send signals to, except possibly for some implementation-defined system processes. linux allows a process to signal itself, but on linux the call \fikill(\-1,sig)\fp does not signal the calling process. .pp posix.1 requires that if a process sends a signal to itself, and the sending thread does not have the signal blocked, and no other thread has it unblocked or is waiting for it in .br sigwait (3), at least one unblocked signal must be delivered to the sending thread before the .br kill () returns. .ss linux notes across different kernel versions, linux has enforced different rules for the permissions required for an unprivileged process to send a signal to another process. .\" in the 0.* kernels things chopped and changed quite .\" a bit - mtk, 24 jul 02 in kernels 1.0 to 1.2.2, a signal could be sent if the effective user id of the sender matched effective user id of the target, or the real user id of the sender matched the real user id of the target. from kernel 1.2.3 until 1.3.77, a signal could be sent if the effective user id of the sender matched either the real or effective user id of the target. the current rules, which conform to posix.1, were adopted in kernel 1.3.78. .sh bugs in 2.6 kernels up to and including 2.6.7, there was a bug that meant that when sending signals to a process group, .br kill () failed with the error .b eperm if the caller did not have permission to send the signal to \fiany\fp (rather than \fiall\fp) of the members of the process group. notwithstanding this error return, the signal was still delivered to all of the processes for which the caller had permission to signal. .sh see also .br kill (1), .br _exit (2), .br pidfd_send_signal (2), .br signal (2), .br tkill (2), .br exit (3), .br killpg (3), .br sigqueue (3), .br capabilities (7), .br credentials (7), .br signal (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sat jul 24 21:29:05 1993 by rik faith (faith@cs.unc.edu) .\" modified thu jul 26 14:06:20 2001 by andries brouwer (aeb@cwi.nl) .\" .th byteorder 3 2021-03-22 "gnu" "linux programmer's manual" .sh name htonl, htons, ntohl, ntohs \- convert values between host and network byte order .sh synopsis .nf .b #include .pp .bi "uint32_t htonl(uint32_t " hostlong ); .bi "uint16_t htons(uint16_t " hostshort ); .pp .bi "uint32_t ntohl(uint32_t " netlong ); .bi "uint16_t ntohs(uint16_t " netshort ); .fi .sh description the .br htonl () function converts the unsigned integer .i hostlong from host byte order to network byte order. .pp the .br htons () function converts the unsigned short integer .i hostshort from host byte order to network byte order. .pp the .br ntohl () function converts the unsigned integer .i netlong from network byte order to host byte order. .pp the .br ntohs () function converts the unsigned short integer .i netshort from network byte order to host byte order. .pp on the i386 the host byte order is least significant byte first, whereas the network byte order, as used on the internet, is most significant byte first. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br htonl (), .br htons (), .br ntohl (), .br ntohs () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .pp some systems require the inclusion of .i instead of .ir . .sh see also .br bswap (3), .br endian (3), .br gethostbyname (3), .br getservent (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) bruno haible .\" and copyright 2014 michael kerrisk .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th mbstowcs 3 2021-03-22 "gnu" "linux programmer's manual" .sh name mbstowcs \- convert a multibyte string to a wide-character string .sh synopsis .nf .b #include .pp .bi "size_t mbstowcs(wchar_t *restrict " dest ", const char *restrict " src , .bi " size_t " n ); .fi .sh description if .i dest is not null, the .br mbstowcs () function converts the multibyte string .i src to a wide-character string starting at .ir dest . at most .i n wide characters are written to .ir dest . the sequence of characters in the string .i src shall begin in the initial shift state. the conversion can stop for three reasons: .ip 1. 3 an invalid multibyte sequence has been encountered. in this case, .i (size_t)\ \-1 is returned. .ip 2. .i n non-l\(aq\e0\(aq wide characters have been stored at .ir dest . in this case, the number of wide characters written to .i dest is returned, but the shift state at this point is lost. .ip 3. the multibyte string has been completely converted, including the terminating null character (\(aq\e0\(aq). in this case, the number of wide characters written to .ir dest , excluding the terminating null wide character, is returned. .pp the programmer must ensure that there is room for at least .i n wide characters at .ir dest . .pp if .ir dest is null, .i n is ignored, and the conversion proceeds as above, except that the converted wide characters are not written out to memory, and that no length limit exists. .pp in order to avoid the case 2 above, the programmer should make sure .i n is greater than or equal to .ir "mbstowcs(null,src,0)+1" . .sh return value the .br mbstowcs () function returns the number of wide characters that make up the converted part of the wide-character string, not including the terminating null wide character. if an invalid multibyte sequence was encountered, .i (size_t)\ \-1 is returned. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br mbstowcs () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh notes the behavior of .br mbstowcs () depends on the .b lc_ctype category of the current locale. .pp the function .br mbsrtowcs (3) provides a better interface to the same functionality. .sh examples the program below illustrates the use of .br mbstowcs (), as well as some of the wide character classification functions. an example run is the following: .pp .in +4n .ex $ ./t_mbstowcs de_de.utf\-8 grüße! length of source string (excluding terminator): 8 bytes 6 multibyte characters wide character string is: grüße! (6 characters) g alpha upper r alpha lower ü alpha lower ß alpha lower e alpha lower ! !alpha .ee .in .ss program source \& .ex #include #include #include #include #include #include int main(int argc, char *argv[]) { size_t mbslen; /* number of multibyte characters in source */ wchar_t *wcs; /* pointer to converted wide character string */ if (argc < 3) { fprintf(stderr, "usage: %s \en", argv[0]); exit(exit_failure); } /* apply the specified locale. */ if (setlocale(lc_all, argv[1]) == null) { perror("setlocale"); exit(exit_failure); } /* calculate the length required to hold argv[2] converted to a wide character string. */ mbslen = mbstowcs(null, argv[2], 0); if (mbslen == (size_t) \-1) { perror("mbstowcs"); exit(exit_failure); } /* describe the source string to the user. */ printf("length of source string (excluding terminator):\en"); printf(" %zu bytes\en", strlen(argv[2])); printf(" %zu multibyte characters\en\en", mbslen); /* allocate wide character string of the desired size. add 1 to allow for terminating null wide character (l\(aq\e0\(aq). */ wcs = calloc(mbslen + 1, sizeof(*wcs)); if (wcs == null) { perror("calloc"); exit(exit_failure); } /* convert the multibyte character string in argv[2] to a wide character string. */ if (mbstowcs(wcs, argv[2], mbslen + 1) == (size_t) \-1) { perror("mbstowcs"); exit(exit_failure); } printf("wide character string is: %ls (%zu characters)\en", wcs, mbslen); /* now do some inspection of the classes of the characters in the wide character string. */ for (wchar_t *wp = wcs; *wp != 0; wp++) { printf(" %lc ", (wint_t) *wp); if (!iswalpha(*wp)) printf("!"); printf("alpha "); if (iswalpha(*wp)) { if (iswupper(*wp)) printf("upper "); if (iswlower(*wp)) printf("lower "); } putchar(\(aq\en\(aq); } exit(exit_success); } .ee .sh see also .br mblen (3), .br mbsrtowcs (3), .br mbtowc (3), .br wcstombs (3), .br wctomb (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/outb.2 .\" copyright (c) 2003 andries brouwer (aeb@cwi.nl) .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .th posixoptions 7 2021-08-27 "" "linux programmer's manual" .sh name posixoptions \- optional parts of the posix standard .sh description the posix standard (the information below is from posix.1-2001) describes a set of behaviors and interfaces for a compliant system. however, many interfaces are optional and there are feature test macros to test the availability of interfaces at compile time, and functions .br sysconf (3), .br fpathconf (3), .br pathconf (3), .br confstr (3) to do this at run time. from shell scripts one can use .br getconf (1). for more detail, see .br sysconf (3). .pp we give the name of the posix abbreviation, the option, the name of the .br sysconf (3) parameter used to inquire about the option, and possibly a very short description. much more precise detail can be found in the posix standard itself, versions of which can nowadays be accessed freely on the web. .ss adv - _posix_advisory_info - _sc_advisory_info the following advisory functions are present: .pp .nf .in +4n .ir posix_fadvise () .ir posix_fallocate () .ir posix_memalign () .ir posix_madvise () .in .fi .ss aio - _posix_asynchronous_io - _sc_asynchronous_io the header .i is present. the following functions are present: .pp .nf .in +4n .ir aio_cancel () .ir aio_error () .ir aio_fsync () .ir aio_read () .ir aio_return () .ir aio_suspend () .ir aio_write () .ir lio_listio () .in .fi .ss bar - _posix_barriers - _sc_barriers this option implies the .b _posix_threads and .b _posix_thread_safe_functions options. the following functions are present: .pp .nf .in +4n .ir pthread_barrier_destroy () .ir pthread_barrier_init () .ir pthread_barrier_wait () .ir pthread_barrierattr_destroy () .ir pthread_barrierattr_init () .in .fi .\" .ss be .\" batch environment. .\" .ss cd .\" c development. .ss --- - posix_chown_restricted if this option is in effect (as it always is under posix.1-2001), then only root may change the owner of a file, and nonroot can set the group of a file only to one of the groups it belongs to. this affects the following functions .pp .nf .in +4n .ir chown () .ir fchown () .in .fi .\" what about lchown() ? .ss cs - _posix_clock_selection - _sc_clock_selection this option implies the .b _posix_timers option. the following functions are present: .pp .nf .in +4n .ir pthread_condattr_getclock () .ir pthread_condattr_setclock () .ir clock_nanosleep () .in .fi .pp if .b clock_realtime is changed by the function .ir clock_settime (), then this affects all timers set for an absolute time. .ss cpt - _posix_cputime - _sc_cputime the .b clock_process_cputime_id clock id is supported. the initial value of this clock is 0 for each process. this option implies the .b _posix_timers option. the function .ir clock_getcpuclockid () is present. .\" .ss fd .\" fortran development .\" .ss fr .\" fortran runtime .ss --- - _posix_file_locking - _sc_file_locking this option has been deleted. not in final xpg6. .ss fsc - _posix_fsync - _sc_fsync the function .ir fsync () is present. .ss ip6 - _posix_ipv6 - _sc_ipv6 internet protocol version 6 is supported. .ss --- - _posix_job_control - _sc_job_control if this option is in effect (as it always is under posix.1-2001), then the system implements posix-style job control, and the following functions are present: .pp .nf .in +4n .ir setpgid () .ir tcdrain () .ir tcflush () .ir tcgetpgrp () .ir tcsendbreak () .ir tcsetattr () .ir tcsetpgrp () .in .fi .ss mf - _posix_mapped_files - _sc_mapped_files shared memory is supported. the include file .i is present. the following functions are present: .pp .nf .in +4n .ir mmap () .ir msync () .ir munmap () .in .fi .ss ml - _posix_memlock - _sc_memlock shared memory can be locked into core. the following functions are present: .pp .nf .in +4n .ir mlockall () .ir munlockall () .in .fi .ss mr/mlr - _posix_memlock_range - _sc_memlock_range more precisely, ranges can be locked into core. the following functions are present: .pp .nf .in +4n .ir mlock () .ir munlock () .in .fi .ss mpr - _posix_memory_protection - _sc_memory_protection the function .ir mprotect () is present. .ss msg - _posix_message_passing - _sc_message_passing the include file .i is present. the following functions are present: .pp .nf .in +4n .ir mq_close () .ir mq_getattr () .ir mq_notify () .ir mq_open () .ir mq_receive () .ir mq_send () .ir mq_setattr () .ir mq_unlink () .in .fi .ss mon - _posix_monotonic_clock - _sc_monotonic_clock .b clock_monotonic is supported. this option implies the .b _posix_timers option. the following functions are affected: .pp .nf .in +4n .ir aio_suspend () .ir clock_getres () .ir clock_gettime () .ir clock_settime () .ir timer_create () .in .fi .ss --- - _posix_multi_process - _sc_multi_process this option has been deleted. not in final xpg6. .\" .ss mx .\" iec 60559 floating-point option. .ss --- - _posix_no_trunc if this option is in effect (as it always is under posix.1-2001), then pathname components longer than .b name_max are not truncated, but give an error. this property may be dependent on the path prefix of the component. .ss pio - _posix_prioritized_io - _sc_prioritized_io this option says that one can specify priorities for asynchronous i/o. this affects the functions .pp .nf .in +4n .ir aio_read () .ir aio_write () .in .fi .ss ps - _posix_priority_scheduling - _sc_priority_scheduling the include file .i is present. the following functions are present: .pp .nf .in +4n .ir sched_get_priority_max () .ir sched_get_priority_min () .ir sched_getparam () .ir sched_getscheduler () .ir sched_rr_get_interval () .ir sched_setparam () .ir sched_setscheduler () .ir sched_yield () .in .fi .pp if also .b _posix_spawn is in effect, then the following functions are present: .pp .nf .in +4n .ir posix_spawnattr_getschedparam () .ir posix_spawnattr_getschedpolicy () .ir posix_spawnattr_setschedparam () .ir posix_spawnattr_setschedpolicy () .in .fi .ss rs - _posix_raw_sockets raw sockets are supported. the following functions are affected: .pp .nf .in +4n .ir getsockopt () .ir setsockopt () .in .fi .ss --- - _posix_reader_writer_locks - _sc_reader_writer_locks this option implies the .b _posix_threads option. conversely, under posix.1-2001 the .b _posix_threads option implies this option. .pp the following functions are present: .pp .in +4n .nf .ir pthread_rwlock_destroy () .ir pthread_rwlock_init () .ir pthread_rwlock_rdlock () .ir pthread_rwlock_tryrdlock () .ir pthread_rwlock_trywrlock () .ir pthread_rwlock_unlock () .ir pthread_rwlock_wrlock () .ir pthread_rwlockattr_destroy () .ir pthread_rwlockattr_init () .in .fi .ss rts - _posix_realtime_signals - _sc_realtime_signals realtime signals are supported. the following functions are present: .pp .nf .in +4n .ir sigqueue () .ir sigtimedwait () .ir sigwaitinfo () .in .fi .ss --- - _posix_regexp - _sc_regexp if this option is in effect (as it always is under posix.1-2001), then posix regular expressions are supported and the following functions are present: .pp .nf .in +4n .ir regcomp () .ir regerror () .ir regexec () .ir regfree () .in .fi .ss --- - _posix_saved_ids - _sc_saved_ids if this option is in effect (as it always is under posix.1-2001), then a process has a saved set-user-id and a saved set-group-id. the following functions are affected: .pp .nf .in +4n .ir exec () .ir kill () .ir seteuid () .ir setegid () .ir setgid () .ir setuid () .in .fi .\" .ss sd .\" software development .ss sem - _posix_semaphores - _sc_semaphores the include file .i is present. the following functions are present: .pp .nf .in +4n .ir sem_close () .ir sem_destroy () .ir sem_getvalue () .ir sem_init () .ir sem_open () .ir sem_post () .ir sem_trywait () .ir sem_unlink () .ir sem_wait () .in .fi .ss shm - _posix_shared_memory_objects - _sc_shared_memory_objects the following functions are present: .pp .nf .in +4n .ir mmap () .ir munmap () .ir shm_open () .ir shm_unlink () .in .fi .ss --- - _posix_shell - _sc_shell if this option is in effect (as it always is under posix.1-2001), the function .ir system () is present. .ss spn - _posix_spawn - _sc_spawn this option describes support for process creation in a context where it is difficult or impossible to use .ir fork (), for example, because no mmu is present. .pp if .b _posix_spawn is in effect, then the include file .i and the following functions are present: .pp .nf .in +4n .ir posix_spawn () .ir posix_spawn_file_actions_addclose () .ir posix_spawn_file_actions_adddup2 () .ir posix_spawn_file_actions_addopen () .ir posix_spawn_file_actions_destroy () .ir posix_spawn_file_actions_init () .ir posix_spawnattr_destroy () .ir posix_spawnattr_getsigdefault () .ir posix_spawnattr_getflags () .ir posix_spawnattr_getpgroup () .ir posix_spawnattr_getsigmask () .ir posix_spawnattr_init () .ir posix_spawnattr_setsigdefault () .ir posix_spawnattr_setflags () .ir posix_spawnattr_setpgroup () .ir posix_spawnattr_setsigmask () .ir posix_spawnp () .in .fi .pp if also .b _posix_priority_scheduling is in effect, then the following functions are present: .pp .nf .in +4n .ir posix_spawnattr_getschedparam () .ir posix_spawnattr_getschedpolicy () .ir posix_spawnattr_setschedparam () .ir posix_spawnattr_setschedpolicy () .in .fi .ss spi - _posix_spin_locks - _sc_spin_locks this option implies the .b _posix_threads and .b _posix_thread_safe_functions options. the following functions are present: .pp .nf .in +4n .ir pthread_spin_destroy () .ir pthread_spin_init () .ir pthread_spin_lock () .ir pthread_spin_trylock () .ir pthread_spin_unlock () .in -4n .fi .ss ss - _posix_sporadic_server - _sc_sporadic_server the scheduling policy .b sched_sporadic is supported. this option implies the .b _posix_priority_scheduling option. the following functions are affected: .pp .nf .in +4n .ir sched_setparam () .ir sched_setscheduler () .in .fi .ss sio - _posix_synchronized_io - _sc_synchronized_io the following functions are affected: .pp .nf .in +4n .ir open () .ir msync () .ir fsync () .ir fdatasync () .in .fi .ss tsa - _posix_thread_attr_stackaddr - _sc_thread_attr_stackaddr the following functions are affected: .pp .nf .in +4n .ir pthread_attr_getstack () .ir pthread_attr_getstackaddr () .ir pthread_attr_setstack () .ir pthread_attr_setstackaddr () .in .fi .ss tss - _posix_thread_attr_stacksize - _sc_thread_attr_stacksize the following functions are affected: .pp .nf .in +4n .ir pthread_attr_getstack () .ir pthread_attr_getstacksize () .ir pthread_attr_setstack () .ir pthread_attr_setstacksize () .in .fi .ss tct - _posix_thread_cputime - _sc_thread_cputime the clockid clock_thread_cputime_id is supported. this option implies the .b _posix_timers option. the following functions are affected: .pp .nf .in +4n .ir pthread_getcpuclockid () .ir clock_getres () .ir clock_gettime () .ir clock_settime () .ir timer_create () .in .fi .ss tpi - _posix_thread_prio_inherit - _sc_thread_prio_inherit the following functions are affected: .pp .nf .in +4n .ir pthread_mutexattr_getprotocol () .ir pthread_mutexattr_setprotocol () .in .fi .ss tpp - _posix_thread_prio_protect - _sc_thread_prio_protect the following functions are affected: .pp .nf .in +4n .ir pthread_mutex_getprioceiling () .ir pthread_mutex_setprioceiling () .ir pthread_mutexattr_getprioceiling () .ir pthread_mutexattr_getprotocol () .ir pthread_mutexattr_setprioceiling () .ir pthread_mutexattr_setprotocol () .in .fi .ss tps - _posix_thread_priority_scheduling - _sc_thread_priority_scheduling if this option is in effect, the different threads inside a process can run with different priorities and/or different schedulers. the following functions are affected: .pp .nf .in +4n .ir pthread_attr_getinheritsched () .ir pthread_attr_getschedpolicy () .ir pthread_attr_getscope () .ir pthread_attr_setinheritsched () .ir pthread_attr_setschedpolicy () .ir pthread_attr_setscope () .ir pthread_getschedparam () .ir pthread_setschedparam () .ir pthread_setschedprio () .in .fi .ss tsh - _posix_thread_process_shared - _sc_thread_process_shared the following functions are affected: .pp .nf .in +4n .ir pthread_barrierattr_getpshared () .ir pthread_barrierattr_setpshared () .ir pthread_condattr_getpshared () .ir pthread_condattr_setpshared () .ir pthread_mutexattr_getpshared () .ir pthread_mutexattr_setpshared () .ir pthread_rwlockattr_getpshared () .ir pthread_rwlockattr_setpshared () .in .fi .ss tsf - _posix_thread_safe_functions - _sc_thread_safe_functions the following functions are affected: .pp .nf .in +4n .ir readdir_r () .ir getgrgid_r () .ir getgrnam_r () .ir getpwnam_r () .ir getpwuid_r () .ir flockfile () .ir ftrylockfile () .ir funlockfile () .ir getc_unlocked () .ir getchar_unlocked () .ir putc_unlocked () .ir putchar_unlocked () .ir rand_r () .ir strerror_r () .ir strtok_r () .ir asctime_r () .ir ctime_r () .ir gmtime_r () .ir localtime_r () .in .fi .ss tsp - _posix_thread_sporadic_server - _sc_thread_sporadic_server this option implies the .b _posix_thread_priority_scheduling option. the following functions are affected: .pp .nf .in +4n .ir sched_getparam () .ir sched_setparam () .ir sched_setscheduler () .in .fi .ss thr - _posix_threads - _sc_threads basic support for posix threads is available. the following functions are present: .pp .nf .in +4n .ir pthread_atfork () .ir pthread_attr_destroy () .ir pthread_attr_getdetachstate () .ir pthread_attr_getschedparam () .ir pthread_attr_init () .ir pthread_attr_setdetachstate () .ir pthread_attr_setschedparam () .ir pthread_cancel () .ir pthread_cleanup_push () .ir pthread_cleanup_pop () .ir pthread_cond_broadcast () .ir pthread_cond_destroy () .ir pthread_cond_init () .ir pthread_cond_signal () .ir pthread_cond_timedwait () .ir pthread_cond_wait () .ir pthread_condattr_destroy () .ir pthread_condattr_init () .ir pthread_create () .ir pthread_detach () .ir pthread_equal () .ir pthread_exit () .ir pthread_getspecific () .ir pthread_join () .ir pthread_key_create () .ir pthread_key_delete () .ir pthread_mutex_destroy () .ir pthread_mutex_init () .ir pthread_mutex_lock () .ir pthread_mutex_trylock () .ir pthread_mutex_unlock () .ir pthread_mutexattr_destroy () .ir pthread_mutexattr_init () .ir pthread_once () .ir pthread_rwlock_destroy () .ir pthread_rwlock_init () .ir pthread_rwlock_rdlock () .ir pthread_rwlock_tryrdlock () .ir pthread_rwlock_trywrlock () .ir pthread_rwlock_unlock () .ir pthread_rwlock_wrlock () .ir pthread_rwlockattr_destroy () .ir pthread_rwlockattr_init () .ir pthread_self () .ir pthread_setcancelstate () .ir pthread_setcanceltype () .ir pthread_setspecific () .ir pthread_testcancel () .in .fi .ss tmo - _posix_timeouts - _sc_timeouts the following functions are present: .pp .nf .in +4n .ir mq_timedreceive () .ir mq_timedsend () .ir pthread_mutex_timedlock () .ir pthread_rwlock_timedrdlock () .ir pthread_rwlock_timedwrlock () .ir sem_timedwait () .ir posix_trace_timedgetnext_event () .in .fi .ss tmr - _posix_timers - _sc_timers the following functions are present: .pp .nf .in +4n .ir clock_getres () .ir clock_gettime () .ir clock_settime () .ir nanosleep () .ir timer_create () .ir timer_delete () .ir timer_gettime () .ir timer_getoverrun () .ir timer_settime () .in .fi .ss trc - _posix_trace - _sc_trace posix tracing is available. the following functions are present: .pp .nf .in +4n .ir posix_trace_attr_destroy () .ir posix_trace_attr_getclockres () .ir posix_trace_attr_getcreatetime () .ir posix_trace_attr_getgenversion () .ir posix_trace_attr_getmaxdatasize () .ir posix_trace_attr_getmaxsystemeventsize () .ir posix_trace_attr_getmaxusereventsize () .ir posix_trace_attr_getname () .ir posix_trace_attr_getstreamfullpolicy () .ir posix_trace_attr_getstreamsize () .ir posix_trace_attr_init () .ir posix_trace_attr_setmaxdatasize () .ir posix_trace_attr_setname () .ir posix_trace_attr_setstreamsize () .ir posix_trace_attr_setstreamfullpolicy () .ir posix_trace_clear () .ir posix_trace_create () .ir posix_trace_event () .ir posix_trace_eventid_equal () .ir posix_trace_eventid_get_name () .ir posix_trace_eventid_open () .ir posix_trace_eventtypelist_getnext_id () .ir posix_trace_eventtypelist_rewind () .ir posix_trace_flush () .ir posix_trace_get_attr () .ir posix_trace_get_status () .ir posix_trace_getnext_event () .ir posix_trace_shutdown () .ir posix_trace_start () .ir posix_trace_stop () .ir posix_trace_trygetnext_event () .in .fi .ss tef - _posix_trace_event_filter - _sc_trace_event_filter this option implies the .b _posix_trace option. the following functions are present: .pp .nf .in +4n .ir posix_trace_eventset_add () .ir posix_trace_eventset_del () .ir posix_trace_eventset_empty () .ir posix_trace_eventset_fill () .ir posix_trace_eventset_ismember () .ir posix_trace_get_filter () .ir posix_trace_set_filter () .ir posix_trace_trid_eventid_open () .in .fi .ss tri - _posix_trace_inherit - _sc_trace_inherit tracing children of the traced process is supported. this option implies the .b _posix_trace option. the following functions are present: .pp .nf .in +4n .ir posix_trace_attr_getinherited () .ir posix_trace_attr_setinherited () .in .fi .ss trl - _posix_trace_log - _sc_trace_log this option implies the .b _posix_trace option. the following functions are present: .pp .nf .in +4n .ir posix_trace_attr_getlogfullpolicy () .ir posix_trace_attr_getlogsize () .ir posix_trace_attr_setlogfullpolicy () .ir posix_trace_attr_setlogsize () .ir posix_trace_close () .ir posix_trace_create_withlog () .ir posix_trace_open () .ir posix_trace_rewind () .in .fi .ss tym - _posix_typed_memory_objects - _sc_typed_memory_object the following functions are present: .pp .nf .in +4n .ir posix_mem_offset () .ir posix_typed_mem_get_info () .ir posix_typed_mem_open () .in .fi .ss --- - _posix_vdisable always present (probably 0). value to set a changeable special control character to indicate that it is disabled. .sh x/open system interface extensions .ss xsi - _xopen_crypt - _sc_xopen_crypt the following functions are present: .pp .nf .in +4n .ir crypt () .ir encrypt () .ir setkey () .fi .ss xsi - _xopen_realtime - _sc_xopen_realtime this option implies the following options: .pp .pd 0 .tp .br _posix_asynchronous_io == 200112l .tp .b _posix_fsync .tp .b _posix_mapped_files .tp .br _posix_memlock == 200112l .tp .br _posix_memlock_range == 200112l .tp .b _posix_memory_protection .tp .br _posix_message_passing == 200112l .tp .b _posix_prioritized_io .tp .br _posix_priority_scheduling == 200112l .tp .br _posix_realtime_signals == 200112l .tp .br _posix_semaphores == 200112l .tp .br _posix_shared_memory_objects == 200112l .tp .br _posix_synchronized_io == 200112l .tp .br _posix_timers == 200112l .pd .\" .ss adv - --- - --- the advanced realtime option group implies that the following options are all defined to 200112l: .pp .pd 0 .tp .b _posix_advisory_info .tp .b _posix_clock_selection (implies .br _posix_timers ) .tp .b _posix_cputime (implies .br _posix_timers ) .tp .b _posix_monotonic_clock (implies .br _posix_timers ) .tp .b _posix_spawn .tp .b _posix_sporadic_server (implies .br _posix_priority_scheduling ) .tp .b _posix_timeouts .tp .b _posix_typed_memory_objects .pd .\" .ss xsi - _xopen_realtime_threads - _sc_xopen_realtime_threads this option implies that the following options are all defined to 200112l: .pp .pd 0 .tp .b _posix_thread_prio_inherit .tp .b _posix_thread_prio_protect .tp .b _posix_thread_priority_scheduling .pd .ss advanced realtime threads - --- - --- this option implies that the following options are all defined to 200112l: .pp .pd 0 .tp .b _posix_barriers (implies .br _posix_threads , .br _posix_thread_safe_functions ) .tp .b _posix_spin_locks (implies .br _posix_threads , .br _posix_thread_safe_functions ) .tp .b _posix_thread_cputime (implies .br _posix_timers ) .tp .b _posix_thread_sporadic_server (implies .br _posix_thread_priority_scheduling ) .pd .\" .ss tracing - --- - --- this option implies that the following options are all defined to 200112l: .pp .pd 0 .tp .b _posix_trace .tp .b _posix_trace_event_filter .tp .b _posix_trace_log .tp .b _posix_trace_inherit .pd .ss streams - _xopen_streams - _sc_xopen_streams the following functions are present: .pp .nf .in +4n .ir fattach () .ir fdetach () .ir getmsg () .ir getpmsg () .ir ioctl () .ir isastream () .ir putmsg () .ir putpmsg () .in .fi .ss xsi - _xopen_legacy - _sc_xopen_legacy functions included in the legacy option group were previously mandatory, but are now optional in this version. the following functions are present: .pp .nf .in +4n .ir bcmp () .ir bcopy () .ir bzero () .ir ecvt () .ir fcvt () .ir ftime () .ir gcvt () .ir getwd () .ir index () .ir mktemp () .ir rindex () .ir utimes () .ir wcswcs () .in .fi .ss xsi - _xopen_unix - _sc_xopen_unix the following functions are present: .pp .nf .in +4n .ir mmap () .ir munmap () .ir msync () .in .fi .pp this option implies the following options: .pp .pd 0 .tp .b _posix_fsync .tp .b _posix_mapped_files .tp .b _posix_memory_protection .tp .b _posix_thread_attr_stackaddr .tp .b _posix_thread_attr_stacksize .tp .b _posix_thread_process_shared .tp .b _posix_thread_safe_functions .tp .b _posix_threads .pd .pp this option may imply the following options from the xsi option groups: .pp .pd 0 .tp .rb "encryption (" _xopen_crypt ) .tp .rb "realtime (" _xopen_realtime ) .tp .rb "advanced realtime (" adb ) .tp .rb "realtime threads (" _xopen_realtime_threads ) .tp .rb "advanced realtime threads (" "advanced realtime threads" ) .tp .rb "tracing (" tracing ) .tp .rb "xsi streams (" streams ) .tp .rb "legacy (" _xopen_legacy ) .pd .sh see also .br sysconf (3), .br standards (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 2009 intel corporation .\" author: andi kleen .\" based on the move_pages manpage which was .\" this manpage is copyright (c) 2006 silicon graphics, inc. .\" christoph lameter .\" .\" %%%license_start(verbatim_two_para) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" %%%license_end .\" .th migrate_pages 2 2021-03-22 "linux" "linux programmer's manual" .sh name migrate_pages \- move all pages in a process to another set of nodes .sh synopsis .nf .b #include .pp .bi "long migrate_pages(int " pid ", unsigned long " maxnode, .bi " const unsigned long *" old_nodes, .bi " const unsigned long *" new_nodes ); .fi .pp .ir note : there is no glibc wrapper for this system call; see notes. .pp link with \fi\-lnuma\fp. .sh description .br migrate_pages () attempts to move all pages of the process .i pid that are in memory nodes .i old_nodes to the memory nodes in .ir new_nodes . pages not located in any node in .i old_nodes will not be migrated. as far as possible, the kernel maintains the relative topology relationship inside .i old_nodes during the migration to .ir new_nodes . .pp the .i old_nodes and .i new_nodes arguments are pointers to bit masks of node numbers, with up to .i maxnode bits in each mask. these masks are maintained as arrays of unsigned .i long integers (in the last .i long integer, the bits beyond those specified by .i maxnode are ignored). the .i maxnode argument is the maximum node number in the bit mask plus one (this is the same as in .br mbind (2), but different from .br select (2)). .pp the .i pid argument is the id of the process whose pages are to be moved. to move pages in another process, the caller must be privileged .rb ( cap_sys_nice ) or the real or effective user id of the calling process must match the real or saved-set user id of the target process. if .i pid is 0, then .br migrate_pages () moves pages of the calling process. .pp pages shared with another process will be moved only if the initiating process has the .b cap_sys_nice privilege. .sh return value on success .br migrate_pages () returns the number of pages that could not be moved (i.e., a return of zero means that all pages were successfully moved). on error, it returns \-1, and sets .i errno to indicate the error. .sh errors .tp .b efault part or all of the memory range specified by .ir old_nodes / new_nodes and .i maxnode points outside your accessible address space. .tp .b einval the value specified by .i maxnode exceeds a kernel-imposed limit. .\" as at 3.5, this limit is "a page worth of bits", e.g., .\" 8 * 4096 bits, assuming a 4kb page size. or, .i old_nodes or .i new_nodes specifies one or more node ids that are greater than the maximum supported node id. or, none of the node ids specified by .i new_nodes are on-line and allowed by the process's current cpuset context, or none of the specified nodes contain memory. .tp .b eperm insufficient privilege .rb ( cap_sys_nice ) to move pages of the process specified by .ir pid , or insufficient privilege .rb ( cap_sys_nice ) to access the specified target nodes. .tp .b esrch no process matching .i pid could be found. .\" fixme document the other errors that can occur for migrate_pages() .sh versions the .br migrate_pages () system call first appeared on linux in version 2.6.16. .sh conforming to this system call is linux-specific. .sh notes glibc does not provide a wrapper for this system call. for information on library support, see .br numa (7). .pp use .br get_mempolicy (2) with the .b mpol_f_mems_allowed flag to obtain the set of nodes that are allowed by the calling process's cpuset. note that this information is subject to change at any time by manual or automatic reconfiguration of the cpuset. .pp use of .br migrate_pages () may result in pages whose location (node) violates the memory policy established for the specified addresses (see .br mbind (2)) and/or the specified process (see .br set_mempolicy (2)). that is, memory policy does not constrain the destination nodes used by .br migrate_pages (). .pp the .i header is not included with glibc, but requires installing .i libnuma\-devel or a similar package. .sh see also .br get_mempolicy (2), .br mbind (2), .br set_mempolicy (2), .br numa (3), .br numa_maps (5), .br cpuset (7), .br numa (7), .br migratepages (8), .br numastat (8) .pp .ir documentation/vm/page_migration.rst in the linux kernel source tree .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2006 by michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th fcloseall 3 2021-03-22 "gnu" "linux programmer's manual" .sh name fcloseall \- close all open streams .sh synopsis .nf .br "#define _gnu_source" " /* see feature_test_macros(7) */" .b #include .pp .b int fcloseall(void); .fi .sh description the .br fcloseall () function closes all of the calling process's open streams. buffered output for each stream is written before it is closed (as for .br fflush (3)); buffered input is discarded. .pp the standard streams, .ir stdin , .ir stdout , and .i stderr are also closed. .sh return value this function returns 0 if all files were successfully closed; on error, .b eof is returned. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br fcloseall () t} thread safety mt-unsafe race:streams .te .hy .ad .sp 1 .pp the .br fcloseall () function does not lock the streams, so it is not thread-safe. .sh conforming to this function is a gnu extension. .sh see also .br close (2), .br fclose (3), .br fflush (3), .br fopen (3), .br setbuf (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/lrint.3 .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th wcsrchr 3 2021-03-22 "gnu" "linux programmer's manual" .sh name wcsrchr \- search a wide character in a wide-character string .sh synopsis .nf .b #include .pp .bi "wchar_t *wcsrchr(const wchar_t *" wcs ", wchar_t " wc ); .fi .sh description the .br wcsrchr () function is the wide-character equivalent of the .br strrchr (3) function. it searches the last occurrence of .i wc in the wide-character string pointed to by .ir wcs . .sh return value the .br wcsrchr () function returns a pointer to the last occurrence of .i wc in the wide-character string pointed to by .ir wcs , or null if .i wc does not occur in the string. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br wcsrchr () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh see also .br strrchr (3), .br wcschr (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-9.7 .\" copyright (c) 2009 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_kill_other_threads_np 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_kill_other_threads_np \- terminate all other threads in process .sh synopsis .nf .b #include .pp .b void pthread_kill_other_threads_np(void); .fi .sh description .br pthread_kill_other_threads_np () has an effect only in the linuxthreads threading implementation. on that implementation, calling this function causes the immediate termination of all threads in the application, except the calling thread. the cancellation state and cancellation type of the to-be-terminated threads are ignored, and the cleanup handlers are not called in those threads. .\" .sh versions .\" available since glibc 2.0 .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_kill_other_threads_np () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to this function is a nonstandard gnu extension; hence the suffix "_np" (nonportable) in the name. .sh notes .br pthread_kill_other_threads_np () is intended to be called just before a thread calls .br execve (2) or a similar function. this function is designed to address a limitation in the obsolete linuxthreads implementation whereby the other threads of an application are not automatically terminated (as posix.1-2001 requires) during .br execve (2). .pp in the nptl threading implementation, .br pthread_kill_other_threads_np () exists, but does nothing. (nothing needs to be done, because the implementation does the right thing during an .br execve (2).) .sh see also .br execve (2), .br pthread_cancel (3), .br pthread_setcancelstate (3), .br pthread_setcanceltype (3), .br pthreads (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/infinity.3 .so man3/makedev.3 .so man7/system_data_types.7 .so man3/stailq.3 .so man3/y0.3 .so man3/termios.3 .so man3/posix_spawn.3 .so man3/byteorder.3 .\" copyright (c) 2008 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_self 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_self \- obtain id of the calling thread .sh synopsis .nf .b #include .pp .b pthread_t pthread_self(void); .pp compile and link with \fi\-pthread\fp. .fi .sh description the .br pthread_self () function returns the id of the calling thread. this is the same value that is returned in .ir *thread in the .br pthread_create (3) call that created this thread. .sh return value this function always succeeds, returning the calling thread's id. .sh errors this function always succeeds. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_self () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes posix.1 allows an implementation wide freedom in choosing the type used to represent a thread id; for example, representation using either an arithmetic type or a structure is permitted. therefore, variables of type .i pthread_t can't portably be compared using the c equality operator (\fb==\fp); use .br pthread_equal (3) instead. .pp thread identifiers should be considered opaque: any attempt to use a thread id other than in pthreads calls is nonportable and can lead to unspecified results. .pp thread ids are guaranteed to be unique only within a process. a thread id may be reused after a terminated thread has been joined, or a detached thread has terminated. .pp the thread id returned by .br pthread_self () is not the same thing as the kernel thread id returned by a call to .br gettid (2). .sh see also .br pthread_create (3), .br pthread_equal (3), .br pthreads (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/slist.3 .so man3/isalpha.3 .so man3/tanh.3 .so man3/envz_add.3 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sun jul 25 10:41:28 1993 by rik faith (faith@cs.unc.edu) .th strxfrm 3 2021-03-22 "gnu" "linux programmer's manual" .sh name strxfrm \- string transformation .sh synopsis .nf .b #include .pp .bi "size_t strxfrm(char *restrict " dest ", const char *restrict " src , .bi " size_t " n ); .fi .sh description the .br strxfrm () function transforms the .i src string into a form such that the result of .br strcmp (3) on two strings that have been transformed with .br strxfrm () is the same as the result of .br strcoll (3) on the two strings before their transformation. the first .i n bytes of the transformed string are placed in .ir dest . the transformation is based on the program's current locale for category .br lc_collate . (see .br setlocale (3)). .sh return value the .br strxfrm () function returns the number of bytes required to store the transformed string in .i dest excluding the terminating null byte (\(aq\e0\(aq). if the value returned is .i n or more, the contents of .i dest are indeterminate. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br strxfrm () t} thread safety mt-safe locale .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c89, c99, svr4, 4.3bsd. .sh see also .br bcmp (3), .br memcmp (3), .br setlocale (3), .br strcasecmp (3), .br strcmp (3), .br strcoll (3), .br string (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1993 michael haardt (michael@moria.de), .\" fri apr 2 11:32:09 met dst 1993 .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .\" modified sun jul 25 11:06:22 1993 by rik faith .\" modified mon oct 21 17:47:19 edt 1996 by eric s. raymond .th issue 5 1993-07-24 "linux" "linux programmer's manual" .sh name issue \- prelogin message and identification file .sh description .i /etc/issue is a text file which contains a message or system identification to be printed before the login prompt. it may contain various \fb@\fp\fichar\fp and \fb\e\fp\fichar\fp sequences, if supported by the .br getty -type program employed on the system. .sh files .i /etc/issue .sh see also .br motd (5), .br agetty (8), .br mingetty (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1992 drew eckhardt , march 28, 1992 .\" and copyright (c) michael kerrisk, 2001, 2002, 2005, 2013, 2019 .\" .\" %%%license_start(gpl_noversion_oneline) .\" may be distributed under the gnu general public license. .\" %%%license_end .\" .\" modified by michael haardt .\" modified 24 jul 1993 by rik faith .\" modified 21 aug 1994 by michael chastain : .\" new man page (copied from 'fork.2'). .\" modified 10 june 1995 by andries brouwer .\" modified 25 april 1998 by xavier leroy .\" modified 26 jun 2001 by michael kerrisk .\" mostly upgraded to 2.4.x .\" added prototype for sys_clone() plus description .\" added clone_thread with a brief description of thread groups .\" added clone_parent and revised entire page remove ambiguity .\" between "calling process" and "parent process" .\" added clone_ptrace and clone_vfork .\" added eperm and einval error codes .\" renamed "__clone" to "clone" (which is the prototype in ) .\" various other minor tidy ups and clarifications. .\" modified 26 jun 2001 by michael kerrisk .\" updated notes for 2.4.7+ behavior of clone_thread .\" modified 15 oct 2002 by michael kerrisk .\" added description for clone_newns, which was added in 2.4.19 .\" slightly rephrased, aeb. .\" modified 1 feb 2003 - added clone_sighand restriction, aeb. .\" modified 1 jan 2004 - various updates, aeb .\" modified 2004-09-10 - added clone_parent_settid etc. - aeb. .\" 2005-04-12, mtk, noted the pid caching behavior of nptl's getpid() .\" wrapper under bugs. .\" 2005-05-10, mtk, added clone_sysvsem, clone_untraced, clone_stopped. .\" 2005-05-17, mtk, substantially enhanced discussion of clone_thread. .\" 2008-11-18, mtk, order clone_* flags alphabetically .\" 2008-11-18, mtk, document clone_newpid .\" 2008-11-19, mtk, document clone_newuts .\" 2008-11-19, mtk, document clone_newipc .\" 2008-11-19, jens axboe, mtk, document clone_io .\" .th clone 2 2021-03-22 "linux" "linux programmer's manual" .sh name clone, __clone2, clone3 \- create a child process .sh synopsis .nf /* prototype for the glibc wrapper function */ .pp .b #define _gnu_source .b #include .pp .bi "int clone(int (*" "fn" ")(void *), void *" stack \ ", int " flags ", void *" "arg" ", ..." .bi " /* pid_t *" parent_tid ", void *" tls \ ", pid_t *" child_tid " */ );" .pp /* for the prototype of the raw clone() system call, see notes */ .pp .br "#include " " /* definition of " "struct clone_args" " */" .br "#include " " /* definition of " clone_* " constants */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "long syscall(sys_clone3, struct clone_args *" cl_args ", size_t " size ); .fi .pp .ir note : glibc provides no wrapper for .br clone3 (), necessitating the use of .br syscall (2). .sh description these system calls create a new ("child") process, in a manner similar to .br fork (2). .pp by contrast with .br fork (2), these system calls provide more precise control over what pieces of execution context are shared between the calling process and the child process. for example, using these system calls, the caller can control whether or not the two processes share the virtual address space, the table of file descriptors, and the table of signal handlers. these system calls also allow the new child process to be placed in separate .br namespaces (7). .pp note that in this manual page, "calling process" normally corresponds to "parent process". but see the descriptions of .b clone_parent and .b clone_thread below. .pp this page describes the following interfaces: .ip * 3 the glibc .br clone () wrapper function and the underlying system call on which it is based. the main text describes the wrapper function; the differences for the raw system call are described toward the end of this page. .ip * the newer .br clone3 () system call. .pp in the remainder of this page, the terminology "the clone call" is used when noting details that apply to all of these interfaces, .\" .ss the clone() wrapper function when the child process is created with the .br clone () wrapper function, it commences execution by calling the function pointed to by the argument .ir fn . (this differs from .br fork (2), where execution continues in the child from the point of the .br fork (2) call.) the .i arg argument is passed as the argument of the function .ir fn . .pp when the .ir fn ( arg ) function returns, the child process terminates. the integer returned by .i fn is the exit status for the child process. the child process may also terminate explicitly by calling .br exit (2) or after receiving a fatal signal. .pp the .i stack argument specifies the location of the stack used by the child process. since the child and calling process may share memory, it is not possible for the child process to execute in the same stack as the calling process. the calling process must therefore set up memory space for the child stack and pass a pointer to this space to .br clone (). stacks grow downward on all processors that run linux (except the hp pa processors), so .i stack usually points to the topmost address of the memory space set up for the child stack. note that .br clone () does not provide a means whereby the caller can inform the kernel of the size of the stack area. .pp the remaining arguments to .br clone () are discussed below. .\" .ss clone3() the .br clone3 () system call provides a superset of the functionality of the older .br clone () interface. it also provides a number of api improvements, including: space for additional flags bits; cleaner separation in the use of various arguments; and the ability to specify the size of the child's stack area. .pp as with .br fork (2), .br clone3 () returns in both the parent and the child. it returns 0 in the child process and returns the pid of the child in the parent. .pp the .i cl_args argument of .br clone3 () is a structure of the following form: .pp .in +4n .ex struct clone_args { u64 flags; /* flags bit mask */ u64 pidfd; /* where to store pid file descriptor (\fiint *\fp) */ u64 child_tid; /* where to store child tid, in child\(aqs memory (\fipid_t *\fp) */ u64 parent_tid; /* where to store child tid, in parent\(aqs memory (\fipid_t *\fp) */ u64 exit_signal; /* signal to deliver to parent on child termination */ u64 stack; /* pointer to lowest byte of stack */ u64 stack_size; /* size of stack */ u64 tls; /* location of new tls */ u64 set_tid; /* pointer to a \fipid_t\fp array (since linux 5.5) */ u64 set_tid_size; /* number of elements in \fiset_tid\fp (since linux 5.5) */ u64 cgroup; /* file descriptor for target cgroup of child (since linux 5.7) */ }; .ee .in .pp the .i size argument that is supplied to .br clone3 () should be initialized to the size of this structure. (the existence of the .i size argument permits future extensions to the .ir clone_args structure.) .pp the stack for the child process is specified via .ir cl_args.stack , which points to the lowest byte of the stack area, and .ir cl_args.stack_size , which specifies the size of the stack in bytes. in the case where the .br clone_vm flag (see below) is specified, a stack must be explicitly allocated and specified. otherwise, these two fields can be specified as null and 0, which causes the child to use the same stack area as the parent (in the child's own virtual address space). .pp the remaining fields in the .i cl_args argument are discussed below. .\" .ss equivalence between clone() and clone3() arguments unlike the older .br clone () interface, where arguments are passed individually, in the newer .br clone3 () interface the arguments are packaged into the .i clone_args structure shown above. this structure allows for a superset of the information passed via the .br clone () arguments. .pp the following table shows the equivalence between the arguments of .br clone () and the fields in the .i clone_args argument supplied to .br clone3 (): .rs 4 .ts lb lb lb l l l li li l. clone() clone3() notes \ficl_args\fp field flags & \(ti0xff flags t{ for most flags; details below t} parent_tid pidfd see clone_pidfd child_tid child_tid see clone_child_settid parent_tid parent_tid see clone_parent_settid flags & 0xff exit_signal stack stack \fp---\fp stack_size tls tls see clone_settls \fp---\fp set_tid see below for details \fp---\fp set_tid_size \fp---\fp cgroup see clone_into_cgroup .te .re .\" .ss the child termination signal when the child process terminates, a signal may be sent to the parent. the termination signal is specified in the low byte of .i flags .rb ( clone ()) or in .i cl_args.exit_signal .rb ( clone3 ()). if this signal is specified as anything other than .br sigchld , then the parent process must specify the .b __wall or .b __wclone options when waiting for the child with .br wait (2). if no signal (i.e., zero) is specified, then the parent process is not signaled when the child terminates. .\" .ss the set_tid array by default, the kernel chooses the next sequential pid for the new process in each of the pid namespaces where it is present. when creating a process with .br clone3 (), the .i set_tid array (available since linux 5.5) can be used to select specific pids for the process in some or all of the pid namespaces where it is present. if the pid of the newly created process should be set only for the current pid namespace or in the newly created pid namespace (if .i flags contains .br clone_newpid ) then the first element in the .i set_tid array has to be the desired pid and .i set_tid_size needs to be 1. .pp if the pid of the newly created process should have a certain value in multiple pid namespaces, then the .i set_tid array can have multiple entries. the first entry defines the pid in the most deeply nested pid namespace and each of the following entries contains the pid in the corresponding ancestor pid namespace. the number of pid namespaces in which a pid should be set is defined by .i set_tid_size which cannot be larger than the number of currently nested pid namespaces. .pp to create a process with the following pids in a pid namespace hierarchy: .rs 4 .ts lb lb lb l l l. pid ns level requested pid notes 0 31496 outermost pid namespace 1 42 2 7 innermost pid namespace .te .re .pp set the array to: .pp .in +4n .ex set_tid[0] = 7; set_tid[1] = 42; set_tid[2] = 31496; set_tid_size = 3; .ee .in .pp if only the pids in the two innermost pid namespaces need to be specified, set the array to: .pp .in +4n .ex set_tid[0] = 7; set_tid[1] = 42; set_tid_size = 2; .ee .in .pp the pid in the pid namespaces outside the two innermost pid namespaces is selected the same way as any other pid is selected. .pp the .i set_tid feature requires .br cap_sys_admin or (since linux 5.9) .\" commit 124ea650d3072b005457faed69909221c2905a1f .\" commit 1caef81da05a84a40dbf02110e967ce6d1135ff6 .br cap_checkpoint_restore in all owning user namespaces of the target pid namespaces. .pp callers may only choose a pid greater than 1 in a given pid namespace if an .br init process (i.e., a process with pid 1) already exists in that namespace. otherwise the pid entry for this pid namespace must be 1. .\" .ss the flags mask both .br clone () and .br clone3 () allow a flags bit mask that modifies their behavior and allows the caller to specify what is shared between the calling process and the child process. this bit mask\(emthe .i flags argument of .br clone () or the .i cl_args.flags field passed to .br clone3 ()\(emis referred to as the .i flags mask in the remainder of this page. .pp the .i flags mask is specified as a bitwise-or of zero or more of the constants listed below. except as noted below, these flags are available (and have the same effect) in both .br clone () and .br clone3 (). .tp .br clone_child_cleartid " (since linux 2.5.49)" clear (zero) the child thread id at the location pointed to by .i child_tid .rb ( clone ()) or .i cl_args.child_tid .rb ( clone3 ()) in child memory when the child exits, and do a wakeup on the futex at that address. the address involved may be changed by the .br set_tid_address (2) system call. this is used by threading libraries. .tp .br clone_child_settid " (since linux 2.5.49)" store the child thread id at the location pointed to by .i child_tid .rb ( clone ()) or .i cl_args.child_tid .rb ( clone3 ()) in the child's memory. the store operation completes before the clone call returns control to user space in the child process. (note that the store operation may not have completed before the clone call returns in the parent process, which is relevant if the .br clone_vm flag is also employed.) .tp .br clone_clear_sighand " (since linux 5.5)" .\" commit b612e5df4587c934bd056bf05f4a1deca4de4f75 by default, signal dispositions in the child thread are the same as in the parent. if this flag is specified, then all signals that are handled in the parent are reset to their default dispositions .rb ( sig_dfl ) in the child. .ip specifying this flag together with .b clone_sighand is nonsensical and disallowed. .tp .br clone_detached " (historical)" for a while (during the linux 2.5 development series) .\" added in 2.5.32; removed in 2.6.0-test4 there was a .b clone_detached flag, which caused the parent not to receive a signal when the child terminated. ultimately, the effect of this flag was subsumed under the .br clone_thread flag and by the time linux 2.6.0 was released, this flag had no effect. starting in linux 2.6.2, the need to give this flag together with .b clone_thread disappeared. .ip this flag is still defined, but it is usually ignored when calling .br clone (). however, see the description of .br clone_pidfd for some exceptions. .tp .br clone_files " (since linux 2.0)" if .b clone_files is set, the calling process and the child process share the same file descriptor table. any file descriptor created by the calling process or by the child process is also valid in the other process. similarly, if one of the processes closes a file descriptor, or changes its associated flags (using the .br fcntl (2) .b f_setfd operation), the other process is also affected. if a process sharing a file descriptor table calls .br execve (2), its file descriptor table is duplicated (unshared). .ip if .b clone_files is not set, the child process inherits a copy of all file descriptors opened in the calling process at the time of the clone call. subsequent operations that open or close file descriptors, or change file descriptor flags, performed by either the calling process or the child process do not affect the other process. note, however, that the duplicated file descriptors in the child refer to the same open file descriptions as the corresponding file descriptors in the calling process, and thus share file offsets and file status flags (see .br open (2)). .tp .br clone_fs " (since linux 2.0)" if .b clone_fs is set, the caller and the child process share the same filesystem information. this includes the root of the filesystem, the current working directory, and the umask. any call to .br chroot (2), .br chdir (2), or .br umask (2) performed by the calling process or the child process also affects the other process. .ip if .b clone_fs is not set, the child process works on a copy of the filesystem information of the calling process at the time of the clone call. calls to .br chroot (2), .br chdir (2), or .br umask (2) performed later by one of the processes do not affect the other process. .tp .br clone_into_cgroup " (since linux 5.7)" .\" commit ef2c41cf38a7559bbf91af42d5b6a4429db8fc68 by default, a child process is placed in the same version 2 cgroup as its parent. the .b clone_into_cgroup flag allows the child process to be created in a different version 2 cgroup. (note that .br clone_into_cgroup has effect only for version 2 cgroups.) .ip in order to place the child process in a different cgroup, the caller specifies .br clone_into_cgroup in .i cl_args.flags and passes a file descriptor that refers to a version 2 cgroup in the .i cl_args.cgroup field. (this file descriptor can be obtained by opening a cgroup v2 directory using either the .b o_rdonly or the .b o_path flag.) note that all of the usual restrictions (described in .br cgroups (7)) on placing a process into a version 2 cgroup apply. .ip among the possible use cases for .br clone_into_cgroup are the following: .rs .ip * 3 spawning a process into a cgroup different from the parent's cgroup makes it possible for a service manager to directly spawn new services into dedicated cgroups. this eliminates the accounting jitter that would be caused if the child process was first created in the same cgroup as the parent and then moved into the target cgroup. furthermore, spawning the child process directly into a target cgroup is significantly cheaper than moving the child process into the target cgroup after it has been created. .ip * the .br clone_into_cgroup flag also allows the creation of frozen child processes by spawning them into a frozen cgroup. (see .br cgroups (7) for a description of the freezer controller.) .ip * for threaded applications (or even thread implementations which make use of cgroups to limit individual threads), it is possible to establish a fixed cgroup layout before spawning each thread directly into its target cgroup. .re .tp .br clone_io " (since linux 2.6.25)" if .b clone_io is set, then the new process shares an i/o context with the calling process. if this flag is not set, then (as with .br fork (2)) the new process has its own i/o context. .ip .\" the following based on text from jens axboe the i/o context is the i/o scope of the disk scheduler (i.e., what the i/o scheduler uses to model scheduling of a process's i/o). if processes share the same i/o context, they are treated as one by the i/o scheduler. as a consequence, they get to share disk time. for some i/o schedulers, .\" the anticipatory and cfq scheduler if two processes share an i/o context, they will be allowed to interleave their disk access. if several threads are doing i/o on behalf of the same process .rb ( aio_read (3), for instance), they should employ .br clone_io to get better i/o performance. .\" with cfq and as. .ip if the kernel is not configured with the .b config_block option, this flag is a no-op. .tp .br clone_newcgroup " (since linux 4.6)" create the process in a new cgroup namespace. if this flag is not set, then (as with .br fork (2)) the process is created in the same cgroup namespaces as the calling process. .ip for further information on cgroup namespaces, see .br cgroup_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newcgroup . .\" .tp .br clone_newipc " (since linux 2.6.19)" if .b clone_newipc is set, then create the process in a new ipc namespace. if this flag is not set, then (as with .br fork (2)), the process is created in the same ipc namespace as the calling process. .ip for further information on ipc namespaces, see .br ipc_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newipc . this flag can't be specified in conjunction with .br clone_sysvsem . .tp .br clone_newnet " (since linux 2.6.24)" (the implementation of this flag was completed only by about kernel version 2.6.29.) .ip if .b clone_newnet is set, then create the process in a new network namespace. if this flag is not set, then (as with .br fork (2)) the process is created in the same network namespace as the calling process. .ip for further information on network namespaces, see .br network_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newnet . .tp .br clone_newns " (since linux 2.4.19)" if .b clone_newns is set, the cloned child is started in a new mount namespace, initialized with a copy of the namespace of the parent. if .b clone_newns is not set, the child lives in the same mount namespace as the parent. .ip for further information on mount namespaces, see .br namespaces (7) and .br mount_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newns . it is not permitted to specify both .b clone_newns and .b clone_fs .\" see https://lwn.net/articles/543273/ in the same clone call. .tp .br clone_newpid " (since linux 2.6.24)" .\" this explanation draws a lot of details from .\" http://lwn.net/articles/259217/ .\" authors: pavel emelyanov .\" and kir kolyshkin .\" .\" the primary kernel commit is 30e49c263e36341b60b735cbef5ca37912549264 .\" author: pavel emelyanov if .b clone_newpid is set, then create the process in a new pid namespace. if this flag is not set, then (as with .br fork (2)) the process is created in the same pid namespace as the calling process. .ip for further information on pid namespaces, see .br namespaces (7) and .br pid_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newpid . this flag can't be specified in conjunction with .br clone_thread or .br clone_parent . .tp .br clone_newuser (this flag first became meaningful for .br clone () in linux 2.6.23, the current .br clone () semantics were merged in linux 3.5, and the final pieces to make the user namespaces completely usable were merged in linux 3.8.) .ip if .b clone_newuser is set, then create the process in a new user namespace. if this flag is not set, then (as with .br fork (2)) the process is created in the same user namespace as the calling process. .ip for further information on user namespaces, see .br namespaces (7) and .br user_namespaces (7). .ip before linux 3.8, use of .br clone_newuser required that the caller have three capabilities: .br cap_sys_admin , .br cap_setuid , and .br cap_setgid . .\" before linux 2.6.29, it appears that only cap_sys_admin was needed starting with linux 3.8, no privileges are needed to create a user namespace. .ip this flag can't be specified in conjunction with .br clone_thread or .br clone_parent . for security reasons, .\" commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71 .\" https://lwn.net/articles/543273/ .\" the fix actually went into 3.9 and into 3.8.3. however, user namespaces .\" were, for practical purposes, unusable in earlier 3.8.x because of the .\" various filesystems that didn't support userns. .br clone_newuser cannot be specified in conjunction with .br clone_fs . .tp .br clone_newuts " (since linux 2.6.19)" if .b clone_newuts is set, then create the process in a new uts namespace, whose identifiers are initialized by duplicating the identifiers from the uts namespace of the calling process. if this flag is not set, then (as with .br fork (2)) the process is created in the same uts namespace as the calling process. .ip for further information on uts namespaces, see .br uts_namespaces (7). .ip only a privileged process .rb ( cap_sys_admin ) can employ .br clone_newuts . .tp .br clone_parent " (since linux 2.3.12)" if .b clone_parent is set, then the parent of the new child (as returned by .br getppid (2)) will be the same as that of the calling process. .ip if .b clone_parent is not set, then (as with .br fork (2)) the child's parent is the calling process. .ip note that it is the parent process, as returned by .br getppid (2), which is signaled when the child terminates, so that if .b clone_parent is set, then the parent of the calling process, rather than the calling process itself, is signaled. .ip the .b clone_parent flag can't be used in clone calls by the global init process (pid 1 in the initial pid namespace) and init processes in other pid namespaces. this restriction prevents the creation of multi-rooted process trees as well as the creation of unreapable zombies in the initial pid namespace. .tp .br clone_parent_settid " (since linux 2.5.49)" store the child thread id at the location pointed to by .i parent_tid .rb ( clone ()) or .i cl_args.parent_tid .rb ( clone3 ()) in the parent's memory. (in linux 2.5.32-2.5.48 there was a flag .b clone_settid that did this.) the store operation completes before the clone call returns control to user space. .tp .br clone_pid " (linux 2.0 to 2.5.15)" if .b clone_pid is set, the child process is created with the same process id as the calling process. this is good for hacking the system, but otherwise of not much use. from linux 2.3.21 onward, this flag could be specified only by the system boot process (pid 0). the flag disappeared completely from the kernel sources in linux 2.5.16. subsequently, the kernel silently ignored this bit if it was specified in the .ir flags mask. much later, the same bit was recycled for use as the .b clone_pidfd flag. .tp .br clone_pidfd " (since linux 5.2)" .\" commit b3e5838252665ee4cfa76b82bdf1198dca81e5be if this flag is specified, a pid file descriptor referring to the child process is allocated and placed at a specified location in the parent's memory. the close-on-exec flag is set on this new file descriptor. pid file descriptors can be used for the purposes described in .br pidfd_open (2). .rs .ip * 3 when using .br clone3 (), the pid file descriptor is placed at the location pointed to by .ir cl_args.pidfd . .ip * when using .br clone (), the pid file descriptor is placed at the location pointed to by .ir parent_tid . since the .i parent_tid argument is used to return the pid file descriptor, .b clone_pidfd cannot be used with .b clone_parent_settid when calling .br clone (). .re .ip it is currently not possible to use this flag together with .b clone_thread. this means that the process identified by the pid file descriptor will always be a thread group leader. .ip if the obsolete .b clone_detached flag is specified alongside .br clone_pidfd when calling .br clone (), an error is returned. an error also results if .b clone_detached is specified when calling .br clone3 (). this error behavior ensures that the bit corresponding to .br clone_detached can be reused for further pid file descriptor features in the future. .tp .br clone_ptrace " (since linux 2.2)" if .b clone_ptrace is specified, and the calling process is being traced, then trace the child also (see .br ptrace (2)). .tp .br clone_settls " (since linux 2.5.32)" the tls (thread local storage) descriptor is set to .ir tls . .ip the interpretation of .i tls and the resulting effect is architecture dependent. on x86, .i tls is interpreted as a .ir "struct user_desc\ *" (see .br set_thread_area (2)). on x86-64 it is the new value to be set for the %fs base register (see the .b arch_set_fs argument to .br arch_prctl (2)). on architectures with a dedicated tls register, it is the new value of that register. .ip use of this flag requires detailed knowledge and generally it should not be used except in libraries implementing threading. .tp .br clone_sighand " (since linux 2.0)" if .b clone_sighand is set, the calling process and the child process share the same table of signal handlers. if the calling process or child process calls .br sigaction (2) to change the behavior associated with a signal, the behavior is changed in the other process as well. however, the calling process and child processes still have distinct signal masks and sets of pending signals. so, one of them may block or unblock signals using .br sigprocmask (2) without affecting the other process. .ip if .b clone_sighand is not set, the child process inherits a copy of the signal handlers of the calling process at the time of the clone call. calls to .br sigaction (2) performed later by one of the processes have no effect on the other process. .ip since linux 2.6.0, .\" precisely: linux 2.6.0-test6 the .i flags mask must also include .b clone_vm if .b clone_sighand is specified. .tp .br clone_stopped " (since linux 2.6.0)" .\" precisely: linux 2.6.0-test2 if .b clone_stopped is set, then the child is initially stopped (as though it was sent a .b sigstop signal), and must be resumed by sending it a .b sigcont signal. .ip this flag was .i deprecated from linux 2.6.25 onward, and was .i removed altogether in linux 2.6.38. since then, the kernel silently ignores it without error. .\" glibc 2.8 removed this defn from bits/sched.h starting with linux 4.6, the same bit was reused for the .br clone_newcgroup flag. .tp .br clone_sysvsem " (since linux 2.5.10)" if .b clone_sysvsem is set, then the child and the calling process share a single list of system v semaphore adjustment .ri ( semadj ) values (see .br semop (2)). in this case, the shared list accumulates .i semadj values across all processes sharing the list, and semaphore adjustments are performed only when the last process that is sharing the list terminates (or ceases sharing the list using .br unshare (2)). if this flag is not set, then the child has a separate .i semadj list that is initially empty. .tp .br clone_thread " (since linux 2.4.0)" .\" precisely: linux 2.6.0-test8 if .b clone_thread is set, the child is placed in the same thread group as the calling process. to make the remainder of the discussion of .b clone_thread more readable, the term "thread" is used to refer to the processes within a thread group. .ip thread groups were a feature added in linux 2.4 to support the posix threads notion of a set of threads that share a single pid. internally, this shared pid is the so-called thread group identifier (tgid) for the thread group. since linux 2.4, calls to .br getpid (2) return the tgid of the caller. .ip the threads within a group can be distinguished by their (system-wide) unique thread ids (tid). a new thread's tid is available as the function result returned to the caller, and a thread can obtain its own tid using .br gettid (2). .ip when a clone call is made without specifying .br clone_thread , then the resulting thread is placed in a new thread group whose tgid is the same as the thread's tid. this thread is the .i leader of the new thread group. .ip a new thread created with .b clone_thread has the same parent process as the process that made the clone call (i.e., like .br clone_parent ), so that calls to .br getppid (2) return the same value for all of the threads in a thread group. when a .b clone_thread thread terminates, the thread that created it is not sent a .b sigchld (or other termination) signal; nor can the status of such a thread be obtained using .br wait (2). (the thread is said to be .ir detached .) .ip after all of the threads in a thread group terminate the parent process of the thread group is sent a .b sigchld (or other termination) signal. .ip if any of the threads in a thread group performs an .br execve (2), then all threads other than the thread group leader are terminated, and the new program is executed in the thread group leader. .ip if one of the threads in a thread group creates a child using .br fork (2), then any thread in the group can .br wait (2) for that child. .ip since linux 2.5.35, the .i flags mask must also include .b clone_sighand if .b clone_thread is specified (and note that, since linux 2.6.0, .\" precisely: linux 2.6.0-test6 .br clone_sighand also requires .br clone_vm to be included). .ip signal dispositions and actions are process-wide: if an unhandled signal is delivered to a thread, then it will affect (terminate, stop, continue, be ignored in) all members of the thread group. .ip each thread has its own signal mask, as set by .br sigprocmask (2). .ip a signal may be process-directed or thread-directed. a process-directed signal is targeted at a thread group (i.e., a tgid), and is delivered to an arbitrarily selected thread from among those that are not blocking the signal. a signal may be process-directed because it was generated by the kernel for reasons other than a hardware exception, or because it was sent using .br kill (2) or .br sigqueue (3). a thread-directed signal is targeted at (i.e., delivered to) a specific thread. a signal may be thread directed because it was sent using .br tgkill (2) or .br pthread_sigqueue (3), or because the thread executed a machine language instruction that triggered a hardware exception (e.g., invalid memory access triggering .br sigsegv or a floating-point exception triggering .br sigfpe ). .ip a call to .br sigpending (2) returns a signal set that is the union of the pending process-directed signals and the signals that are pending for the calling thread. .ip if a process-directed signal is delivered to a thread group, and the thread group has installed a handler for the signal, then the handler is invoked in exactly one, arbitrarily selected member of the thread group that has not blocked the signal. if multiple threads in a group are waiting to accept the same signal using .br sigwaitinfo (2), the kernel will arbitrarily select one of these threads to receive the signal. .tp .br clone_untraced " (since linux 2.5.46)" if .b clone_untraced is specified, then a tracing process cannot force .b clone_ptrace on this child process. .tp .br clone_vfork " (since linux 2.2)" if .b clone_vfork is set, the execution of the calling process is suspended until the child releases its virtual memory resources via a call to .br execve (2) or .br _exit (2) (as with .br vfork (2)). .ip if .b clone_vfork is not set, then both the calling process and the child are schedulable after the call, and an application should not rely on execution occurring in any particular order. .tp .br clone_vm " (since linux 2.0)" if .b clone_vm is set, the calling process and the child process run in the same memory space. in particular, memory writes performed by the calling process or by the child process are also visible in the other process. moreover, any memory mapping or unmapping performed with .br mmap (2) or .br munmap (2) by the child or calling process also affects the other process. .ip if .b clone_vm is not set, the child process runs in a separate copy of the memory space of the calling process at the time of the clone call. memory writes or file mappings/unmappings performed by one of the processes do not affect the other, as with .br fork (2). .ip if the .br clone_vm flag is specified and the .br clone_vfork flag is not specified, then any alternate signal stack that was established by .br sigaltstack (2) is cleared in the child process. .sh return value .\" gettid(2) returns current->pid; .\" getpid(2) returns current->tgid; on success, the thread id of the child process is returned in the caller's thread of execution. on failure, \-1 is returned in the caller's context, no child process is created, and .i errno is set to indicate the error. .sh errors .tp .b eagain too many processes are already running; see .br fork (2). .tp .br ebusy " (" clone3 "() only)" .b clone_into_cgroup was specified in .ir cl_args.flags , but the file descriptor specified in .ir cl_args.cgroup refers to a version 2 cgroup in which a domain controller is enabled. .tp .br eexist " (" clone3 "() only)" one (or more) of the pids specified in .i set_tid already exists in the corresponding pid namespace. .tp .b einval both .b clone_sighand and .b clone_clear_sighand were specified in the .i flags mask. .tp .b einval .b clone_sighand was specified in the .i flags mask, but .b clone_vm was not. (since linux 2.6.0.) .\" precisely: linux 2.6.0-test6 .tp .b einval .b clone_thread was specified in the .i flags mask, but .b clone_sighand was not. (since linux 2.5.35.) .\" .tp .\" .b einval .\" precisely one of .\" .b clone_detached .\" and .\" .b clone_thread .\" was specified. .\" (since linux 2.6.0-test6.) .tp .b einval .b clone_thread was specified in the .i flags mask, but the current process previously called .br unshare (2) with the .b clone_newpid flag or used .br setns (2) to reassociate itself with a pid namespace. .tp .b einval .\" commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71 both .b clone_fs and .b clone_newns were specified in the .ir flags mask. .tp .br einval " (since linux 3.9)" both .b clone_newuser and .b clone_fs were specified in the .ir flags mask. .tp .b einval both .b clone_newipc and .b clone_sysvsem were specified in the .ir flags mask. .tp .b einval one (or both) of .br clone_newpid or .br clone_newuser and one (or both) of .br clone_thread or .br clone_parent were specified in the .ir flags mask. .tp .br einval " (since linux 2.6.32)" .\" commit 123be07b0b399670a7cc3d82fef0cb4f93ef885c .br clone_parent was specified, and the caller is an init process. .tp .b einval returned by the glibc .br clone () wrapper function when .ir fn or .ir stack is specified as null. .tp .b einval .br clone_newipc was specified in the .ir flags mask, but the kernel was not configured with the .b config_sysvipc and .br config_ipc_ns options. .tp .b einval .br clone_newnet was specified in the .ir flags mask, but the kernel was not configured with the .b config_net_ns option. .tp .b einval .br clone_newpid was specified in the .ir flags mask, but the kernel was not configured with the .b config_pid_ns option. .tp .b einval .br clone_newuser was specified in the .ir flags mask, but the kernel was not configured with the .b config_user_ns option. .tp .b einval .br clone_newuts was specified in the .ir flags mask, but the kernel was not configured with the .b config_uts_ns option. .tp .b einval .i stack is not aligned to a suitable boundary for this architecture. for example, on aarch64, .i stack must be a multiple of 16. .tp .br einval " (" clone3 "() only)" .b clone_detached was specified in the .i flags mask. .tp .br einval " (" clone "() only)" .b clone_pidfd was specified together with .b clone_detached in the .i flags mask. .tp .b einval .b clone_pidfd was specified together with .b clone_thread in the .i flags mask. .tp .br "einval " "(" clone "() only)" .b clone_pidfd was specified together with .b clone_parent_settid in the .i flags mask. .tp .br einval " (" clone3 "() only)" .i set_tid_size is greater than the number of nested pid namespaces. .tp .br einval " (" clone3 "() only)" one of the pids specified in .i set_tid was an invalid. .tp .br einval " (aarch64 only, linux 4.6 and earlier)" .i stack was not aligned to a 128-bit boundary. .tp .b enomem cannot allocate sufficient memory to allocate a task structure for the child, or to copy those parts of the caller's context that need to be copied. .tp .br enospc " (since linux 3.7)" .\" commit f2302505775fd13ba93f034206f1e2a587017929 .b clone_newpid was specified in the .i flags mask, but the limit on the nesting depth of pid namespaces would have been exceeded; see .br pid_namespaces (7). .tp .br enospc " (since linux 4.9; beforehand " eusers ) .b clone_newuser was specified in the .ir flags mask, and the call would cause the limit on the number of nested user namespaces to be exceeded. see .br user_namespaces (7). .ip from linux 3.11 to linux 4.8, the error diagnosed in this case was .br eusers . .tp .br enospc " (since linux 4.9)" one of the values in the .i flags mask specified the creation of a new user namespace, but doing so would have caused the limit defined by the corresponding file in .ir /proc/sys/user to be exceeded. for further details, see .br namespaces (7). .tp .br eopnotsupp " (" clone3 "() only)" .b clone_into_cgroup was specified in .ir cl_args.flags , but the file descriptor specified in .ir cl_args.cgroup refers to a version 2 cgroup that is in the .ir "domain invalid" state. .tp .b eperm .br clone_newcgroup , .br clone_newipc , .br clone_newnet , .br clone_newns , .br clone_newpid , or .br clone_newuts was specified by an unprivileged process (process without \fbcap_sys_admin\fp). .tp .b eperm .b clone_pid was specified by a process other than process 0. (this error occurs only on linux 2.5.15 and earlier.) .tp .b eperm .br clone_newuser was specified in the .ir flags mask, but either the effective user id or the effective group id of the caller does not have a mapping in the parent namespace (see .br user_namespaces (7)). .tp .br eperm " (since linux 3.9)" .\" commit 3151527ee007b73a0ebd296010f1c0454a919c7d .b clone_newuser was specified in the .i flags mask and the caller is in a chroot environment .\" fixme what is the rationale for this restriction? (i.e., the caller's root directory does not match the root directory of the mount namespace in which it resides). .tp .br eperm " (" clone3 "() only)" .i set_tid_size was greater than zero, and the caller lacks the .b cap_sys_admin capability in one or more of the user namespaces that own the corresponding pid namespaces. .tp .br erestartnointr " (since linux 2.6.17)" .\" commit 4a2c7a7837da1b91468e50426066d988050e4d56 system call was interrupted by a signal and will be restarted. (this can be seen only during a trace.) .tp .br eusers " (linux 3.11 to linux 4.8)" .b clone_newuser was specified in the .ir flags mask, and the limit on the number of nested user namespaces would be exceeded. see the discussion of the .br enospc error above. .sh versions the .br clone3 () system call first appeared in linux 5.3. .\" there is no entry for .\" .br clone () .\" in libc5. .\" glibc2 provides .\" .br clone () .\" as described in this manual page. .sh conforming to these system calls are linux-specific and should not be used in programs intended to be portable. .sh notes one use of these systems calls is to implement threads: multiple flows of control in a program that run concurrently in a shared address space. .pp note that the glibc .br clone () wrapper function makes some changes in the memory pointed to by .i stack (changes required to set the stack up correctly for the child) .i before invoking the .br clone () system call. so, in cases where .br clone () is used to recursively create children, do not use the buffer employed for the parent's stack as the stack of the child. .pp the .br kcmp (2) system call can be used to test whether two processes share various resources such as a file descriptor table, system v semaphore undo operations, or a virtual address space. .pp handlers registered using .br pthread_atfork (3) are not executed during a clone call. .pp in the linux 2.4.x series, .b clone_thread generally does not make the parent of the new thread the same as the parent of the calling process. however, for kernel versions 2.4.7 to 2.4.18 the .b clone_thread flag implied the .b clone_parent flag (as in linux 2.6.0 and later). .pp on i386, .br clone () should not be called through vsyscall, but directly through .ir "int $0x80" . .\" .ss c library/kernel differences the raw .br clone () system call corresponds more closely to .br fork (2) in that execution in the child continues from the point of the call. as such, the .i fn and .i arg arguments of the .br clone () wrapper function are omitted. .pp in contrast to the glibc wrapper, the raw .br clone () system call accepts null as a .i stack argument (and .br clone3 () likewise allows .i cl_args.stack to be null). in this case, the child uses a duplicate of the parent's stack. (copy-on-write semantics ensure that the child gets separate copies of stack pages when either process modifies the stack.) in this case, for correct operation, the .b clone_vm option should not be specified. (if the child .i shares the parent's memory because of the use of the .br clone_vm flag, then no copy-on-write duplication occurs and chaos is likely to result.) .pp the order of the arguments also differs in the raw system call, and there are variations in the arguments across architectures, as detailed in the following paragraphs. .pp the raw system call interface on x86-64 and some other architectures (including sh, tile, and alpha) is: .pp .in +4n .ex .bi "long clone(unsigned long " flags ", void *" stack , .bi " int *" parent_tid ", int *" child_tid , .bi " unsigned long " tls ); .ee .in .pp on x86-32, and several other common architectures (including score, arm, arm 64, pa-risc, arc, power pc, xtensa, and mips), .\" config_clone_backwards the order of the last two arguments is reversed: .pp .in +4n .ex .bi "long clone(unsigned long " flags ", void *" stack , .bi " int *" parent_tid ", unsigned long " tls , .bi " int *" child_tid ); .ee .in .pp on the cris and s390 architectures, .\" config_clone_backwards2 the order of the first two arguments is reversed: .pp .in +4n .ex .bi "long clone(void *" stack ", unsigned long " flags , .bi " int *" parent_tid ", int *" child_tid , .bi " unsigned long " tls ); .ee .in .pp on the microblaze architecture, .\" config_clone_backwards3 an additional argument is supplied: .pp .in +4n .ex .bi "long clone(unsigned long " flags ", void *" stack , .bi " int " stack_size , "\fr /* size of stack */" .bi " int *" parent_tid ", int *" child_tid , .bi " unsigned long " tls ); .ee .in .\" .ss blackfin, m68k, and sparc .\" mike frysinger noted in a 2013 mail: .\" these arches don't define __arch_want_sys_clone: .\" blackfin ia64 m68k sparc the argument-passing conventions on blackfin, m68k, and sparc are different from the descriptions above. for details, see the kernel (and glibc) source. .ss ia64 on ia64, a different interface is used: .pp .in +4n .ex .bi "int __clone2(int (*" "fn" ")(void *)," .bi " void *" stack_base ", size_t " stack_size , .bi " int " flags ", void *" "arg" ", ..." .bi " /* pid_t *" parent_tid ", struct user_desc *" tls , .bi " pid_t *" child_tid " */ );" .ee .in .pp the prototype shown above is for the glibc wrapper function; for the system call itself, the prototype can be described as follows (it is identical to the .br clone () prototype on microblaze): .pp .in +4n .ex .bi "long clone2(unsigned long " flags ", void *" stack_base , .bi " int " stack_size , "\fr /* size of stack */" .bi " int *" parent_tid ", int *" child_tid , .bi " unsigned long " tls ); .ee .in .pp .br __clone2 () operates in the same way as .br clone (), except that .i stack_base points to the lowest address of the child's stack area, and .i stack_size specifies the size of the stack pointed to by .ir stack_base . .ss linux 2.4 and earlier in linux 2.4 and earlier, .br clone () does not take arguments .ir parent_tid , .ir tls , and .ir child_tid . .sh bugs gnu c library versions 2.3.4 up to and including 2.24 contained a wrapper function for .br getpid (2) that performed caching of pids. this caching relied on support in the glibc wrapper for .br clone (), but limitations in the implementation meant that the cache was not up to date in some circumstances. in particular, if a signal was delivered to the child immediately after the .br clone () call, then a call to .br getpid (2) in a handler for the signal could return the pid of the calling process ("the parent"), if the clone wrapper had not yet had a chance to update the pid cache in the child. (this discussion ignores the case where the child was created using .br clone_thread , when .br getpid (2) .i should return the same value in the child and in the process that called .br clone (), since the caller and the child are in the same thread group. the stale-cache problem also does not occur if the .i flags argument includes .br clone_vm .) to get the truth, it was sometimes necessary to use code such as the following: .pp .in +4n .ex #include pid_t mypid; mypid = syscall(sys_getpid); .ee .in .\" see also the following bug reports .\" https://bugzilla.redhat.com/show_bug.cgi?id=417521 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=6910 .pp because of the stale-cache problem, as well as other problems noted in .br getpid (2), the pid caching feature was removed in glibc 2.25. .sh examples the following program demonstrates the use of .br clone () to create a child process that executes in a separate uts namespace. the child changes the hostname in its uts namespace. both parent and child then display the system hostname, making it possible to see that the hostname differs in the uts namespaces of the parent and child. for an example of the use of this program, see .br setns (2). .pp within the sample program, we allocate the memory that is to be used for the child's stack using .br mmap (2) rather than .br malloc (3) for the following reasons: .ip * 3 .br mmap (2) allocates a block of memory that starts on a page boundary and is a multiple of the page size. this is useful if we want to establish a guard page (a page with protection .br prot_none ) at the end of the stack using .br mprotect (2). .ip * we can specify the .br map_stack flag to request a mapping that is suitable for a stack. for the moment, this flag is a no-op on linux, but it exists and has effect on some other systems, so we should include it for portability. .ss program source .ex #define _gnu_source #include #include #include #include #include #include #include #include #include #define errexit(msg) do { perror(msg); exit(exit_failure); \e } while (0) static int /* start function for cloned child */ childfunc(void *arg) { struct utsname uts; /* change hostname in uts namespace of child. */ if (sethostname(arg, strlen(arg)) == \-1) errexit("sethostname"); /* retrieve and display hostname. */ if (uname(&uts) == \-1) errexit("uname"); printf("uts.nodename in child: %s\en", uts.nodename); /* keep the namespace open for a while, by sleeping. this allows some experimentation\-\-for example, another process might join the namespace. */ sleep(200); return 0; /* child terminates now */ } #define stack_size (1024 * 1024) /* stack size for cloned child */ int main(int argc, char *argv[]) { char *stack; /* start of stack buffer */ char *stacktop; /* end of stack buffer */ pid_t pid; struct utsname uts; if (argc < 2) { fprintf(stderr, "usage: %s \en", argv[0]); exit(exit_success); } /* allocate memory to be used for the stack of the child. */ stack = mmap(null, stack_size, prot_read | prot_write, map_private | map_anonymous | map_stack, \-1, 0); if (stack == map_failed) errexit("mmap"); stacktop = stack + stack_size; /* assume stack grows downward */ /* create child that has its own uts namespace; child commences execution in childfunc(). */ pid = clone(childfunc, stacktop, clone_newuts | sigchld, argv[1]); if (pid == \-1) errexit("clone"); printf("clone() returned %jd\en", (intmax_t) pid); /* parent falls through to here */ sleep(1); /* give child time to change its hostname */ /* display hostname in parent\(aqs uts namespace. this will be different from hostname in child\(aqs uts namespace. */ if (uname(&uts) == \-1) errexit("uname"); printf("uts.nodename in parent: %s\en", uts.nodename); if (waitpid(pid, null, 0) == \-1) /* wait for child */ errexit("waitpid"); printf("child has terminated\en"); exit(exit_success); } .ee .sh see also .br fork (2), .br futex (2), .br getpid (2), .br gettid (2), .br kcmp (2), .br mmap (2), .br pidfd_open (2), .br set_thread_area (2), .br set_tid_address (2), .br setns (2), .br tkill (2), .br unshare (2), .br wait (2), .br capabilities (7), .br namespaces (7), .br pthreads (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/rpc.3 .\" copyright 2003,2004 andi kleen, suse labs. .\" and copyright 2007 lee schermerhorn, hewlett packard .\" .\" %%%license_start(verbatim_prof) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" 2006-02-03, mtk, substantial wording changes and other improvements .\" 2007-08-27, lee schermerhorn .\" more precise specification of behavior. .\" .th get_mempolicy 2 2021-03-22 linux "linux programmer's manual" .sh name get_mempolicy \- retrieve numa memory policy for a thread .sh synopsis .b "#include " .nf .pp .bi "long get_mempolicy(int *" mode ", unsigned long *" nodemask , .bi " unsigned long " maxnode ", void *" addr , .bi " unsigned long " flags ); .pp link with \fi\-lnuma\fp. .fi .pp .ir note : there is no glibc wrapper for this system call; see notes. .sh description .br get_mempolicy () retrieves the numa policy of the calling thread or of a memory address, depending on the setting of .ir flags . .pp a numa machine has different memory controllers with different distances to specific cpus. the memory policy defines from which node memory is allocated for the thread. .pp if .i flags is specified as 0, then information about the calling thread's default policy (as set by .br set_mempolicy (2)) is returned, in the buffers pointed to by .i mode and .ir nodemask . the value returned in these arguments may be used to restore the thread's policy to its state at the time of the call to .br get_mempolicy () using .br set_mempolicy (2). when .i flags is 0, .i addr must be specified as null. .pp if .i flags specifies .br mpol_f_mems_allowed (available since linux 2.6.24), the .i mode argument is ignored and the set of nodes (memories) that the thread is allowed to specify in subsequent calls to .br mbind (2) or .br set_mempolicy (2) (in the absence of any .ir "mode flags" ) is returned in .ir nodemask . it is not permitted to combine .b mpol_f_mems_allowed with either .b mpol_f_addr or .br mpol_f_node . .pp if .i flags specifies .br mpol_f_addr , then information is returned about the policy governing the memory address given in .ir addr . this policy may be different from the thread's default policy if .br mbind (2) or one of the helper functions described in .br numa (3) has been used to establish a policy for the memory range containing .ir addr . .pp if the .i mode argument is not null, then .br get_mempolicy () will store the policy mode and any optional .i "mode flags" of the requested numa policy in the location pointed to by this argument. if .i nodemask is not null, then the nodemask associated with the policy will be stored in the location pointed to by this argument. .i maxnode specifies the number of node ids that can be stored into .ir nodemask \(emthat is, the maximum node id plus one. the value specified by .i maxnode is always rounded to a multiple of .ir "sizeof(unsigned\ long)*8" . .pp if .i flags specifies both .b mpol_f_node and .br mpol_f_addr , .br get_mempolicy () will return the node id of the node on which the address .i addr is allocated into the location pointed to by .ir mode . if no page has yet been allocated for the specified address, .br get_mempolicy () will allocate a page as if the thread had performed a read (load) access to that address, and return the id of the node where that page was allocated. .pp if .i flags specifies .br mpol_f_node , but not .br mpol_f_addr , and the thread's current policy is .br mpol_interleave , then .br get_mempolicy () will return in the location pointed to by a non-null .i mode argument, the node id of the next node that will be used for interleaving of internal kernel pages allocated on behalf of the thread. .\" note: code returns next interleave node via 'mode' argument -lee schermerhorn these allocations include pages for memory-mapped files in process memory ranges mapped using the .br mmap (2) call with the .b map_private flag for read accesses, and in memory ranges mapped with the .b map_shared flag for all accesses. .pp other flag values are reserved. .pp for an overview of the possible policies see .br set_mempolicy (2). .sh return value on success, .br get_mempolicy () returns 0; on error, \-1 is returned and .i errno is set to indicate the error. .sh errors .tp .b efault part of all of the memory range specified by .i nodemask and .i maxnode points outside your accessible address space. .tp .b einval the value specified by .i maxnode is less than the number of node ids supported by the system. or .i flags specified values other than .b mpol_f_node or .br mpol_f_addr ; or .i flags specified .b mpol_f_addr and .i addr is null, or .i flags did not specify .b mpol_f_addr and .i addr is not null. or, .i flags specified .b mpol_f_node but not .b mpol_f_addr and the current thread policy is not .br mpol_interleave . or, .i flags specified .b mpol_f_mems_allowed with either .b mpol_f_addr or .br mpol_f_node . (and there are other .b einval cases.) .sh versions the .br get_mempolicy () system call was added to the linux kernel in version 2.6.7. .sh conforming to this system call is linux-specific. .sh notes glibc does not provide a wrapper for this system call. for information on library support, see .br numa (7). .sh see also .br getcpu (2), .br mbind (2), .br mmap (2), .br set_mempolicy (2), .br numa (3), .br numa (7), .br numactl (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th mblen 3 2021-03-22 "gnu" "linux programmer's manual" .sh name mblen \- determine number of bytes in next multibyte character .sh synopsis .nf .b #include .pp .bi "int mblen(const char *" s ", size_t " n ); .fi .sh description if .i s is not null, the .br mblen () function inspects at most .i n bytes of the multibyte string starting at .i s and extracts the next complete multibyte character. it uses a static anonymous shift state known only to the .br mblen () function. if the multibyte character is not the null wide character, it returns the number of bytes that were consumed from .ir s . if the multibyte character is the null wide character, it returns 0. .pp if the .ir n bytes starting at .i s do not contain a complete multibyte character, .br mblen () returns \-1. this can happen even if .i n is greater than or equal to .ir mb_cur_max , if the multibyte string contains redundant shift sequences. .pp if the multibyte string starting at .i s contains an invalid multibyte sequence before the next complete character, .br mblen () also returns \-1. .pp if .i s is null, the .br mblen () function .\" the dinkumware doc and the single unix specification say this, but .\" glibc doesn't implement this. resets the shift state, known to only this function, to the initial state, and returns nonzero if the encoding has nontrivial shift state, or zero if the encoding is stateless. .sh return value the .br mblen () function returns the number of bytes parsed from the multibyte sequence starting at .ir s , if a non-null wide character was recognized. it returns 0, if a null wide character was recognized. it returns \-1, if an invalid multibyte sequence was encountered or if it couldn't parse a complete multibyte character. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br mblen () t} thread safety mt-unsafe race .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh notes the behavior of .br mblen () depends on the .b lc_ctype category of the current locale. .pp the function .br mbrlen (3) provides a better interface to the same functionality. .sh see also .br mbrlen (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/strfromd.3 .so man2/eventfd.2 .so man3/printf.3 .\" copyright (c) 2004 andries brouwer (aeb@cwi.nl) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th exit_group 2 2021-06-20 "linux" "linux programmer's manual" .sh name exit_group \- exit all threads in a process .sh synopsis .nf .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "noreturn void syscall(sys_exit_group, int " status ); .fi .pp .ir note : glibc provides no wrapper for .br exit_group (), necessitating the use of .br syscall (2). .sh description this system call is equivalent to .br _exit (2) except that it terminates not only the calling thread, but all threads in the calling process's thread group. .sh return value this system call does not return. .sh versions this call is present since linux 2.5.35. .sh conforming to this call is linux-specific. .sh notes since glibc 2.3, this is the system call invoked when the .br _exit (2) wrapper function is called. .sh see also .br exit (2) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/exec.3 .\" copyright (c) 1993 by thomas koenig (ig25@rz.uni-karlsruhe.de) .\" and copyright (c) 2008 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified sat jul 24 18:40:56 1993 by rik faith (faith@cs.unc.edu) .\" modified 1995 by mike battersby (mib@deakin.edu.au) .\" .th raise 3 2021-03-22 "gnu" "linux programmer's manual" .sh name raise \- send a signal to the caller .sh synopsis .nf .b #include .pp .bi "int raise(int " sig ); .fi .sh description the .br raise () function sends a signal to the calling process or thread. in a single-threaded program it is equivalent to .pp .in +4n .ex kill(getpid(), sig); .ee .in .pp in a multithreaded program it is equivalent to .pp .in +4n .ex pthread_kill(pthread_self(), sig); .ee .in .pp if the signal causes a handler to be called, .br raise () will return only after the signal handler has returned. .sh return value .br raise () returns 0 on success, and nonzero for failure. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br raise () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c89, c99. .sh notes since version 2.3.3, glibc implements .br raise () by calling .br tgkill (2), .\" 2.3.2 used the obsolete tkill(), if available. if the kernel supports that system call. older glibc versions implemented .br raise () using .br kill (2). .sh see also .br getpid (2), .br kill (2), .br sigaction (2), .br signal (2), .br pthread_kill (3), .br signal (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1993 by thomas koenig (ig25@rz.uni-karlsruhe.de) .\" and copyright (c) 2002, 2006, 2020 by michael kerrisk .\" and copyright (c) 2008 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified sat jul 24 17:34:08 1993 by rik faith (faith@cs.unc.edu) .\" modified sun jan 7 01:41:27 1996 by andries brouwer (aeb@cwi.nl) .\" modified sun apr 14 12:02:29 1996 by andries brouwer (aeb@cwi.nl) .\" modified sat nov 13 16:28:23 1999 by andries brouwer (aeb@cwi.nl) .\" modified 10 apr 2002, by michael kerrisk .\" modified 7 jun 2002, by michael kerrisk .\" added information on real-time signals .\" modified 13 jun 2002, by michael kerrisk .\" noted that sigstkflt is in fact unused .\" 2004-12-03, modified mtk, added notes on rlimit_sigpending .\" 2006-04-24, mtk, added text on changing signal dispositions, .\" signal mask, and pending signals. .\" 2008-07-04, mtk: .\" added section on system call restarting (sa_restart) .\" added section on stop/cont signals interrupting syscalls. .\" 2008-10-05, mtk: various additions .\" .th signal 7 2021-03-22 "linux" "linux programmer's manual" .sh name signal \- overview of signals .sh description linux supports both posix reliable signals (hereinafter "standard signals") and posix real-time signals. .ss signal dispositions each signal has a current .ir disposition , which determines how the process behaves when it is delivered the signal. .pp the entries in the "action" column of the table below specify the default disposition for each signal, as follows: .ip term default action is to terminate the process. .ip ign default action is to ignore the signal. .ip core default action is to terminate the process and dump core (see .br core (5)). .ip stop default action is to stop the process. .ip cont default action is to continue the process if it is currently stopped. .pp a process can change the disposition of a signal using .br sigaction (2) or .br signal (2). (the latter is less portable when establishing a signal handler; see .br signal (2) for details.) using these system calls, a process can elect one of the following behaviors to occur on delivery of the signal: perform the default action; ignore the signal; or catch the signal with a .ir "signal handler" , a programmer-defined function that is automatically invoked when the signal is delivered. .pp by default, a signal handler is invoked on the normal process stack. it is possible to arrange that the signal handler uses an alternate stack; see .br sigaltstack (2) for a discussion of how to do this and when it might be useful. .pp the signal disposition is a per-process attribute: in a multithreaded application, the disposition of a particular signal is the same for all threads. .pp a child created via .br fork (2) inherits a copy of its parent's signal dispositions. during an .br execve (2), the dispositions of handled signals are reset to the default; the dispositions of ignored signals are left unchanged. .ss sending a signal the following system calls and library functions allow the caller to send a signal: .tp .br raise (3) sends a signal to the calling thread. .tp .br kill (2) sends a signal to a specified process, to all members of a specified process group, or to all processes on the system. .tp .br pidfd_send_signal (2) sends a signal to a process identified by a pid file descriptor. .tp .br killpg (3) sends a signal to all of the members of a specified process group. .tp .br pthread_kill (3) sends a signal to a specified posix thread in the same process as the caller. .tp .br tgkill (2) sends a signal to a specified thread within a specific process. (this is the system call used to implement .br pthread_kill (3).) .tp .br sigqueue (3) sends a real-time signal with accompanying data to a specified process. .ss waiting for a signal to be caught the following system calls suspend execution of the calling thread until a signal is caught (or an unhandled signal terminates the process): .tp .br pause (2) suspends execution until any signal is caught. .tp .br sigsuspend (2) temporarily changes the signal mask (see below) and suspends execution until one of the unmasked signals is caught. .\" .ss synchronously accepting a signal rather than asynchronously catching a signal via a signal handler, it is possible to synchronously accept the signal, that is, to block execution until the signal is delivered, at which point the kernel returns information about the signal to the caller. there are two general ways to do this: .ip * 2 .br sigwaitinfo (2), .br sigtimedwait (2), and .br sigwait (3) suspend execution until one of the signals in a specified set is delivered. each of these calls returns information about the delivered signal. .ip * .br signalfd (2) returns a file descriptor that can be used to read information about signals that are delivered to the caller. each .br read (2) from this file descriptor blocks until one of the signals in the set specified in the .br signalfd (2) call is delivered to the caller. the buffer returned by .br read (2) contains a structure describing the signal. .ss signal mask and pending signals a signal may be .ir blocked , which means that it will not be delivered until it is later unblocked. between the time when it is generated and when it is delivered a signal is said to be .ir pending . .pp each thread in a process has an independent .ir "signal mask" , which indicates the set of signals that the thread is currently blocking. a thread can manipulate its signal mask using .br pthread_sigmask (3). in a traditional single-threaded application, .br sigprocmask (2) can be used to manipulate the signal mask. .pp a child created via .br fork (2) inherits a copy of its parent's signal mask; the signal mask is preserved across .br execve (2). .pp a signal may be process-directed or thread-directed. a process-directed signal is one that is targeted at (and thus pending for) the process as a whole. a signal may be process-directed because it was generated by the kernel for reasons other than a hardware exception, or because it was sent using .br kill (2) or .br sigqueue (3). a thread-directed signal is one that is targeted at a specific thread. a signal may be thread-directed because it was generated as a consequence of executing a specific machine-language instruction that triggered a hardware exception (e.g., .b sigsegv for an invalid memory access, or .b sigfpe for a math error), or because it was targeted at a specific thread using interfaces such as .br tgkill (2) or .br pthread_kill (3). .pp a process-directed signal may be delivered to any one of the threads that does not currently have the signal blocked. .\" joseph c. sible notes: .\" on linux, if the main thread has the signal unblocked, then the kernel .\" will always deliver the signal there, citing this kernel code .\" .\" per this comment in kernel/signal.c since time immemorial: .\" .\" /* .\" * now find a thread we can wake up to take the signal off the queue. .\" * .\" * if the main thread wants the signal, it gets first crack. .\" * probably the least surprising to the average bear. .\" */ .\" .\" but this does not mean the signal will be delivered only in the .\" main thread, since if a handler is already executing in the main thread .\" (and thus the signal is blocked in that thread), then a further .\" might be delivered in a different thread. .\" if more than one of the threads has the signal unblocked, then the kernel chooses an arbitrary thread to which to deliver the signal. .pp a thread can obtain the set of signals that it currently has pending using .br sigpending (2). this set will consist of the union of the set of pending process-directed signals and the set of signals pending for the calling thread. .pp a child created via .br fork (2) initially has an empty pending signal set; the pending signal set is preserved across an .br execve (2). .\" .ss execution of signal handlers whenever there is a transition from kernel-mode to user-mode execution (e.g., on return from a system call or scheduling of a thread onto the cpu), the kernel checks whether there is a pending unblocked signal for which the process has established a signal handler. if there is such a pending signal, the following steps occur: .ip 1. 3 the kernel performs the necessary preparatory steps for execution of the signal handler: .rs .ip a) 3 the signal is removed from the set of pending signals. .ip b) if the signal handler was installed by a call to .br sigaction (2) that specified the .br sa_onstack flag and the thread has defined an alternate signal stack (using .br sigaltstack (2)), then that stack is installed. .ip c) various pieces of signal-related context are saved into a special frame that is created on the stack. the saved information includes: .rs .ip + 2 the program counter register (i.e., the address of the next instruction in the main program that should be executed when the signal handler returns); .ip + architecture-specific register state required for resuming the interrupted program; .ip + the thread's current signal mask; .ip + the thread's alternate signal stack settings. .re .ip (if the signal handler was installed using the .br sigaction (2) .b sa_siginfo flag, then the above information is accessible via the .i ucontext_t object that is pointed to by the third argument of the signal handler.) .ip d) any signals specified in .i act\->sa_mask when registering the handler with .br sigprocmask (2) are added to the thread's signal mask. the signal being delivered is also added to the signal mask, unless .b sa_nodefer was specified when registering the handler. these signals are thus blocked while the handler executes. .re .ip 2. the kernel constructs a frame for the signal handler on the stack. the kernel sets the program counter for the thread to point to the first instruction of the signal handler function, and configures the return address for that function to point to a piece of user-space code known as the signal trampoline (described in .br sigreturn (2)). .ip 3. the kernel passes control back to user-space, where execution commences at the start of the signal handler function. .ip 4. when the signal handler returns, control passes to the signal trampoline code. .ip 5. the signal trampoline calls .br sigreturn (2), a system call that uses the information in the stack frame created in step 1 to restore the thread to its state before the signal handler was called. the thread's signal mask and alternate signal stack settings are restored as part of this procedure. upon completion of the call to .br sigreturn (2), the kernel transfers control back to user space, and the thread recommences execution at the point where it was interrupted by the signal handler. .pp note that if the signal handler does not return (e.g., control is transferred out of the handler using .br siglongjmp (3), or the handler executes a new program with .br execve (2)), then the final step is not performed. in particular, in such scenarios it is the programmer's responsibility to restore the state of the signal mask (using .br sigprocmask (2)), if it is desired to unblock the signals that were blocked on entry to the signal handler. (note that .br siglongjmp (3) may or may not restore the signal mask, depending on the .i savesigs value that was specified in the corresponding call to .br sigsetjmp (3).) .pp from the kernel's point of view, execution of the signal handler code is exactly the same as the execution of any other user-space code. that is to say, the kernel does not record any special state information indicating that the thread is currently executing inside a signal handler. all necessary state information is maintained in user-space registers and the user-space stack. the depth to which nested signal handlers may be invoked is thus limited only by the user-space stack (and sensible software design!). .\" .ss standard signals linux supports the standard signals listed below. the second column of the table indicates which standard (if any) specified the signal: "p1990" indicates that the signal is described in the original posix.1-1990 standard; "p2001" indicates that the signal was added in susv2 and posix.1-2001. .ts l c c l ____ lb c c l. signal standard action comment sigabrt p1990 core abort signal from \fbabort\fp(3) sigalrm p1990 term timer signal from \fbalarm\fp(2) sigbus p2001 core bus error (bad memory access) sigchld p1990 ign child stopped or terminated sigcld \- ign a synonym for \fbsigchld\fp sigcont p1990 cont continue if stopped sigemt \- term emulator trap sigfpe p1990 core floating-point exception sighup p1990 term hangup detected on controlling terminal or death of controlling process sigill p1990 core illegal instruction siginfo \- a synonym for \fbsigpwr\fp sigint p1990 term interrupt from keyboard sigio \- term i/o now possible (4.2bsd) sigiot \- core iot trap. a synonym for \fbsigabrt\fp sigkill p1990 term kill signal siglost \- term file lock lost (unused) sigpipe p1990 term broken pipe: write to pipe with no readers; see \fbpipe\fp(7) sigpoll p2001 term pollable event (sys v); synonym for \fbsigio\fp sigprof p2001 term profiling timer expired sigpwr \- term power failure (system v) sigquit p1990 core quit from keyboard sigsegv p1990 core invalid memory reference sigstkflt \- term stack fault on coprocessor (unused) sigstop p1990 stop stop process sigtstp p1990 stop stop typed at terminal sigsys p2001 core bad system call (svr4); see also \fbseccomp\fp(2) sigterm p1990 term termination signal sigtrap p2001 core trace/breakpoint trap sigttin p1990 stop terminal input for background process sigttou p1990 stop terminal output for background process sigunused \- core synonymous with \fbsigsys\fp sigurg p2001 ign urgent condition on socket (4.2bsd) sigusr1 p1990 term user-defined signal 1 sigusr2 p1990 term user-defined signal 2 sigvtalrm p2001 term virtual alarm clock (4.2bsd) sigxcpu p2001 core cpu time limit exceeded (4.2bsd); see \fbsetrlimit\fp(2) sigxfsz p2001 core file size limit exceeded (4.2bsd); see \fbsetrlimit\fp(2) sigwinch \- ign window resize signal (4.3bsd, sun) .te .pp the signals .b sigkill and .b sigstop cannot be caught, blocked, or ignored. .pp up to and including linux 2.2, the default behavior for .br sigsys ", " sigxcpu ", " sigxfsz , and (on architectures other than sparc and mips) .b sigbus was to terminate the process (without a core dump). (on some other unix systems the default action for .br sigxcpu " and " sigxfsz is to terminate the process without a core dump.) linux 2.4 conforms to the posix.1-2001 requirements for these signals, terminating the process with a core dump. .pp .b sigemt is not specified in posix.1-2001, but nevertheless appears on most other unix systems, where its default action is typically to terminate the process with a core dump. .pp .b sigpwr (which is not specified in posix.1-2001) is typically ignored by default on those other unix systems where it appears. .pp .b sigio (which is not specified in posix.1-2001) is ignored by default on several other unix systems. .\" .ss queueing and delivery semantics for standard signals if multiple standard signals are pending for a process, the order in which the signals are delivered is unspecified. .pp standard signals do not queue. if multiple instances of a standard signal are generated while that signal is blocked, then only one instance of the signal is marked as pending (and the signal will be delivered just once when it is unblocked). in the case where a standard signal is already pending, the .i siginfo_t structure (see .br sigaction (2)) associated with that signal is not overwritten on arrival of subsequent instances of the same signal. thus, the process will receive the information associated with the first instance of the signal. .\" .ss signal numbering for standard signals the numeric value for each signal is given in the table below. as shown in the table, many signals have different numeric values on different architectures. the first numeric value in each table row shows the signal number on x86, arm, and most other architectures; the second value is for alpha and sparc; the third is for mips; and the last is for parisc. a dash (\-) denotes that a signal is absent on the corresponding architecture. .ts l c c c c l l c c c c l ______ lb c c c c l. signal x86/arm alpha/ mips parisc notes most others sparc sighup \01 \01 \01 \01 sigint \02 \02 \02 \02 sigquit \03 \03 \03 \03 sigill \04 \04 \04 \04 sigtrap \05 \05 \05 \05 sigabrt \06 \06 \06 \06 sigiot \06 \06 \06 \06 sigbus \07 10 10 10 sigemt \- \07 \07 - sigfpe \08 \08 \08 \08 sigkill \09 \09 \09 \09 sigusr1 10 30 16 16 sigsegv 11 11 11 11 sigusr2 12 31 17 17 sigpipe 13 13 13 13 sigalrm 14 14 14 14 sigterm 15 15 15 15 sigstkflt 16 \- \- \07 sigchld 17 20 18 18 sigcld \- \- 18 \- sigcont 18 19 25 26 sigstop 19 17 23 24 sigtstp 20 18 24 25 sigttin 21 21 26 27 sigttou 22 22 27 28 sigurg 23 16 21 29 sigxcpu 24 24 30 12 sigxfsz 25 25 31 30 sigvtalrm 26 26 28 20 sigprof 27 27 29 21 sigwinch 28 28 20 23 sigio 29 23 22 22 sigpoll same as sigio sigpwr 30 29/\- 19 19 siginfo \- 29/\- \- \- siglost \- \-/29 \- \- sigsys 31 12 12 31 sigunused 31 \- \- 31 .te .pp note the following: .ip * 3 where defined, .b sigunused is synonymous with .br sigsys . since glibc 2.26, .b sigunused is no longer defined on any architecture. .ip * signal 29 is .br siginfo / sigpwr (synonyms for the same value) on alpha but .b siglost on sparc. .\" .ss real-time signals starting with version 2.2, linux supports real-time signals as originally defined in the posix.1b real-time extensions (and now included in posix.1-2001). the range of supported real-time signals is defined by the macros .b sigrtmin and .br sigrtmax . posix.1-2001 requires that an implementation support at least .b _posix_rtsig_max (8) real-time signals. .pp the linux kernel supports a range of 33 different real-time signals, numbered 32 to 64. however, the glibc posix threads implementation internally uses two (for nptl) or three (for linuxthreads) real-time signals (see .br pthreads (7)), and adjusts the value of .b sigrtmin suitably (to 34 or 35). because the range of available real-time signals varies according to the glibc threading implementation (and this variation can occur at run time according to the available kernel and glibc), and indeed the range of real-time signals varies across unix systems, programs should .ir "never refer to real-time signals using hard-coded numbers" , but instead should always refer to real-time signals using the notation .br sigrtmin +n, and include suitable (run-time) checks that .br sigrtmin +n does not exceed .br sigrtmax . .pp unlike standard signals, real-time signals have no predefined meanings: the entire set of real-time signals can be used for application-defined purposes. .pp the default action for an unhandled real-time signal is to terminate the receiving process. .pp real-time signals are distinguished by the following: .ip 1. 4 multiple instances of real-time signals can be queued. by contrast, if multiple instances of a standard signal are delivered while that signal is currently blocked, then only one instance is queued. .ip 2. 4 if the signal is sent using .br sigqueue (3), an accompanying value (either an integer or a pointer) can be sent with the signal. if the receiving process establishes a handler for this signal using the .b sa_siginfo flag to .br sigaction (2), then it can obtain this data via the .i si_value field of the .i siginfo_t structure passed as the second argument to the handler. furthermore, the .i si_pid and .i si_uid fields of this structure can be used to obtain the pid and real user id of the process sending the signal. .ip 3. 4 real-time signals are delivered in a guaranteed order. multiple real-time signals of the same type are delivered in the order they were sent. if different real-time signals are sent to a process, they are delivered starting with the lowest-numbered signal. (i.e., low-numbered signals have highest priority.) by contrast, if multiple standard signals are pending for a process, the order in which they are delivered is unspecified. .pp if both standard and real-time signals are pending for a process, posix leaves it unspecified which is delivered first. linux, like many other implementations, gives priority to standard signals in this case. .pp according to posix, an implementation should permit at least .b _posix_sigqueue_max (32) real-time signals to be queued to a process. however, linux does things differently. in kernels up to and including 2.6.7, linux imposes a system-wide limit on the number of queued real-time signals for all processes. this limit can be viewed and (with privilege) changed via the .i /proc/sys/kernel/rtsig\-max file. a related file, .ir /proc/sys/kernel/rtsig\-nr , can be used to find out how many real-time signals are currently queued. in linux 2.6.8, these .i /proc interfaces were replaced by the .b rlimit_sigpending resource limit, which specifies a per-user limit for queued signals; see .br setrlimit (2) for further details. .pp the addition of real-time signals required the widening of the signal set structure .ri ( sigset_t ) from 32 to 64 bits. consequently, various system calls were superseded by new system calls that supported the larger signal sets. the old and new system calls are as follows: .ts lb lb l l. linux 2.0 and earlier linux 2.2 and later \fbsigaction\fp(2) \fbrt_sigaction\fp(2) \fbsigpending\fp(2) \fbrt_sigpending\fp(2) \fbsigprocmask\fp(2) \fbrt_sigprocmask\fp(2) \fbsigreturn\fp(2) \fbrt_sigreturn\fp(2) \fbsigsuspend\fp(2) \fbrt_sigsuspend\fp(2) \fbsigtimedwait\fp(2) \fbrt_sigtimedwait\fp(2) .te .\" .ss interruption of system calls and library functions by signal handlers if a signal handler is invoked while a system call or library function call is blocked, then either: .ip * 2 the call is automatically restarted after the signal handler returns; or .ip * the call fails with the error .br eintr . .pp which of these two behaviors occurs depends on the interface and whether or not the signal handler was established using the .br sa_restart flag (see .br sigaction (2)). the details vary across unix systems; below, the details for linux. .pp if a blocked call to one of the following interfaces is interrupted by a signal handler, then the call is automatically restarted after the signal handler returns if the .br sa_restart flag was used; otherwise the call fails with the error .br eintr : .\" the following system calls use erestartsys, .\" so that they are restartable .ip * 2 .br read (2), .br readv (2), .br write (2), .br writev (2), and .br ioctl (2) calls on "slow" devices. a "slow" device is one where the i/o call may block for an indefinite time, for example, a terminal, pipe, or socket. if an i/o call on a slow device has already transferred some data by the time it is interrupted by a signal handler, then the call will return a success status (normally, the number of bytes transferred). note that a (local) disk is not a slow device according to this definition; i/o operations on disk devices are not interrupted by signals. .ip * .br open (2), if it can block (e.g., when opening a fifo; see .br fifo (7)). .ip * .br wait (2), .br wait3 (2), .br wait4 (2), .br waitid (2), and .br waitpid (2). .ip * socket interfaces: .\" if a timeout (setsockopt()) is in effect on the socket, then these .\" system calls switch to using eintr. consequently, they and are not .\" automatically restarted, and they show the stop/cont behavior .\" described below. (verified from 2.6.26 source, and by experiment; mtk) .br accept (2), .br connect (2), .br recv (2), .br recvfrom (2), .br recvmmsg (2), .br recvmsg (2), .br send (2), .br sendto (2), and .br sendmsg (2), .\" fixme what about sendmmsg()? unless a timeout has been set on the socket (see below). .ip * file locking interfaces: .br flock (2) and the .br f_setlkw and .br f_ofd_setlkw operations of .br fcntl (2) .ip * posix message queue interfaces: .br mq_receive (3), .br mq_timedreceive (3), .br mq_send (3), and .br mq_timedsend (3). .ip * .br futex (2) .b futex_wait (since linux 2.6.22; .\" commit 72c1bbf308c75a136803d2d76d0e18258be14c7a beforehand, always failed with .br eintr ). .ip * .br getrandom (2). .ip * .br pthread_mutex_lock (3), .br pthread_cond_wait (3), and related apis. .ip * .br futex (2) .br futex_wait_bitset . .ip * posix semaphore interfaces: .br sem_wait (3) and .br sem_timedwait (3) (since linux 2.6.22; .\" as a consequence of the 2.6.22 changes in the futex() implementation beforehand, always failed with .br eintr ). .ip * .br read (2) from an .br inotify (7) file descriptor (since linux 3.8; .\" commit 1ca39ab9d21ac93f94b9e3eb364ea9a5cf2aba06 beforehand, always failed with .br eintr ). .pp the following interfaces are never restarted after being interrupted by a signal handler, regardless of the use of .br sa_restart ; they always fail with the error .b eintr when interrupted by a signal handler: .\" these are the system calls that give eintr or erestartnohand .\" on interruption by a signal handler. .ip * 2 "input" socket interfaces, when a timeout .rb ( so_rcvtimeo ) has been set on the socket using .br setsockopt (2): .br accept (2), .br recv (2), .br recvfrom (2), .br recvmmsg (2) (also with a non-null .ir timeout argument), and .br recvmsg (2). .ip * "output" socket interfaces, when a timeout .rb ( so_rcvtimeo ) has been set on the socket using .br setsockopt (2): .br connect (2), .br send (2), .br sendto (2), and .br sendmsg (2). .\" fixme what about sendmmsg()? .ip * interfaces used to wait for signals: .br pause (2), .br sigsuspend (2), .br sigtimedwait (2), and .br sigwaitinfo (2). .ip * file descriptor multiplexing interfaces: .br epoll_wait (2), .br epoll_pwait (2), .br poll (2), .br ppoll (2), .br select (2), and .br pselect (2). .ip * system v ipc interfaces: .\" on some other systems, sa_restart does restart these system calls .br msgrcv (2), .br msgsnd (2), .br semop (2), and .br semtimedop (2). .ip * sleep interfaces: .br clock_nanosleep (2), .br nanosleep (2), and .br usleep (3). .ip * .br io_getevents (2). .pp the .br sleep (3) function is also never restarted if interrupted by a handler, but gives a success return: the number of seconds remaining to sleep. .pp in certain circumstances, the .br seccomp (2) user-space notification feature can lead to restarting of system calls that would otherwise never be restarted by .br sa_restart ; for details, see .br seccomp_unotify (2). .\" .ss interruption of system calls and library functions by stop signals on linux, even in the absence of signal handlers, certain blocking interfaces can fail with the error .br eintr after the process is stopped by one of the stop signals and then resumed via .br sigcont . this behavior is not sanctioned by posix.1, and doesn't occur on other systems. .pp the linux interfaces that display this behavior are: .ip * 2 "input" socket interfaces, when a timeout .rb ( so_rcvtimeo ) has been set on the socket using .br setsockopt (2): .br accept (2), .br recv (2), .br recvfrom (2), .br recvmmsg (2) (also with a non-null .ir timeout argument), and .br recvmsg (2). .ip * "output" socket interfaces, when a timeout .rb ( so_rcvtimeo ) has been set on the socket using .br setsockopt (2): .br connect (2), .br send (2), .br sendto (2), and .\" fixme what about sendmmsg()? .br sendmsg (2), if a send timeout .rb ( so_sndtimeo ) has been set. .ip * 2 .br epoll_wait (2), .br epoll_pwait (2). .ip * .br semop (2), .br semtimedop (2). .ip * .br sigtimedwait (2), .br sigwaitinfo (2). .ip * linux 3.7 and earlier: .br read (2) from an .br inotify (7) file descriptor .\" commit 1ca39ab9d21ac93f94b9e3eb364ea9a5cf2aba06 .ip * linux 2.6.21 and earlier: .br futex (2) .br futex_wait , .br sem_timedwait (3), .br sem_wait (3). .ip * linux 2.6.8 and earlier: .br msgrcv (2), .br msgsnd (2). .ip * linux 2.4 and earlier: .br nanosleep (2). .sh conforming to posix.1, except as noted. .sh notes for a discussion of async-signal-safe functions, see .br signal\-safety (7). .pp the .i /proc/[pid]/task/[tid]/status file contains various fields that show the signals that a thread is blocking .ri ( sigblk ), catching .ri ( sigcgt ), or ignoring .ri ( sigign ). (the set of signals that are caught or ignored will be the same across all threads in a process.) other fields show the set of pending signals that are directed to the thread .ri ( sigpnd ) as well as the set of pending signals that are directed to the process as a whole .ri ( shdpnd ). the corresponding fields in .i /proc/[pid]/status show the information for the main thread. see .br proc (5) for further details. .sh bugs there are six signals that can be delivered as a consequence of a hardware exception: .br sigbus , .br sigemt , .br sigfpe , .br sigill , .br sigsegv , and .br sigtrap . which of these signals is delivered, for any given hardware exception, is not documented and does not always make sense. .pp for example, an invalid memory access that causes delivery of .b sigsegv on one cpu architecture may cause delivery of .b sigbus on another architecture, or vice versa. .pp for another example, using the x86 .i int instruction with a forbidden argument (any number other than 3 or 128) causes delivery of .br sigsegv , even though .b sigill would make more sense, because of how the cpu reports the forbidden operation to the kernel. .sh see also .br kill (1), .br clone (2), .br getrlimit (2), .br kill (2), .br pidfd_send_signal (2), .br restart_syscall (2), .br rt_sigqueueinfo (2), .br setitimer (2), .br setrlimit (2), .br sgetmask (2), .br sigaction (2), .br sigaltstack (2), .br signal (2), .br signalfd (2), .br sigpending (2), .br sigprocmask (2), .br sigreturn (2), .br sigsuspend (2), .br sigwaitinfo (2), .br abort (3), .br bsd_signal (3), .br killpg (3), .br longjmp (3), .br pthread_sigqueue (3), .br raise (3), .br sigqueue (3), .br sigset (3), .br sigsetops (3), .br sigvec (3), .br sigwait (3), .br strsignal (3), .br swapcontext (3), .br sysv_signal (3), .br core (5), .br proc (5), .br nptl (7), .br pthreads (7), .br sigevent (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2008 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_attr_setschedpolicy 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_attr_setschedpolicy, pthread_attr_getschedpolicy \- set/get scheduling policy attribute in thread attributes object .sh synopsis .nf .b #include .pp .bi "int pthread_attr_setschedpolicy(pthread_attr_t *" attr ", int " policy ); .bi "int pthread_attr_getschedpolicy(const pthread_attr_t *restrict " attr , .bi " int *restrict " policy ); .pp compile and link with \fi\-pthread\fp. .fi .sh description the .br pthread_attr_setschedpolicy () function sets the scheduling policy attribute of the thread attributes object referred to by .ir attr to the value specified in .ir policy . this attribute determines the scheduling policy of a thread created using the thread attributes object .ir attr . .pp the supported values for .i policy are .br sched_fifo , .br sched_rr , and .br sched_other , with the semantics described in .br sched (7). .\" fixme . pthread_setschedparam() places no restriction on the policy, .\" but pthread_attr_setschedpolicy() restricts policy to rr/fifo/other .\" http://sourceware.org/bugzilla/show_bug.cgi?id=7013 .pp the .br pthread_attr_getschedpolicy () returns the scheduling policy attribute of the thread attributes object .ir attr in the buffer pointed to by .ir policy . .pp in order for the policy setting made by .br pthread_attr_setschedpolicy () to have effect when calling .br pthread_create (3), the caller must use .br pthread_attr_setinheritsched (3) to set the inherit-scheduler attribute of the attributes object .i attr to .br pthread_explicit_sched . .sh return value on success, these functions return 0; on error, they return a nonzero error number. .sh errors .br pthread_attr_setschedpolicy () can fail with the following error: .tp .b einval invalid value in .ir policy . .pp posix.1 also documents an optional .b enotsup error ("attempt was made to set the attribute to an unsupported value") for .br pthread_attr_setschedpolicy (). .\" .sh versions .\" available since glibc 2.0. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_attr_setschedpolicy (), .br pthread_attr_getschedpolicy () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh examples see .br pthread_setschedparam (3). .sh see also .ad l .nh .br pthread_attr_init (3), .br pthread_attr_setinheritsched (3), .br pthread_attr_setschedparam (3), .br pthread_create (3), .br pthread_setschedparam (3), .br pthread_setschedprio (3), .br pthreads (7), .br sched (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/unlocked_stdio.3 .so man2/pkey_alloc.2 .\" manpage for /etc/dir_colors, config file for dircolors(1) .\" extracted from color-ls 3.12.0.3 dircolors(1) manpage .\" .\" %%%license_start(ldpv1) .\" this file may be copied under the conditions described .\" in the ldp general public license, version 1, september 1998 .\" that should have been distributed together with this file. .\" %%%license_end .\" .\" modified sat dec 22 22:25:33 2001 by martin schulze .\" .th dir_colors 5 2020-08-13 "gnu" "linux user manual" .sh name dir_colors \- configuration file for dircolors(1) .sh description the program .br ls (1) uses the environment variable .b ls_colors to determine the colors in which the filenames are to be displayed. this environment variable is usually set by a command like .pp .rs eval \`dircolors some_path/dir_colors\` .re .pp found in a system default shell initialization file, like .i /etc/profile or .ir /etc/csh.cshrc . (see also .br dircolors (1).) usually, the file used here is .i /etc/dir_colors and can be overridden by a .i .dir_colors file in one's home directory. .pp this configuration file consists of several statements, one per line. anything right of a hash mark (#) is treated as a comment, if the hash mark is at the beginning of a line or is preceded by at least one whitespace. blank lines are ignored. .pp the .i global section of the file consists of any statement before the first .b term statement. any statement in the global section of the file is considered valid for all terminal types. following the global section is one or more .i terminal-specific sections, preceded by one or more .b term statements which specify the terminal types (as given by the .b term environment variable) the following declarations apply to. it is always possible to override a global declaration by a subsequent terminal-specific one. .pp the following statements are recognized; case is insignificant: .tp .b term \fiterminal-type\fr starts a terminal-specific section and specifies which terminal it applies to. multiple .b term statements can be used to create a section which applies for several terminal types. .tp .b color yes|all|no|none|tty (slackware only; ignored by gnu .br dircolors (1).) specifies that colorization should always be enabled (\fiyes\fr or \fiall\fr), never enabled (\fino\fr or \finone\fr), or enabled only if the output is a terminal (\fitty\fr). the default is \fino\fr. .tp .b eightbit yes|no (slackware only; ignored by gnu .br dircolors (1).) specifies that eight-bit iso 8859 characters should be enabled by default. for compatibility reasons, this can also be specified as 1 for \fiyes\fr or 0 for \fino\fr. the default is \fino\fr. .tp .b options \fioptions\fr (slackware only; ignored by gnu .br dircolors (1).) adds command-line options to the default .b ls command line. the options can be any valid .b ls command-line options, and should include the leading minus sign. note that .b dircolors does not verify the validity of these options. .tp .b normal \ficolor-sequence\fr specifies the color used for normal (nonfilename) text. .ip synonym: .br norm . .tp .b file \ficolor-sequence\fr specifies the color used for a regular file. .tp .b dir \ficolor-sequence\fr specifies the color used for directories. .tp .b link \ficolor-sequence\fr specifies the color used for a symbolic link. .ip synonyms: .br lnk , .br symlink . .tp .b orphan \ficolor-sequence\fr specifies the color used for an orphaned symbolic link (one which points to a nonexistent file). if this is unspecified, .b ls will use the .b link color instead. .tp .b missing \ficolor-sequence\fr specifies the color used for a missing file (a nonexistent file which nevertheless has a symbolic link pointing to it). if this is unspecified, .b ls will use the .b file color instead. .tp .b fifo \ficolor-sequence\fr specifies the color used for a fifo (named pipe). .ip synonym: .br pipe . .tp .b sock \ficolor-sequence\fr specifies the color used for a socket. .tp .b door \ficolor-sequence\fr (supported since fileutils 4.1) specifies the color used for a door (solaris 2.5 and later). .tp .b blk \ficolor-sequence\fr specifies the color used for a block device special file. .ip synonym: .br block . .tp .b chr \ficolor-sequence\fr specifies the color used for a character device special file. .ip synonym: .br char . .tp .b exec \ficolor-sequence\fr specifies the color used for a file with the executable attribute set. .tp .b suid \ficolor-sequence\fr specifies the color used for a file with the set-user-id attribute set. .ip synonym: .br setuid . .tp .b sgid \ficolor-sequence\fr specifies the color used for a file with the set-group-id attribute set. .ip synonym: .br setgid . .tp .b sticky \ficolor-sequence\fr specifies the color used for a directory with the sticky attribute set. .tp .b sticky_other_writable \ficolor-sequence\fr specifies the color used for an other-writable directory with the executable attribute set. .ip synonym: .br owt . .tp .b other_writable \ficolor-sequence\fr specifies the color used for an other-writable directory without the executable attribute set. .ip synonym: .br owr . .tp .b leftcode \ficolor-sequence\fr specifies the .i "left code" for non-iso\ 6429 terminals (see below). .ip synonym: .br left . .tp .b rightcode \ficolor-sequence\fr specifies the .i "right code" for non-iso\ 6429 terminals (see below). .ip synonym: .br right . .tp .b endcode \ficolor-sequence\fr specifies the .i "end code" for non-iso\ 6429 terminals (see below). .ip synonym: .br end . .tp \fb*\fiextension\fr \ficolor-sequence\fr specifies the color used for any file that ends in \fiextension\fr. .tp \fb .\fiextension\fr \ficolor-sequence\fr same as \fb*\fr.\fiextension\fr. specifies the color used for any file that ends in .\fiextension\fr. note that the period is included in the extension, which makes it impossible to specify an extension not starting with a period, such as .b \(ti for .b emacs backup files. this form should be considered obsolete. .ss iso 6429 (ansi) color sequences most color-capable ascii terminals today use iso 6429 (ansi) color sequences, and many common terminals without color capability, including .b xterm and the widely used and cloned dec vt100, will recognize iso 6429 color codes and harmlessly eliminate them from the output or emulate them. .b ls uses iso 6429 codes by default, assuming colorization is enabled. .pp iso 6429 color sequences are composed of sequences of numbers separated by semicolons. the most common codes are: .rs .ts l l. 0 to restore default color 1 for brighter colors 4 for underlined text 5 for flashing text 30 for black foreground 31 for red foreground 32 for green foreground 33 for yellow (or brown) foreground 34 for blue foreground 35 for purple foreground 36 for cyan foreground 37 for white (or gray) foreground 40 for black background 41 for red background 42 for green background 43 for yellow (or brown) background 44 for blue background 45 for purple background 46 for cyan background 47 for white (or gray) background .te .re .pp not all commands will work on all systems or display devices. .pp .b ls uses the following defaults: .ts lb l l. normal 0 normal (nonfilename) text file 0 regular file dir 32 directory link 36 symbolic link orphan undefined orphaned symbolic link missing undefined missing file fifo 31 named pipe (fifo) sock 33 socket blk 44;37 block device chr 44;37 character device exec 35 executable file .te .pp a few terminal programs do not recognize the default properly. if all text gets colorized after you do a directory listing, change the .b normal and .b file codes to the numerical codes for your normal foreground and background colors. .ss other terminal types (advanced configuration) if you have a color-capable (or otherwise highlighting) terminal (or printer!) which uses a different set of codes, you can still generate a suitable setup. to do so, you will have to use the .br leftcode , .br rightcode , and .b endcode definitions. .pp when writing out a filename, .b ls generates the following output sequence: .b leftcode .i typecode .b rightcode .i filename .br endcode , where the .i typecode is the color sequence that depends on the type or name of file. if the .b endcode is undefined, the sequence .b "leftcode normal rightcode" will be used instead. the purpose of the left- and rightcodes is merely to reduce the amount of typing necessary (and to hide ugly escape codes away from the user). if they are not appropriate for your terminal, you can eliminate them by specifying the respective keyword on a line by itself. .pp .b note: if the .b endcode is defined in the global section of the setup file, it .i cannot be undefined in a terminal-specific section of the file. this means any .b normal definition will have no effect. a different .b endcode can, however, be specified, which would have the same effect. .ss escape sequences to specify control- or blank characters in the color sequences or filename extensions, either c-style \e-escaped notation or .br stty \-style \(ha-notation can be used. the c-style notation includes the following characters: .rs .ts lb l. \ea bell (ascii 7) \eb backspace (ascii 8) \ee escape (ascii 27) \ef form feed (ascii 12) \en newline (ascii 10) \er carriage return (ascii 13) \et tab (ascii 9) \ev vertical tab (ascii 11) \e? delete (ascii 127) \e\finnn any character (octal notation) \ex\finnn any character (hexadecimal notation) \e_ space \e\e backslash (\e) \e\(ha caret (\(ha) \e# hash mark (#) .te .re .pp note that escapes are necessary to enter a space, backslash, caret, or any control character anywhere in the string, as well as a hash mark as the first character. .sh files .tp .i /etc/dir_colors system-wide configuration file. .tp .i \(ti/.dir_colors per-user configuration file. .pp this page describes the .b dir_colors file format as used in the fileutils-4.1 package; other versions may differ slightly. .sh notes the default .b leftcode and .b rightcode definitions, which are used by iso 6429 terminals are: .rs .ts lb l. leftcode \ee[ rightcode m .te .re .pp the default .b endcode is undefined. .sh see also .br dircolors (1), .br ls (1), .br stty (1), .br xterm (1) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/getrlimit.2 .so man3/ldexp.3 .\" copyright (c) 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sat jul 24 18:48:06 1993 by rik faith (faith@cs.unc.edu) .\" modified fri jun 23 01:26:34 1995 by andries brouwer (aeb@cwi.nl) .\" (prompted by scott burkett ) .\" modified sun mar 28 23:44:38 1999 by andries brouwer (aeb@cwi.nl) .\" .th mktemp 3 2021-03-22 "gnu" "linux programmer's manual" .sh name mktemp \- make a unique temporary filename .sh synopsis .nf .b #include .pp .bi "char *mktemp(char *" template ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br mktemp (): .nf since glibc 2.12: (_xopen_source >= 500) && ! (_posix_c_source >= 200112l) || /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _svid_source || _bsd_source before glibc 2.12: _bsd_source || _svid_source || _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended .fi .sh description .ir "never use this function" ; see bugs. .pp the .br mktemp () function generates a unique temporary filename from \fitemplate\fp. the last six characters of \fitemplate\fp must be xxxxxx and these are replaced with a string that makes the filename unique. since it will be modified, .i template must not be a string constant, but should be declared as a character array. .sh return value the .br mktemp () function always returns \fitemplate\fp. if a unique name was created, the last six bytes of \fitemplate\fp will have been modified in such a way that the resulting name is unique (i.e., does not exist already) if a unique name could not be created, \fitemplate\fp is made an empty string, and .i errno is set to indicate the error. .sh errors .tp .b einval the last six characters of \fitemplate\fp were not xxxxxx. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br mktemp () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to 4.3bsd, posix.1-2001. posix.1-2008 removes the specification of .br mktemp (). .\" .sh notes .\" the prototype is in .\" .i .\" for libc4, libc5, glibc1; glibc2 follows the single unix specification .\" and has the prototype in .\" .ir . .sh bugs never use .br mktemp (). some implementations follow 4.3bsd and replace xxxxxx by the current process id and a single letter, so that at most 26 different names can be returned. since on the one hand the names are easy to guess, and on the other hand there is a race between testing whether the name exists and opening the file, every use of .br mktemp () is a security risk. the race is avoided by .br mkstemp (3) and .br mkdtemp (3). .sh see also .br mktemp (1), .br mkdtemp (3), .br mkstemp (3), .br tempnam (3), .br tmpfile (3), .br tmpnam (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/ctanh.3 .\" copyright 1995 robert k. nichols (robert.k.nichols@att.com) .\" copyright 1999-2005 kai mäkisara (kai.makisara@kolumbus.fi) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .th st 4 2020-04-11 "linux" "linux programmer's manual" .sh name st \- scsi tape device .sh synopsis .nf .b #include .pp .bi "int ioctl(int " fd ", int " request " [, (void *)" arg3 "]);" .bi "int ioctl(int " fd ", mtioctop, (struct mtop *)" mt_cmd ); .bi "int ioctl(int " fd ", mtiocget, (struct mtget *)" mt_status ); .bi "int ioctl(int " fd ", mtiocpos, (struct mtpos *)" mt_pos ); .fi .sh description the .b st driver provides the interface to a variety of scsi tape devices. currently, the driver takes control of all detected devices of type \(lqsequential-access\(rq. the .b st driver uses major device number 9. .pp each device uses eight minor device numbers. the lowermost five bits in the minor numbers are assigned sequentially in the order of detection. in the 2.6 kernel, the bits above the eight lowermost bits are concatenated to the five lowermost bits to form the tape number. the minor numbers can be grouped into two sets of four numbers: the principal (auto-rewind) minor device numbers, .ir n , and the \(lqno-rewind\(rq device numbers, .ri ( n " + 128)." devices opened using the principal device number will be sent a .br rewind command when they are closed. devices opened using the \(lqno-rewind\(rq device number will not. (note that using an auto-rewind device for positioning the tape with, for instance, mt does not lead to the desired result: the tape is rewound after the mt command and the next command starts from the beginning of the tape). .pp within each group, four minor numbers are available to define devices with different characteristics (block size, compression, density, etc.) when the system starts up, only the first device is available. the other three are activated when the default characteristics are defined (see below). (by changing compile-time constants, it is possible to change the balance between the maximum number of tape drives and the number of minor numbers for each drive. the default allocation allows control of 32 tape drives. for instance, it is possible to control up to 64 tape drives with two minor numbers for different options.) .pp devices are typically created by: .pp .in +4n .ex mknod \-m 666 /dev/st0 c 9 0 mknod \-m 666 /dev/st0l c 9 32 mknod \-m 666 /dev/st0m c 9 64 mknod \-m 666 /dev/st0a c 9 96 mknod \-m 666 /dev/nst0 c 9 128 mknod \-m 666 /dev/nst0l c 9 160 mknod \-m 666 /dev/nst0m c 9 192 mknod \-m 666 /dev/nst0a c 9 224 .ee .in .pp there is no corresponding block device. .pp the driver uses an internal buffer that has to be large enough to hold at least one tape block. in kernels before 2.1.121, the buffer is allocated as one contiguous block. this limits the block size to the largest contiguous block of memory the kernel allocator can provide. the limit is currently 128\ kb for 32-bit architectures and 256\ kb for 64-bit architectures. in newer kernels the driver allocates the buffer in several parts if necessary. by default, the maximum number of parts is 16. this means that the maximum block size is very large (2\ mb if allocation of 16 blocks of 128\ kb succeeds). .pp the driver's internal buffer size is determined by a compile-time constant which can be overridden with a kernel startup option. in addition to this, the driver tries to allocate a larger temporary buffer at run time if necessary. however, run-time allocation of large contiguous blocks of memory may fail and it is advisable not to rely too much on dynamic buffer allocation with kernels older than 2.1.121 (this applies also to demand-loading the driver with kerneld or kmod). .pp the driver does not specifically support any tape drive brand or model. after system start-up the tape device options are defined by the drive firmware. for example, if the drive firmware selects fixed-block mode, the tape device uses fixed-block mode. the options can be changed with explicit .br ioctl (2) calls and remain in effect when the device is closed and reopened. setting the options affects both the auto-rewind and the nonrewind device. .pp different options can be specified for the different devices within the subgroup of four. the options take effect when the device is opened. for example, the system administrator can define one device that writes in fixed-block mode with a certain block size, and one which writes in variable-block mode (if the drive supports both modes). .pp the driver supports .b tape partitions if they are supported by the drive. (note that the tape partitions have nothing to do with disk partitions. a partitioned tape can be seen as several logical tapes within one medium.) partition support has to be enabled with an .br ioctl (2). the tape location is preserved within each partition across partition changes. the partition used for subsequent tape operations is selected with an .br ioctl (2). the partition switch is executed together with the next tape operation in order to avoid unnecessary tape movement. the maximum number of partitions on a tape is defined by a compile-time constant (originally four). the driver contains an .br ioctl (2) that can format a tape with either one or two partitions. .pp device .i /dev/tape is usually created as a hard or soft link to the default tape device on the system. .pp starting from kernel 2.6.2, the driver exports in the sysfs directory .i /sys/class/scsi_tape the attached devices and some parameters assigned to the devices. .ss data transfer the driver supports operation in both fixed-block mode and variable-block mode (if supported by the drive). in fixed-block mode the drive writes blocks of the specified size and the block size is not dependent on the byte counts of the write system calls. in variable-block mode one tape block is written for each write call and the byte count determines the size of the corresponding tape block. note that the blocks on the tape don't contain any information about the writing mode: when reading, the only important thing is to use commands that accept the block sizes on the tape. .pp in variable-block mode the read byte count does not have to match the tape block size exactly. if the byte count is larger than the next block on tape, the driver returns the data and the function returns the actual block size. if the block size is larger than the byte count, an error is returned. .pp in fixed-block mode the read byte counts can be arbitrary if buffering is enabled, or a multiple of the tape block size if buffering is disabled. kernels before 2.1.121 allow writes with arbitrary byte count if buffering is enabled. in all other cases (kernel before 2.1.121 with buffering disabled or newer kernel) the write byte count must be a multiple of the tape block size. .pp in the 2.6 kernel, the driver tries to use direct transfers between the user buffer and the device. if this is not possible, the driver's internal buffer is used. the reasons for not using direct transfers include improper alignment of the user buffer (default is 512 bytes but this can be changed by the hba driver), one or more pages of the user buffer not reachable by the scsi adapter, and so on. .pp a filemark is automatically written to tape if the last tape operation before close was a write. .pp when a filemark is encountered while reading, the following happens. if there are data remaining in the buffer when the filemark is found, the buffered data is returned. the next read returns zero bytes. the following read returns data from the next file. the end of recorded data is signaled by returning zero bytes for two consecutive read calls. the third read returns an error. .ss ioctls the driver supports three .br ioctl (2) requests. requests not recognized by the .b st driver are passed to the .b scsi driver. the definitions below are from .ir /usr/include/linux/mtio.h : .ss mtioctop \(em perform a tape operation this request takes an argument of type .ir "(struct mtop\ *)" . not all drives support all operations. the driver returns an .b eio error if the drive rejects an operation. .pp .in +4n .ex /* structure for mtioctop \- mag tape op command: */ struct mtop { short mt_op; /* operations defined below */ int mt_count; /* how many of them */ }; .ee .in .pp magnetic tape operations for normal tape use: .tp .b mtbsf backward space over .i mt_count filemarks. .tp .b mtbsfm backward space over .i mt_count filemarks. reposition the tape to the eot side of the last filemark. .tp .b mtbsr backward space over .i mt_count records (tape blocks). .tp .b mtbss backward space over .i mt_count setmarks. .tp .b mtcompression enable compression of tape data within the drive if .i mt_count is nonzero and disable compression if .i mt_count is zero. this command uses the mode page 15 supported by most dats. .tp .b mteom go to the end of the recorded media (for appending files). .tp .b mterase erase tape. with 2.6 kernel, short erase (mark tape empty) is performed if the argument is zero. otherwise, long erase (erase all) is done. .tp .b mtfsf forward space over .i mt_count filemarks. .tp .b mtfsfm forward space over .i mt_count filemarks. reposition the tape to the bot side of the last filemark. .tp .b mtfsr forward space over .i mt_count records (tape blocks). .tp .b mtfss forward space over .i mt_count setmarks. .tp .b mtload execute the scsi load command. a special case is available for some hp autoloaders. if .i mt_count is the constant .b mt_st_hploader_offset plus a number, the number is sent to the drive to control the autoloader. .tp .b mtlock lock the tape drive door. .tp .b mtmkpart format the tape into one or two partitions. if .i mt_count is positive, it gives the size of partition 1 and partition 0 contains the rest of the tape. if .i mt_count is zero, the tape is formatted into one partition. from kernel version 4.6, .\" commit 8038e6456a3e6f5c4759e0d73c4f9165b90c93e7 a negative .i mt_count specifies the size of partition 0 and the rest of the tape contains partition 1. the physical ordering of partitions depends on the drive. this command is not allowed for a drive unless the partition support is enabled for the drive (see .br mt_st_can_partitions below). .tp .b mtnop no op\(emflushes the driver's buffer as a side effect. should be used before reading status with .br mtiocget . .tp .b mtoffl rewind and put the drive off line. .tp .b mtreset reset drive. .tp .b mtreten re-tension tape. .tp .b mtrew rewind. .tp .b mtseek seek to the tape block number specified in .ir mt_count . this operation requires either a scsi-2 drive that supports the .b locate command (device-specific address) or a tandberg-compatible scsi-1 drive (tandberg, archive viper, wangtek, ...). the block number should be one that was previously returned by .br mtiocpos if device-specific addresses are used. .tp .b mtsetblk set the drive's block length to the value specified in .ir mt_count . a block length of zero sets the drive to variable block size mode. .tp .b mtsetdensity set the tape density to the code in .ir mt_count . the density codes supported by a drive can be found from the drive documentation. .tp .b mtsetpart the active partition is switched to .ir mt_count . the partitions are numbered from zero. this command is not allowed for a drive unless the partition support is enabled for the drive (see .b mt_st_can_partitions below). .tp .b mtunload execute the scsi unload command (does not eject the tape). .tp .b mtunlock unlock the tape drive door. .tp .b mtweof write .i mt_count filemarks. .tp .b mtwsm write .i mt_count setmarks. .pp magnetic tape operations for setting of device options (by the superuser): .tp .b mtsetdrvbuffer set various drive and driver options according to bits encoded in .ir mt_count . these consist of the drive's buffering mode, a set of boolean driver options, the buffer write threshold, defaults for the block size and density, and timeouts (only in kernels 2.1 and later). a single operation can affect only one item in the list below (the booleans counted as one item.) .ip a value having zeros in the high-order 4 bits will be used to set the drive's buffering mode. the buffering modes are: .rs 12 .ip 0 4 the drive will not report .br good status on write commands until the data blocks are actually written to the medium. .ip 1 the drive may report .br good status on write commands as soon as all the data has been transferred to the drive's internal buffer. .ip 2 the drive may report .br good status on write commands as soon as (a) all the data has been transferred to the drive's internal buffer, and (b) all buffered data from different initiators has been successfully written to the medium. .re .ip to control the write threshold the value in .i mt_count must include the constant .br mt_st_write_threshold bitwise ored with a block count in the low 28 bits. the block count refers to 1024-byte blocks, not the physical block size on the tape. the threshold cannot exceed the driver's internal buffer size (see description, above). .ip to set and clear the boolean options the value in .i mt_count must include one of the constants .br mt_st_booleans , .br mt_st_setbooleans , .br mt_st_clearbooleans , or .br mt_st_defbooleans bitwise ored with whatever combination of the following options is desired. using .br mt_st_booleans the options can be set to the values defined in the corresponding bits. with .br mt_st_setbooleans the options can be selectively set and with .br mt_st_defbooleans selectively cleared. .ip "" the default options for a tape device are set with .br mt_st_defbooleans . a nonactive tape device (e.g., device with minor 32 or 160) is activated when the default options for it are defined the first time. an activated device inherits from the device activated at start-up the options not set explicitly. .ip "" the boolean options are: .rs .tp .br mt_st_buffer_writes " (default: true)" buffer all write operations in fixed-block mode. if this option is false and the drive uses a fixed block size, then all write operations must be for a multiple of the block size. this option must be set false to write reliable multivolume archives. .tp .br mt_st_async_writes " (default: true)" when this option is true, write operations return immediately without waiting for the data to be transferred to the drive if the data fits into the driver's buffer. the write threshold determines how full the buffer must be before a new scsi write command is issued. any errors reported by the drive will be held until the next operation. this option must be set false to write reliable multivolume archives. .tp .br mt_st_read_ahead " (default: true)" this option causes the driver to provide read buffering and read-ahead in fixed-block mode. if this option is false and the drive uses a fixed block size, then all read operations must be for a multiple of the block size. .tp .br mt_st_two_fm " (default: false)" this option modifies the driver behavior when a file is closed. the normal action is to write a single filemark. if the option is true, the driver will write two filemarks and backspace over the second one. .ip note: this option should not be set true for qic tape drives since they are unable to overwrite a filemark. these drives detect the end of recorded data by testing for blank tape rather than two consecutive filemarks. most other current drives also detect the end of recorded data and using two filemarks is usually necessary only when interchanging tapes with some other systems. .tp .br mt_st_debugging " (default: false)" this option turns on various debugging messages from the driver (effective only if the driver was compiled with .b debug defined nonzero). .tp .br mt_st_fast_eom " (default: false)" this option causes the .b mteom operation to be sent directly to the drive, potentially speeding up the operation but causing the driver to lose track of the current file number normally returned by the .b mtiocget request. if .b mt_st_fast_eom is false, the driver will respond to an .b mteom request by forward spacing over files. .tp .br mt_st_auto_lock " (default: false)" when this option is true, the drive door is locked when the device file is opened and unlocked when it is closed. .tp .br mt_st_def_writes " (default: false)" the tape options (block size, mode, compression, etc.) may change when changing from one device linked to a drive to another device linked to the same drive depending on how the devices are defined. this option defines when the changes are enforced by the driver using scsi-commands and when the drives auto-detection capabilities are relied upon. if this option is false, the driver sends the scsi-commands immediately when the device is changed. if the option is true, the scsi-commands are not sent until a write is requested. in this case, the drive firmware is allowed to detect the tape structure when reading and the scsi-commands are used only to make sure that a tape is written according to the correct specification. .tp .br mt_st_can_bsr " (default: false)" when read-ahead is used, the tape must sometimes be spaced backward to the correct position when the device is closed and the scsi command to space backward over records is used for this purpose. some older drives can't process this command reliably and this option can be used to instruct the driver not to use the command. the end result is that, with read-ahead and fixed-block mode, the tape may not be correctly positioned within a file when the device is closed. with 2.6 kernel, the default is true for drives supporting scsi-3. .tp .br mt_st_no_blklims " (default: false)" some drives don't accept the .b "read block limits" scsi command. if this is used, the driver does not use the command. the drawback is that the driver can't check before sending commands if the selected block size is acceptable to the drive. .tp .br mt_st_can_partitions " (default: false)" this option enables support for several partitions within a tape. the option applies to all devices linked to a drive. .tp .br mt_st_scsi2logical " (default: false)" this option instructs the driver to use the logical block addresses defined in the scsi-2 standard when performing the seek and tell operations (both with .b mtseek and .b mtiocpos commands and when changing tape partition). otherwise, the device-specific addresses are used. it is highly advisable to set this option if the drive supports the logical addresses because they count also filemarks. there are some drives that support only the logical block addresses. .tp .br mt_st_sysv " (default: false)" when this option is enabled, the tape devices use the system v semantics. otherwise, the bsd semantics are used. the most important difference between the semantics is what happens when a device used for reading is closed: in system v semantics the tape is spaced forward past the next filemark if this has not happened while using the device. in bsd semantics the tape position is not changed. .tp .br mt_no_wait " (default: false)" enables immediate mode (i.e., don't wait for the command to finish) for some commands (e.g., rewind). .pp an example: .pp .in +4n .ex struct mtop mt_cmd; mt_cmd.mt_op = mtsetdrvbuffer; mt_cmd.mt_count = mt_st_booleans | mt_st_buffer_writes | mt_st_async_writes; ioctl(fd, mtioctop, mt_cmd); .ee .in .re .ip "" the default block size for a device can be set with .b mt_st_def_blksize and the default density code can be set with .br mt_st_defdensity . the values for the parameters are or'ed with the operation code. .ip "" with kernels 2.1.x and later, the timeout values can be set with the subcommand .b mt_st_set_timeout ored with the timeout in seconds. the long timeout (used for rewinds and other commands that may take a long time) can be set with .br mt_st_set_long_timeout . the kernel defaults are very long to make sure that a successful command is not timed out with any drive. because of this, the driver may seem stuck even if it is only waiting for the timeout. these commands can be used to set more practical values for a specific drive. the timeouts set for one device apply for all devices linked to the same drive. .ip "" starting from kernels 2.4.19 and 2.5.43, the driver supports a status bit which indicates whether the drive requests cleaning. the method used by the drive to return cleaning information is set using the .b mt_st_sel_cln subcommand. if the value is zero, the cleaning bit is always zero. if the value is one, the tapealert data defined in the scsi-3 standard is used (not yet implemented). values 2\(en17 are reserved. if the lowest eight bits are >= 18, bits from the extended sense data are used. the bits 9\(en16 specify a mask to select the bits to look at and the bits 17\(en23 specify the bit pattern to look for. if the bit pattern is zero, one or more bits under the mask indicate the cleaning request. if the pattern is nonzero, the pattern must match the masked sense data byte. .ss mtiocget \(em get status this request takes an argument of type .ir "(struct mtget\ *)" . .pp .in +4n .ex /* structure for mtiocget \- mag tape get status command */ struct mtget { long mt_type; long mt_resid; /* the following registers are device dependent */ long mt_dsreg; long mt_gstat; long mt_erreg; /* the next two fields are not always used */ daddr_t mt_fileno; daddr_t mt_blkno; }; .ee .in .tp \fimt_type\fp the header file defines many values for .ir mt_type , but the current driver reports only the generic types .b mt_isscsi1 (generic scsi-1 tape) and .b mt_isscsi2 (generic scsi-2 tape). .tp \fimt_resid\fp contains the current tape partition number. .tp \fimt_dsreg\fp reports the drive's current settings for block size (in the low 24 bits) and density (in the high 8 bits). these fields are defined by .br mt_st_blksize_shift , .br mt_st_blksize_mask , .br mt_st_density_shift , and .br mt_st_density_mask . .tp \fimt_gstat\fp reports generic (device independent) status information. the header file defines macros for testing these status bits: .rs .hp 4 \fbgmt_eof\fp(\fix\fp): the tape is positioned just after a filemark (always false after an .b mtseek operation). .hp \fbgmt_bot\fp(\fix\fp): the tape is positioned at the beginning of the first file (always false after an .b mtseek operation). .hp \fbgmt_eot\fp(\fix\fp): a tape operation has reached the physical end of tape. .hp \fbgmt_sm\fp(\fix\fp): the tape is currently positioned at a setmark (always false after an .b mtseek operation). .hp \fbgmt_eod\fp(\fix\fp): the tape is positioned at the end of recorded data. .hp \fbgmt_wr_prot\fp(\fix\fp): the drive is write-protected. for some drives this can also mean that the drive does not support writing on the current medium type. .hp \fbgmt_online\fp(\fix\fp): the last .br open (2) found the drive with a tape in place and ready for operation. .hp \fbgmt_d_6250\fp(\fix\fp), \fbgmt_d_1600\fp(\fix\fp), \fbgmt_d_800\fp(\fix\fp): this \(lqgeneric\(rq status information reports the current density setting for 9-track \(12" tape drives only. .hp \fbgmt_dr_open\fp(\fix\fp): the drive does not have a tape in place. .hp \fbgmt_im_rep_en\fp(\fix\fp): immediate report mode. this bit is set if there are no guarantees that the data has been physically written to the tape when the write call returns. it is set zero only when the driver does not buffer data and the drive is set not to buffer data. .hp \fbgmt_cln\fp(\fix\fp): the drive has requested cleaning. implemented in kernels since 2.4.19 and 2.5.43. .re .tp \fimt_erreg\fp the only field defined in .i mt_erreg is the recovered error count in the low 16 bits (as defined by .br mt_st_softerr_shift and .br mt_st_softerr_mask ). due to inconsistencies in the way drives report recovered errors, this count is often not maintained (most drives do not by default report soft errors but this can be changed with a scsi mode select command). .tp \fimt_fileno\fp reports the current file number (zero-based). this value is set to \-1 when the file number is unknown (e.g., after .br mtbss or .br mtseek ). .tp \fimt_blkno\fp reports the block number (zero-based) within the current file. this value is set to \-1 when the block number is unknown (e.g., after .br mtbsf , .br mtbss , or .br mtseek ). .ss mtiocpos \(em get tape position this request takes an argument of type .i "(struct mtpos\ *)" and reports the drive's notion of the current tape block number, which is not the same as .i mt_blkno returned by .br mtiocget . this drive must be a scsi-2 drive that supports the .b "read position" command (device-specific address) or a tandberg-compatible scsi-1 drive (tandberg, archive viper, wangtek, ... ). .pp .in +4n .ex /* structure for mtiocpos \- mag tape get position command */ struct mtpos { long mt_blkno; /* current block number */ }; .ee .in .sh return value .tp .b eacces an attempt was made to write or erase a write-protected tape. (this error is not detected during .br open (2).) .tp .b ebusy the device is already in use or the driver was unable to allocate a buffer. .tp .b efault the command parameters point to memory not belonging to the calling process. .tp .b einval an .br ioctl (2) had an invalid argument, or a requested block size was invalid. .tp .b eio the requested operation could not be completed. .tp .b enomem the byte count in .br read (2) is smaller than the next physical block on the tape. (before 2.2.18 and 2.4.0 the extra bytes have been .\" precisely: linux 2.6.0-test6 silently ignored.) .tp .b enospc a write operation could not be completed because the tape reached end-of-medium. .tp .b enosys unknown .br ioctl (2). .tp .b enxio during opening, the tape device does not exist. .tp .b eoverflow an attempt was made to read or write a variable-length block that is larger than the driver's internal buffer. .tp .b erofs open is attempted with .b o_wronly or .b o_rdwr when the tape in the drive is write-protected. .sh files .tp .i /dev/st* the auto-rewind scsi tape devices .tp .i /dev/nst* the nonrewind scsi tape devices .\" .sh author .\" the driver has been written by kai m\(:akisara (kai.makisara@metla.fi) .\" starting from a driver written by dwayne forsyth. .\" several other .\" people have also contributed to the driver. .sh notes .ip 1. 4 when exchanging data between systems, both systems have to agree on the physical tape block size. the parameters of a drive after startup are often not the ones most operating systems use with these devices. most systems use drives in variable-block mode if the drive supports that mode. this applies to most modern drives, including dats, 8mm helical scan drives, dlts, etc. it may be advisable to use these drives in variable-block mode also in linux (i.e., use .b mtsetblk or .b mtsetdefblk at system startup to set the mode), at least when exchanging data with a foreign system. the drawback of this is that a fairly large tape block size has to be used to get acceptable data transfer rates on the scsi bus. .ip 2. many programs (e.g., .br tar (1)) allow the user to specify the blocking factor on the command line. note that this determines the physical block size on tape only in variable-block mode. .ip 3. in order to use scsi tape drives, the basic scsi driver, a scsi-adapter driver and the scsi tape driver must be either configured into the kernel or loaded as modules. if the scsi-tape driver is not present, the drive is recognized but the tape support described in this page is not available. .ip 4. the driver writes error messages to the console/log. the sense codes written into some messages are automatically translated to text if verbose scsi messages are enabled in kernel configuration. .ip 5. the driver's internal buffering allows good throughput in fixed-block mode also with small .br read (2) and .br write (2) byte counts. with direct transfers this is not possible and may cause a surprise when moving to the 2.6 kernel. the solution is to tell the software to use larger transfers (often telling it to use larger blocks). if this is not possible, direct transfers can be disabled. .sh see also .br mt (1) .pp the file .i drivers/scsi/readme.st or .i documentation/scsi/st.txt (kernel >= 2.6) in the linux kernel source tree contains the most recent information about the driver and its configuration possibilities .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getspnam.3 .\" copyright (c) bruno haible .\" .\" %%%license_start(gplv2+_doc_onepara) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" %%%license_end .\" .\" references consulted: .\" gnu glibc-2 source code and manual .\" dinkumware c library reference http://www.dinkumware.com/ .\" opengroup's single unix specification http://www.unix-systems.org/online.html .\" iso/iec 9899:1999 .\" .th wcspbrk 3 2021-03-22 "gnu" "linux programmer's manual" .sh name wcspbrk \- search a wide-character string for any of a set of wide characters .sh synopsis .nf .b #include .pp .bi "wchar_t *wcspbrk(const wchar_t *" wcs ", const wchar_t *" accept ); .fi .sh description the .br wcspbrk () function is the wide-character equivalent of the .br strpbrk (3) function. it searches for the first occurrence in the wide-character string pointed to by .i wcs of any of the characters in the wide-character string pointed to by .ir accept . .sh return value the .br wcspbrk () function returns a pointer to the first occurrence in .i wcs of any of the characters listed in .ir accept . if .i wcs contains none of these characters, null is returned. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br wcspbrk () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c99. .sh see also .br strpbrk (3), .br wcschr (3), .br wcscspn (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/utf-8.7 .\" copyright (c) 1993 by thomas koenig (ig25@rz.uni-karlsruhe.de) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified sat jul 24 18:42:59 1993 by rik faith (faith@cs.unc.edu) .th puts 3 2021-03-22 "gnu" "linux programmer's manual" .sh name fputc, fputs, putc, putchar, puts \- output of characters and strings .sh synopsis .nf .b #include .pp .bi "int fputc(int " c ", file *" stream ); .bi "int putc(int " c ", file *" stream ); .bi "int putchar(int " c ); .pp .bi "int fputs(const char *restrict " s ", file *restrict " stream ); .bi "int puts(const char *" s ); .fi .sh description .br fputc () writes the character .ir c , cast to an .ir "unsigned char" , to .ir stream . .pp .br putc () is equivalent to .br fputc () except that it may be implemented as a macro which evaluates .i stream more than once. .pp .bi "putchar(" c ) is equivalent to .bi "putc(" c ", " stdout ) \fr. .pp .br fputs () writes the string .i s to .ir stream , without its terminating null byte (\(aq\e0\(aq). .pp .br puts () writes the string .i s and a trailing newline to .ir stdout . .pp calls to the functions described here can be mixed with each other and with calls to other output functions from the .i stdio library for the same output stream. .pp for nonlocking counterparts, see .br unlocked_stdio (3). .sh return value .br fputc (), .br putc (), and .br putchar () return the character written as an .i unsigned char cast to an .i int or .b eof on error. .pp .br puts () and .br fputs () return a nonnegative number on success, or .b eof on error. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br fputc (), .br fputs (), .br putc (), .br putchar (), .br puts () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, c89, c99. .sh bugs it is not advisable to mix calls to output functions from the .i stdio library with low-level calls to .br write (2) for the file descriptor associated with the same output stream; the results will be undefined and very probably not what you want. .sh see also .br write (2), .br ferror (3), .br fgets (3), .br fopen (3), .br fputwc (3), .br fputws (3), .br fseek (3), .br fwrite (3), .br putwchar (3), .br scanf (3), .br unlocked_stdio (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-6.7 .so man3/slist.3 .\" copyright (c) 2014 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th uselocale 3 2021-03-22 "linux" "linux programmer's manual" .sh name uselocale \- set/get the locale for the calling thread .sh synopsis .nf .b #include .pp .bi "locale_t uselocale(locale_t " newloc ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br uselocale (): .nf since glibc 2.10: _xopen_source >= 700 before glibc 2.10: _gnu_source .fi .sh description the .br uselocale () function sets the current locale for the calling thread, and returns the thread's previously current locale. after a successful call to .br uselocale (), any calls by this thread to functions that depend on the locale will operate as though the locale has been set to .ir newloc . .pp the .i newloc argument can have one of the following values: .tp a handle returned by a call to \fbnewlocale\fp(3) or \fbduplocale\fp(3) the calling thread's current locale is set to the specified locale. .tp the special locale object handle \fblc_global_locale\fp the calling thread's current locale is set to the global locale determined by .br setlocale (3). .tp .i "(locale_t) 0" the calling thread's current locale is left unchanged (and the current locale is returned as the function result). .sh return value on success, .br uselocale () returns the locale handle that was set by the previous call to .br uselocale () in this thread, or .b lc_global_locale if there was no such previous call. on error, it returns .ir "(locale_t)\ 0" , and sets .i errno to indicate the error. .sh errors .tp .b einval .i newloc does not refer to a valid locale object. .sh versions the .br uselocale () function first appeared in version 2.3 of the gnu c library. .sh conforming to posix.1-2008. .sh notes unlike .br setlocale (3), .br uselocale () does not allow selective replacement of individual locale categories. to employ a locale that differs in only a few categories from the current locale, use calls to .br duplocale (3) and .br newlocale (3) to obtain a locale object equivalent to the current locale and modify the desired categories in that object. .sh examples see .br newlocale (3) and .br duplocale (3). .sh see also .br locale (1), .br duplocale (3), .br freelocale (3), .br newlocale (3), .br setlocale (3), .br locale (5), .br locale (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 1980, 1991 regents of the university of california. .\" all rights reserved. .\" .\" this code is derived from software contributed to berkeley by .\" the american national standards committee x3, on information .\" processing systems. .\" .\" %%%license_start(bsd_4_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. all advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" this product includes software developed by the university of .\" california, berkeley and its contributors. .\" 4. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" @(#)setbuf.3 6.10 (berkeley) 6/29/91 .\" .\" converted for linux, mon nov 29 14:55:24 1993, faith@cs.unc.edu .\" added section to bugs, sun mar 12 22:28:33 met 1995, .\" thomas.koenig@ciw.uni-karlsruhe.de .\" correction, sun, 11 apr 1999 15:55:18, .\" martin vicente .\" correction, 2000-03-03, andreas jaeger .\" added return value for setvbuf, aeb, .\" .th setbuf 3 2021-03-22 "linux" "linux programmer's manual" .sh name setbuf, setbuffer, setlinebuf, setvbuf \- stream buffering operations .sh synopsis .nf .b #include .pp .bi "int setvbuf(file *restrict " stream ", char *restrict " buf , .bi " int " mode ", size_t " size ); .pp .bi "void setbuf(file *restrict " stream ", char *restrict " buf ); .bi "void setbuffer(file *restrict " stream ", char *restrict " buf , .bi " size_t " size ); .bi "void setlinebuf(file *" stream ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br setbuffer (), .br setlinebuf (): .nf since glibc 2.19: _default_source glibc 2.19 and earlier: _bsd_source .fi .sh description the three types of buffering available are unbuffered, block buffered, and line buffered. when an output stream is unbuffered, information appears on the destination file or terminal as soon as written; when it is block buffered, many characters are saved up and written as a block; when it is line buffered, characters are saved up until a newline is output or input is read from any stream attached to a terminal device (typically \fistdin\fp). the function .br fflush (3) may be used to force the block out early. (see .br fclose (3).) .pp normally all files are block buffered. if a stream refers to a terminal (as .i stdout normally does), it is line buffered. the standard error stream .i stderr is always unbuffered by default. .pp the .br setvbuf () function may be used on any open stream to change its buffer. the .i mode argument must be one of the following three macros: .rs .tp .b _ionbf unbuffered .tp .b _iolbf line buffered .tp .b _iofbf fully buffered .re .pp except for unbuffered files, the .i buf argument should point to a buffer at least .i size bytes long; this buffer will be used instead of the current buffer. if the argument .i buf is null, only the mode is affected; a new buffer will be allocated on the next read or write operation. the .br setvbuf () function may be used only after opening a stream and before any other operations have been performed on it. .pp the other three calls are, in effect, simply aliases for calls to .br setvbuf (). the .br setbuf () function is exactly equivalent to the call .pp .in +4n setvbuf(stream, buf, buf ? _iofbf : _ionbf, bufsiz); .in .pp the .br setbuffer () function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default .br bufsiz . the .br setlinebuf () function is exactly equivalent to the call: .pp .in +4n setvbuf(stream, null, _iolbf, 0); .in .sh return value the function .br setvbuf () returns 0 on success. it returns nonzero on failure .ri ( mode is invalid or the request cannot be honored). it may set .i errno on failure. .pp the other functions do not return a value. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br setbuf (), .br setbuffer (), .br setlinebuf (), .br setvbuf () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to the .br setbuf () and .br setvbuf () functions conform to c89 and c99. .sh notes posix notes .\" https://www.austingroupbugs.net/view.php?id=397#c799 .\" 0000397: setbuf and errno that the value of .i errno is unspecified after a call to .br setbuf () and further notes that, since the value of .i errno is not required to be unchanged after a successful call to .br setbuf (), applications should instead use .br setvbuf () in order to detect errors. .sh bugs .\" the .\" .br setbuffer () .\" and .\" .br setlinebuf () .\" functions are not portable to versions of bsd before 4.2bsd, and .\" are available under linux since libc 4.5.21. .\" on 4.2bsd and 4.3bsd systems, .\" .br setbuf () .\" always uses a suboptimal buffer size and should be avoided. .\".pp you must make sure that the space that .i buf points to still exists by the time .i stream is closed, which also happens at program termination. for example, the following is invalid: .pp .ex #include int main(void) { char buf[bufsiz]; setbuf(stdout, buf); printf("hello, world!\en"); return 0; } .ee .sh see also .br stdbuf (1), .br fclose (3), .br fflush (3), .br fopen (3), .br fread (3), .br malloc (3), .br printf (3), .br puts (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-4.7 .so man7/system_data_types.7 .\" this manpage is copyright (c) 1992 drew eckhardt; .\" and copyright (c) 1993 michael haardt, ian jackson. .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified wed jul 21 19:42:57 1993 by rik faith .\" modified sun jul 21 21:25:26 1996 by andries brouwer .\" modified wed nov 6 03:46:05 1996 by eric s. raymond .\" .th alarm 2 2017-05-03 "linux" "linux programmer's manual" .sh name alarm \- set an alarm clock for delivery of a signal .sh synopsis .nf .b #include .pp .bi "unsigned int alarm(unsigned int " seconds ); .fi .sh description .br alarm () arranges for a .b sigalrm signal to be delivered to the calling process in .i seconds seconds. .pp if .i seconds is zero, any pending alarm is canceled. .pp in any event any previously set .br alarm () is canceled. .sh return value .br alarm () returns the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm. .sh conforming to posix.1-2001, posix.1-2008, svr4, 4.3bsd. .sh notes .br alarm () and .br setitimer (2) share the same timer; calls to one will interfere with use of the other. .pp alarms created by .br alarm () are preserved across .br execve (2) and are not inherited by children created via .br fork (2). .pp .br sleep (3) may be implemented using .br sigalrm ; mixing calls to .br alarm () and .br sleep (3) is a bad idea. .pp scheduling delays can, as ever, cause the execution of the process to be delayed by an arbitrary amount of time. .sh see also .br gettimeofday (2), .br pause (2), .br select (2), .br setitimer (2), .br sigaction (2), .br signal (2), .br timer_create (2), .br timerfd_create (2), .br sleep (3), .br time (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/system_data_types.7 .so man3/erf.3 .\" %%%license_start(public_domain) .\" this page is in the public domain. - aeb .\" %%%license_end .\" .\" 2004-12-17, mtk, added description of ptsname_r() + errors .\" .th ptsname 3 2021-03-22 "" "linux programmer's manual" .sh name ptsname, ptsname_r \- get the name of the slave pseudoterminal .sh synopsis .nf .b #include .pp .bi "char *ptsname(int " fd ");" .bi "int ptsname_r(int " fd ", char *" buf ", size_t " buflen ");" .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br ptsname (): .nf since glibc 2.24: _xopen_source >= 500 .\" || (_xopen_source && _xopen_source_extended) glibc 2.23 and earlier: _xopen_source .fi .pp .br ptsname_r (): .nf _gnu_source .fi .sh description the .br ptsname () function returns the name of the slave pseudoterminal device corresponding to the master referred to by the file descriptor .ir fd . .pp the .br ptsname_r () function is the reentrant equivalent of .br ptsname (). it returns the name of the slave pseudoterminal device as a null-terminated string in the buffer pointed to by .ir buf . the .i buflen argument specifies the number of bytes available in .ir buf . .sh return value on success, .br ptsname () returns a pointer to a string in static storage which will be overwritten by subsequent calls. this pointer must not be freed. on failure, null is returned. .pp on success, .br ptsname_r () returns 0. on failure, an error number is returned to indicate the error. .\" in glibc, the error number is not only returned as the return value .\" but also stored in errno. but this is not true for musl libc. .sh errors .tp .b einval .rb ( ptsname_r () only) .i buf is null. (this error is returned only for .\" glibc commit 8f0a947cf55f3b0c4ebdf06953c57eff67a22fa9 glibc 2.25 and earlier.) .tp .b enotty .i fd does not refer to a pseudoterminal master device. .tp .b erange .rb ( ptsname_r () only) .i buf is too small. .sh versions .br ptsname () is provided in glibc since version 2.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br ptsname () t} thread safety mt-unsafe race:ptsname t{ .br ptsname_r () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to .br ptsname (): posix.1-2001, posix.1-2008. .pp .br ptsname () is part of the unix 98 pseudoterminal support (see .br pts (4)). .pp .br ptsname_r () is a linux extension, that is proposed for inclusion .\" fixme . for later review when issue 8 is one day released .\" http://austingroupbugs.net/tag_view_page.php?tag_id=8 .\" http://austingroupbugs.net/view.php?id=508 in the next major revision of posix.1 (issue 8). a version of this function is documented on tru64 and hp-ux, but on those implementations, \-1 is returned on error, with .i errno set to indicate the error. avoid using this function in portable programs. .sh see also .br grantpt (3), .br posix_openpt (3), .br ttyname (3), .br unlockpt (3), .br pts (4), .br pty (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/setresuid.2 .so man3/getutent.3 .so man7/system_data_types.7 .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" and copyright 2008, linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified 1993-07-24 by rik faith (faith@cs.unc.edu) .\" modified 2002-07-25 by walter harms .\" (walter.harms@informatik.uni-oldenburg.de) .\" .th asin 3 2021-03-22 "" "linux programmer's manual" .sh name asin, asinf, asinl \- arc sine function .sh synopsis .nf .b #include .pp .bi "double asin(double " x ); .bi "float asinf(float " x ); .bi "long double asinl(long double " x ); .fi .pp link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br asinf (), .br asinl (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description these functions calculate the principal value of the arc sine of .ir x ; that is the value whose sine is .ir x . .sh return value on success, these functions return the principal value of the arc sine of .ir x in radians; the return value is in the range [\-pi/2,\ pi/2]. .pp if .i x is a nan, a nan is returned. .pp if .i x is +0 (\-0), +0 (\-0) is returned. .pp if .i x is outside the range [\-1,\ 1], a domain error occurs, and a nan is returned. .\" .\" posix.1-2001 documents an optional range error for subnormal x; .\" glibc 2.8 does not do this. .sh errors see .br math_error (7) for information on how to determine whether an error has occurred when calling these functions. .pp the following errors can occur: .tp domain error: \fix\fp is outside the range [\-1,\ 1] .i errno is set to .br edom . an invalid floating-point exception .rb ( fe_invalid ) is raised. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br asin (), .br asinf (), .br asinl () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to c99, posix.1-2001, posix.1-2008. .pp the variant returning .i double also conforms to svr4, 4.3bsd, c89. .sh see also .br acos (3), .br atan (3), .br atan2 (3), .br casin (3), .br cos (3), .br sin (3), .br tan (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/getpwent.3 .so man3/log10.3 .so man3/fseek.3 .so man7/iso_8859-4.7 .\" $netbsd: rcmd.3,v 1.9 1996/05/28 02:07:39 mrg exp $ .\" .\" copyright (c) 1983, 1991, 1993 .\" the regents of the university of california. all rights reserved. .\" .\" %%%license_start(bsd_4_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. all advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" this product includes software developed by the university of .\" california, berkeley and its contributors. .\" 4. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" @(#)rcmd.3 8.1 (berkeley) 6/4/93 .\" .\" contributed as linux man page by david a. holland, 970908 .\" i have not checked whether the linux situation is exactly the same. .\" .\" 2007-12-08, mtk, converted from mdoc to man macros .\" .th rcmd 3 2021-03-22 "linux" "linux programmer's manual" .sh name rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_af, ruserok_af \- routines for returning a stream to a remote command .sh synopsis .nf .br "#include " "/* or on some systems */" .pp .bi "int rcmd(char **restrict " ahost ", unsigned short " inport , .bi " const char *restrict " locuser , .bi " const char *restrict " remuser , .bi " const char *restrict " cmd ", int *restrict " fd2p ); .pp .bi "int rresvport(int *" port ); .pp .bi "int iruserok(uint32_t " raddr ", int " superuser , .bi " const char *" ruser ", const char *" luser ); .bi "int ruserok(const char *" rhost ", int " superuser , .bi " const char *" ruser ", const char *" luser ); .pp .bi "int rcmd_af(char **restrict " ahost ", unsigned short " inport , .bi " const char *restrict " locuser , .bi " const char *restrict " remuser , .bi " const char *restrict " cmd ", int *restrict " fd2p , .bi " sa_family_t " af ); .pp .bi "int rresvport_af(int *" port ", sa_family_t " af ); .pp .bi "int iruserok_af(const void *restrict " raddr ", int " superuser , .bi " const char *restrict " ruser ", const char *restrict " luser , .bi " sa_family_t " af ); .bi "int ruserok_af(const char *" rhost ", int " superuser , .bi " const char *" ruser ", const char *" luser , .bi " sa_family_t " af ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .ad l .pp .br rcmd (), .br rcmd_af (), .br rresvport (), .br rresvport_af (), .br iruserok (), .br iruserok_af (), .br ruserok (), .br ruserok_af (): .nf since glibc 2.19: _default_source glibc 2.19 and earlier: _bsd_source .fi .ad .sh description the .br rcmd () function is used by the superuser to execute a command on a remote machine using an authentication scheme based on privileged port numbers. the .br rresvport () function returns a file descriptor to a socket with an address in the privileged port space. the .br iruserok () and .br ruserok () functions are used by servers to authenticate clients requesting service with .br rcmd (). all four functions are used by the .br rshd (8) server (among others). .ss rcmd() the .br rcmd () function looks up the host .i *ahost using .br gethostbyname (3), returning \-1 if the host does not exist. otherwise, .i *ahost is set to the standard name of the host and a connection is established to a server residing at the well-known internet port .ir inport . .pp if the connection succeeds, a socket in the internet domain of type .br sock_stream is returned to the caller, and given to the remote command as .ir stdin and .ir stdout . if .i fd2p is nonzero, then an auxiliary channel to a control process will be set up, and a file descriptor for it will be placed in .ir *fd2p . the control process will return diagnostic output from the command (unit 2) on this channel, and will also accept bytes on this channel as being unix signal numbers, to be forwarded to the process group of the command. if .i fd2p is 0, then the .ir stderr (unit 2 of the remote command) will be made the same as the .ir stdout and no provision is made for sending arbitrary signals to the remote process, although you may be able to get its attention by using out-of-band data. .pp the protocol is described in detail in .br rshd (8). .ss rresvport() the .br rresvport () function is used to obtain a socket with a privileged port bound to it. this socket is suitable for use by .br rcmd () and several other functions. privileged ports are those in the range 0 to 1023. only a privileged process (on linux, a process that has the .b cap_net_bind_service capability in the user namespace governing its network namespace) is allowed to bind to a privileged port. in the glibc implementation, this function restricts its search to the ports from 512 to 1023. the .i port argument is value-result: the value it supplies to the call is used as the starting point for a circular search of the port range; on (successful) return, it contains the port number that was bound to. .\" .ss iruserok() and ruserok() the .br iruserok () and .br ruserok () functions take a remote host's ip address or name, respectively, two usernames and a flag indicating whether the local user's name is that of the superuser. then, if the user is .i not the superuser, it checks the .ir /etc/hosts.equiv file. if that lookup is not done, or is unsuccessful, the .ir .rhosts in the local user's home directory is checked to see if the request for service is allowed. .pp if this file does not exist, is not a regular file, is owned by anyone other than the user or the superuser, is writable by anyone other than the owner, or is hardlinked anywhere, the check automatically fails. zero is returned if the machine name is listed in the .ir hosts.equiv file, or the host and remote username are found in the .ir .rhosts file; otherwise .br iruserok () and .br ruserok () return \-1. if the local domain (as obtained from .br gethostname (2)) is the same as the remote domain, only the machine name need be specified. .pp if the ip address of the remote host is known, .br iruserok () should be used in preference to .br ruserok (), as it does not require trusting the dns server for the remote host's domain. .ss *_af() variants all of the functions described above work with ipv4 .rb ( af_inet ) sockets. the "_af" variants take an extra argument that allows the socket address family to be specified. for these functions, the .i af argument can be specified as .br af_inet or .br af_inet6 . in addition, .br rcmd_af () supports the use of .br af_unspec . .sh return value the .br rcmd () function returns a valid socket descriptor on success. it returns \-1 on error and prints a diagnostic message on the standard error. .pp the .br rresvport () function returns a valid, bound socket descriptor on success. on failure, it returns \-1 and sets .i errno to indicate the error. the error code .br eagain is overloaded to mean: "all network ports in use". .pp for information on the return from .br ruserok () and .br iruserok (), see above. .sh versions the functions .br iruserok_af (), .br rcmd_af (), .br rresvport_af (), and .br ruserok_af () functions are provide in glibc since version 2.2. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br rcmd (), .br rcmd_af () t} thread safety mt-unsafe t{ .br rresvport (), .br rresvport_af () t} thread safety mt-safe t{ .br iruserok (), .br ruserok (), .br iruserok_af (), .br ruserok_af () t} thread safety mt-safe locale .te .hy .ad .sp 1 .sh conforming to not in posix.1. present on the bsds, solaris, and many other systems. these functions appeared in 4.2bsd. the "_af" variants are more recent additions, and are not present on as wide a range of systems. .sh bugs .br iruserok () and .br iruserok_af () are declared in glibc headers only since version 2.12. .\" bug filed 25 nov 2007: .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=5399 .sh see also .br rlogin (1), .br rsh (1), .br rexec (3), .br rexecd (8), .br rlogind (8), .br rshd (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2003 free software foundation, inc. .\" .\" %%%license_start(gpl_noversion_oneline) .\" this file is distributed according to the gnu general public license. .\" %%%license_end .\" .th io_setup 2 2021-03-22 "linux" "linux programmer's manual" .sh name io_setup \- create an asynchronous i/o context .sh synopsis .nf .br "#include " " /* defines needed types */" .pp .bi "long io_setup(unsigned int " nr_events ", aio_context_t *" ctx_idp ); .fi .pp .ir note : there is no glibc wrapper for this system call; see notes. .sh description .ir note : this page describes the raw linux system call interface. the wrapper function provided by .i libaio uses a different type for the .i ctx_idp argument. see notes. .pp the .br io_setup () system call creates an asynchronous i/o context suitable for concurrently processing \finr_events\fp operations. the .i ctx_idp argument must not point to an aio context that already exists, and must be initialized to 0 prior to the call. on successful creation of the aio context, \fi*ctx_idp\fp is filled in with the resulting handle. .sh return value on success, .br io_setup () returns 0. for the failure return, see notes. .sh errors .tp .b eagain the specified \finr_events\fp exceeds the limit of available events, as defined in .ir /proc/sys/fs/aio\-max\-nr (see .br proc (5)). .tp .b efault an invalid pointer is passed for \fictx_idp\fp. .tp .b einval \fictx_idp\fp is not initialized, or the specified \finr_events\fp exceeds internal limits. \finr_events\fp should be greater than 0. .tp .b enomem insufficient kernel resources are available. .tp .b enosys .br io_setup () is not implemented on this architecture. .sh versions the asynchronous i/o system calls first appeared in linux 2.5. .sh conforming to .br io_setup () is linux-specific and should not be used in programs that are intended to be portable. .sh notes glibc does not provide a wrapper for this system call. you could invoke it using .br syscall (2). but instead, you probably want to use the .br io_setup () wrapper function provided by .\" http://git.fedorahosted.org/git/?p=libaio.git .ir libaio . .pp note that the .i libaio wrapper function uses a different type .ri ( "io_context_t\ *" ) .\" but glibc is confused, since uses 'io_context_t' to declare .\" the system call. for the .i ctx_idp argument. note also that the .i libaio wrapper does not follow the usual c library conventions for indicating errors: on error it returns a negated error number (the negative of one of the values listed in errors). if the system call is invoked via .br syscall (2), then the return value follows the usual conventions for indicating an error: \-1, with .i errno set to a (positive) value that indicates the error. .sh see also .br io_cancel (2), .br io_destroy (2), .br io_getevents (2), .br io_submit (2), .br aio (7) .\" .sh author .\" kent yoder. .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/xdr.3 .so man3/stailq.3 .so man3/regex.3 .\" copyright (c) 2006 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th mq_unlink 3 2021-03-22 "linux" "linux programmer's manual" .sh name mq_unlink \- remove a message queue .sh synopsis .nf .b #include .pp .bi "int mq_unlink(const char *" name ); .fi .pp link with \fi\-lrt\fp. .sh description .br mq_unlink () removes the specified message queue .ir name . the message queue name is removed immediately. the queue itself is destroyed once any other processes that have the queue open close their descriptors referring to the queue. .sh return value on success .br mq_unlink () returns 0; on error, \-1 is returned, with .i errno set to indicate the error. .sh errors .tp .b eacces the caller does not have permission to unlink this message queue. .tp .b enametoolong .i name was too long. .tp .b enoent there is no message queue with the given .ir name . .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br mq_unlink () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh see also .br mq_close (3), .br mq_getattr (3), .br mq_notify (3), .br mq_open (3), .br mq_receive (3), .br mq_send (3), .br mq_overview (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/sigsetops.3 .\" copyright (c) 1993 .\" the regents of the university of california. all rights reserved. .\" and copyright (c) 2020 by alejandro colomar .\" .\" %%%license_start(bsd_3_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" .th slist 3 2021-03-22 "gnu" "linux programmer's manual" .sh name slist_empty, slist_entry, slist_first, slist_foreach, .\"slist_foreach_from, .\"slist_foreach_from_safe, .\"slist_foreach_safe, slist_head, slist_head_initializer, slist_init, slist_insert_after, slist_insert_head, slist_next, slist_remove, .\"slist_remove_after, slist_remove_head .\"slist_swap \- implementation of a singly linked list .sh synopsis .nf .b #include .pp .b slist_entry(type); .pp .b slist_head(headname, type); .bi "slist_head slist_head_initializer(slist_head " head ); .bi "void slist_init(slist_head *" head ); .pp .bi "int slist_empty(slist_head *" head ); .pp .bi "void slist_insert_head(slist_head *" head , .bi " struct type *" elm ", slist_entry " name ); .bi "void slist_insert_after(struct type *" listelm , .bi " struct type *" elm ", slist_entry " name ); .pp .bi "struct type *slist_first(slist_head *" head ); .bi "struct type *slist_next(struct type *" elm ", slist_entry " name ); .pp .bi "slist_foreach(struct type *" var ", slist_head *" head ", slist_entry " name ); .\" .bi "slist_foreach_from(struct type *" var ", slist_head *" head , .\" .bi " slist_entry " name ); .\" .pp .\" .bi "slist_foreach_safe(struct type *" var ", slist_head *" head , .\" .bi " slist_entry " name ", struct type *" temp_var ); .\" .bi "slist_foreach_from_safe(struct type *" var ", slist_head *" head , .\" .bi " slist_entry " name ", struct type *" temp_var ); .pp .bi "void slist_remove(slist_head *" head ", struct type *" elm , .bi " slist_entry " name ); .bi "void slist_remove_head(slist_head *" head , .bi " slist_entry " name ); .\" .bi "void slist_remove_after(struct type *" elm , .\" .bi " slist_entry " name ); .\" .pp .\" .bi "void slist_swap(slist_head *" head1 ", slist_head *" head2 , .\" .bi " slist_entry " name ); .fi .sh description these macros define and operate on doubly linked lists. .pp in the macro definitions, .i type is the name of a user-defined structure, that must contain a field of type .ir slist_entry , named .ir name . the argument .ir headname is the name of a user-defined structure that must be declared using the macro .br slist_head (). .ss creation a singly linked list is headed by a structure defined by the .br slist_head () macro. this structure contains a single pointer to the first element on the list. the elements are singly linked for minimum space and pointer manipulation overhead at the expense of o(n) removal for arbitrary elements. new elements can be added to the list after an existing element or at the head of the list. an .i slist_head structure is declared as follows: .pp .in +4 .ex slist_head(headname, type) head; .ee .in .pp where .i struct headname is the structure to be defined, and .i struct type is the type of the elements to be linked into the list. a pointer to the head of the list can later be declared as: .pp .in +4 .ex struct headname *headp; .ee .in .pp (the names .i head and .i headp are user selectable.) .pp .br slist_entry () declares a structure that connects the elements in the list. .pp .br slist_head_initializer () evaluates to an initializer for the list .ir head . .pp .br slist_init () initializes the list referenced by .ir head . .pp .br slist_empty () evaluates to true if there are no elements in the list. .ss insertion .br slist_insert_head () inserts the new element .i elm at the head of the list. .pp .br slist_insert_after () inserts the new element .i elm after the element .ir listelm . .ss traversal .br slist_first () returns the first element in the list, or null if the list is empty. .pp .br slist_next () returns the next element in the list. .pp .br slist_foreach () traverses the list referenced by .i head in the forward direction, assigning each element in turn to .ir var . .\" .pp .\" .br slist_foreach_from () .\" behaves identically to .\" .br slist_foreach () .\" when .\" .i var .\" is null, else it treats .\" .i var .\" as a previously found slist element and begins the loop at .\" .i var .\" instead of the first element in the slist referenced by .\" .ir head . .\" .pp .\" .br slist_foreach_safe () .\" traverses the list referenced by .\" .i head .\" in the forward direction, assigning each element in .\" turn to .\" .ir var . .\" however, unlike .\" .br slist_foreach () .\" here it is permitted to both remove .\" .i var .\" as well as free it from within the loop safely without interfering with the .\" traversal. .\" .pp .\" .br slist_foreach_from_safe () .\" behaves identically to .\" .br slist_foreach_safe () .\" when .\" .i var .\" is null, else it treats .\" .i var .\" as a previously found slist element and begins the loop at .\" .i var .\" instead of the first element in the slist referenced by .\" .ir head . .ss removal .br slist_remove () removes the element .i elm from the list. .pp .br slist_remove_head () removes the element .i elm from the head of the list. for optimum efficiency, elements being removed from the head of the list should explicitly use this macro instead of the generic .br slist_remove (). .\" .pp .\" .br slist_remove_after () .\" removes the element after .\" .i elm .\" from the list. .\" unlike .\" .ir slist_remove , .\" this macro does not traverse the entire list. .\" .ss other features .\" .br slist_swap () .\" swaps the contents of .\" .i head1 .\" and .\" .ir head2 . .sh return value .br slist_empty () returns nonzero if the list is empty, and zero if the list contains at least one entry. .pp .br slist_first (), and .br slist_next () return a pointer to the first or next .i type structure, respectively. .pp .br slist_head_initializer () returns an initializer that can be assigned to the list .ir head . .sh conforming to not in posix.1, posix.1-2001, or posix.1-2008. present on the bsds (slist macros first appeared in 4.4bsd). .sh bugs .br slist_foreach () doesn't allow .i var to be removed or freed within the loop, as it would interfere with the traversal. .br slist_foreach_safe (), which is present on the bsds but is not present in glibc, fixes this limitation by allowing .i var to safely be removed from the list and freed from within the loop without interfering with the traversal. .sh examples .ex #include #include #include #include struct entry { int data; slist_entry(entry) entries; /* singly linked list */ }; slist_head(slisthead, entry); int main(void) { struct entry *n1, *n2, *n3, *np; struct slisthead head; /* singly linked list head */ slist_init(&head); /* initialize the queue */ n1 = malloc(sizeof(struct entry)); /* insert at the head */ slist_insert_head(&head, n1, entries); n2 = malloc(sizeof(struct entry)); /* insert after */ slist_insert_after(n1, n2, entries); slist_remove(&head, n2, entry, entries);/* deletion */ free(n2); n3 = slist_first(&head); slist_remove_head(&head, entries); /* deletion from the head */ free(n3); for (int i = 0; i < 5; i++) { n1 = malloc(sizeof(struct entry)); slist_insert_head(&head, n1, entries); n1\->data = i; } /* forward traversal */ slist_foreach(np, &head, entries) printf("%i\en", np\->data); while (!slist_empty(&head)) { /* list deletion */ n1 = slist_first(&head); slist_remove_head(&head, entries); free(n1); } slist_init(&head); exit(exit_success); } .ee .sh see also .br insque (3), .br queue (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-1.7 .so man3/clog2.3 .so man3/des_crypt.3 .\" copyright (c), 1994, graeme w. wilford (wilf). .\" and copyright (c) 2010, 2014, 2015, michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" fri jul 29th 12:56:44 bst 1994 wilf. .\" changes inspired by patch from richard kettlewell .\" , aeb 970616. .\" modified, 27 may 2004, michael kerrisk .\" added notes on capability requirements .th setuid 2 2021-03-22 "linux" "linux programmer's manual" .sh name setuid \- set user identity .sh synopsis .nf .b #include .pp .bi "int setuid(uid_t " uid ); .fi .sh description .br setuid () sets the effective user id of the calling process. if the calling process is privileged (more precisely: if the process has the .br cap_setuid capability in its user namespace), the real uid and saved set-user-id are also set. .pp under linux, .br setuid () is implemented like the posix version with the .b _posix_saved_ids feature. this allows a set-user-id (other than root) program to drop all of its user privileges, do some un-privileged work, and then reengage the original effective user id in a secure manner. .pp if the user is root or the program is set-user-id-root, special care must be taken: .br setuid () checks the effective user id of the caller and if it is the superuser, all process-related user id's are set to .ir uid . after this has occurred, it is impossible for the program to regain root privileges. .pp thus, a set-user-id-root program wishing to temporarily drop root privileges, assume the identity of an unprivileged user, and then regain root privileges afterward cannot use .br setuid (). you can accomplish this with .br seteuid (2). .sh return value on success, zero is returned. on error, \-1 is returned, and .i errno is set to indicate the error. .pp .ir note : there are cases where .br setuid () can fail even when the caller is uid 0; it is a grave security error to omit checking for a failure return from .br setuid (). .sh errors .tp .b eagain the call would change the caller's real uid (i.e., .i uid does not match the caller's real uid), but there was a temporary failure allocating the necessary kernel data structures. .tp .b eagain .i uid does not match the real user id of the caller and this call would bring the number of processes belonging to the real user id .i uid over the caller's .b rlimit_nproc resource limit. since linux 3.1, this error case no longer occurs (but robust applications should check for this error); see the description of .b eagain in .br execve (2). .tp .b einval the user id specified in .i uid is not valid in this user namespace. .tp .b eperm the user is not privileged (linux: does not have the .b cap_setuid capability in its user namespace) and .i uid does not match the real uid or saved set-user-id of the calling process. .sh conforming to posix.1-2001, posix.1-2008, svr4. not quite compatible with the 4.4bsd call, which sets all of the real, saved, and effective user ids. .\" svr4 documents an additional einval error condition. .sh notes linux has the concept of the filesystem user id, normally equal to the effective user id. the .br setuid () call also sets the filesystem user id of the calling process. see .br setfsuid (2). .pp if .i uid is different from the old effective uid, the process will be forbidden from leaving core dumps. .pp the original linux .br setuid () system call supported only 16-bit user ids. subsequently, linux 2.4 added .br setuid32 () supporting 32-bit ids. the glibc .br setuid () wrapper function transparently deals with the variation across kernel versions. .\" .ss c library/kernel differences at the kernel level, user ids and group ids are a per-thread attribute. however, posix requires that all threads in a process share the same credentials. the nptl threading implementation handles the posix requirements by providing wrapper functions for the various system calls that change process uids and gids. these wrapper functions (including the one for .br setuid ()) employ a signal-based technique to ensure that when one thread changes credentials, all of the other threads in the process also change their credentials. for details, see .br nptl (7). .sh see also .br getuid (2), .br seteuid (2), .br setfsuid (2), .br setreuid (2), .br capabilities (7), .br credentials (7), .br user_namespaces (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/getresgid.2 .so man3/circleq.3 .so man3/remquo.3 .\" copyright (c) 2009 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_getcpuclockid 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_getcpuclockid \- retrieve id of a thread's cpu time clock .sh synopsis .nf .b #include .b #include .pp .bi "int pthread_getcpuclockid(pthread_t " thread ", clockid_t *" clockid ); .pp compile and link with \fi\-pthread\fp. .fi .sh description the .br pthread_getcpuclockid () function obtains the id of the cpu-time clock of the thread whose id is given in .ir thread , and returns it in the location pointed to by .ir clockid . .\" the clockid is constructed as follows: .\" *clockid = clock_thread_cputime_id | (pd->tid << clock_idfield_size) .\" where clock_idfield_size is 3. .sh return value on success, this function returns 0; on error, it returns a nonzero error number. .sh errors .tp .b enoent .\" clock_thread_cputime_id not defined per-thread cpu time clocks are not supported by the system. .\" .\" looking at nptl/pthread_getcpuclockid.c an erange error would .\" be possible if kernel thread ids took more than 29 bits (which .\" they currently cannot). .tp .b esrch no thread with the id .i thread could be found. .sh versions this function is available in glibc since version 2.2. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_getcpuclockid () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes when .i thread refers to the calling thread, this function returns an identifier that refers to the same clock manipulated by .br clock_gettime (2) and .br clock_settime (2) when given the clock id .br clock_thread_cputime_id . .sh examples the program below creates a thread and then uses .br clock_gettime (2) to retrieve the total process cpu time, and the per-thread cpu time consumed by the two threads. the following shell session shows an example run: .pp .in +4n .ex $ \fb./a.out\fp main thread sleeping subthread starting infinite loop main thread consuming some cpu time... process total cpu time: 1.368 main thread cpu time: 0.376 subthread cpu time: 0.992 .ee .in .ss program source \& .ex /* link with "\-lrt" */ #include #include #include #include #include #include #include #include #define handle_error(msg) \e do { perror(msg); exit(exit_failure); } while (0) #define handle_error_en(en, msg) \e do { errno = en; perror(msg); exit(exit_failure); } while (0) static void * thread_start(void *arg) { printf("subthread starting infinite loop\en"); for (;;) continue; } static void pclock(char *msg, clockid_t cid) { struct timespec ts; printf("%s", msg); if (clock_gettime(cid, &ts) == \-1) handle_error("clock_gettime"); printf("%4jd.%03ld\en", (intmax_t) ts.tv_sec, ts.tv_nsec / 1000000); } int main(int argc, char *argv[]) { pthread_t thread; clockid_t cid; int s; s = pthread_create(&thread, null, thread_start, null); if (s != 0) handle_error_en(s, "pthread_create"); printf("main thread sleeping\en"); sleep(1); printf("main thread consuming some cpu time...\en"); for (int j = 0; j < 2000000; j++) getppid(); pclock("process total cpu time: ", clock_process_cputime_id); s = pthread_getcpuclockid(pthread_self(), &cid); if (s != 0) handle_error_en(s, "pthread_getcpuclockid"); pclock("main thread cpu time: ", cid); /* the preceding 4 lines of code could have been replaced by: pclock("main thread cpu time: ", clock_thread_cputime_id); */ s = pthread_getcpuclockid(thread, &cid); if (s != 0) handle_error_en(s, "pthread_getcpuclockid"); pclock("subthread cpu time: 1 ", cid); exit(exit_success); /* terminates both threads */ } .ee .sh see also .br clock_gettime (2), .br clock_settime (2), .br timer_create (2), .br clock_getcpuclockid (3), .br pthread_self (3), .br pthreads (7), .br time (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/unimplemented.2 .so man3/getservent.3 .so man3/slist.3 .so man3/gethostbyname.3 .\" copyright (c) 2006 michael kerrisk .\" .\" %%%license_start(permissive_misc) .\" permission is hereby granted, free of charge, to any person obtaining .\" a copy of this software and associated documentation files (the .\" "software"), to deal in the software without restriction, including .\" without limitation the rights to use, copy, modify, merge, publish, .\" distribute, sublicense, and/or sell copies of the software, and to .\" permit persons to whom the software is furnished to do so, subject to .\" the following conditions: .\" .\" the above copyright notice and this permission notice shall be .\" included in all copies or substantial portions of the software. .\" .\" the software is provided "as is", without warranty of any kind, .\" express or implied, including but not limited to the warranties of .\" merchantability, fitness for a particular purpose and noninfringement. .\" in no event shall the authors or copyright holders be liable for any .\" claim, damages or other liability, whether in an action of contract, .\" tort or otherwise, arising from, out of or in connection with the .\" software or the use or other dealings in the software. .\" %%%license_end .\" .th invocation_name 3 2017-09-15 "gnu" "linux programmer's manual" .sh name program_invocation_name, program_invocation_short_name \- \ obtain name used to invoke calling program .sh synopsis .nf .br "#define _gnu_source" " /* see feature_test_macros(7) */" .b #include .pp .bi "extern char *" program_invocation_name ; .bi "extern char *" program_invocation_short_name ; .fi .sh description .i program_invocation_name contains the name that was used to invoke the calling program. this is the same as the value of .i argv[0] in .ir main (), with the difference that the scope of .i program_invocation_name is global. .pp .i program_invocation_short_name contains the basename component of name that was used to invoke the calling program. that is, it is the same value as .ir program_invocation_name , with all text up to and including the final slash (/), if any, removed. .pp these variables are automatically initialized by the glibc run-time startup code. .sh conforming to these variables are gnu extensions, and should not be used in programs intended to be portable. .sh notes the linux-specific .i /proc/[number]/cmdline file provides access to similar information. .sh see also .br proc (5) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. \t .\" copyright 2002 walter harms (walter.harms@informatik.uni-oldenburg.de) .\" .\" %%%license_start(gpl_noversion_oneline) .\" distributed under gpl .\" %%%license_end .\" .\" corrected, aeb, 2002-05-30 .\" .th a64l 3 2021-03-22 "" "linux programmer's manual" .sh name a64l, l64a \- convert between long and base-64 .sh synopsis .nf .b #include .pp .bi "long a64l(const char *" str64 ); .bi "char *l64a(long " value ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br a64l (), .br l64a (): .nf _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended || /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _svid_source .fi .sh description these functions provide a conversion between 32-bit long integers and little-endian base-64 ascii strings (of length zero to six). if the string used as argument for .br a64l () has length greater than six, only the first six bytes are used. if the type .i long has more than 32 bits, then .br l64a () uses only the low order 32 bits of .ir value , and .br a64l () sign-extends its 32-bit result. .pp the 64 digits in the base-64 system are: .pp .rs .nf \&\(aq.\(aq represents a 0 \&\(aq/\(aq represents a 1 0-9 represent 2-11 a-z represent 12-37 a-z represent 38-63 .fi .re .pp so 123 = 59*64\(ha0 + 1*64\(ha1 = "v/". .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br l64a () t} thread safety mt-unsafe race:l64a t{ .br a64l () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes the value returned by .br l64a () may be a pointer to a static buffer, possibly overwritten by later calls. .pp the behavior of .br l64a () is undefined when .i value is negative. if .i value is zero, it returns an empty string. .pp these functions are broken in glibc before 2.2.5 (puts most significant digit first). .pp this is not the encoding used by .br uuencode (1). .sh see also .br uuencode (1), .\" .br itoa (3), .br strtoul (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/system_data_types.7 .so man7/system_data_types.7 .so man3/endian.3 .\" this manpage is copyright (c) 1992 drew eckhardt; .\" and copyright (c) 1993 michael haardt, ian jackson. .\" and copyright (c) 2008 greg banks .\" and copyright (c) 2006, 2008, 2013, 2014 michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified 1993-07-21 by rik faith .\" modified 1994-08-21 by michael haardt .\" modified 1996-04-13 by andries brouwer .\" modified 1996-05-13 by thomas koenig .\" modified 1996-12-20 by michael haardt .\" modified 1999-02-19 by andries brouwer .\" modified 1998-11-28 by joseph s. myers .\" modified 1999-06-03 by michael haardt .\" modified 2002-05-07 by michael kerrisk .\" modified 2004-06-23 by michael kerrisk .\" 2004-12-08, mtk, reordered flags list alphabetically .\" 2004-12-08, martin pool (& mtk), added o_noatime .\" 2007-09-18, mtk, added description of o_cloexec + other minor edits .\" 2008-01-03, mtk, with input from trond myklebust .\" and timo sirainen .\" rewrite description of o_excl. .\" 2008-01-11, greg banks : add more detail .\" on o_direct. .\" 2008-02-26, michael haardt: reorganized text for o_creat and mode .\" .\" fixme . apr 08: the next posix revision has o_exec, o_search, and .\" o_ttyinit. eventually these may need to be documented. --mtk .\" .th open 2 2021-08-27 "linux" "linux programmer's manual" .sh name open, openat, creat \- open and possibly create a file .sh synopsis .nf .b #include .pp .bi "int open(const char *" pathname ", int " flags ); .bi "int open(const char *" pathname ", int " flags ", mode_t " mode ); .pp .bi "int creat(const char *" pathname ", mode_t " mode ); .pp .bi "int openat(int " dirfd ", const char *" pathname ", int " flags ); .bi "int openat(int " dirfd ", const char *" pathname ", int " flags \ ", mode_t " mode ); .pp /* documented separately, in \fbopenat2\fp(2): */ .bi "int openat2(int " dirfd ", const char *" pathname , .bi " const struct open_how *" how ", size_t " size ");" .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br openat (): .nf since glibc 2.10: _posix_c_source >= 200809l before glibc 2.10: _atfile_source .fi .sh description the .br open () system call opens the file specified by .ir pathname . if the specified file does not exist, it may optionally (if .b o_creat is specified in .ir flags ) be created by .br open (). .pp the return value of .br open () is a file descriptor, a small, nonnegative integer that is an index to an entry in the process's table of open file descriptors. the file descriptor is used in subsequent system calls .rb ( read "(2), " write "(2), " lseek "(2), " fcntl (2), etc.) to refer to the open file. the file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open for the process. .pp by default, the new file descriptor is set to remain open across an .br execve (2) (i.e., the .b fd_cloexec file descriptor flag described in .br fcntl (2) is initially disabled); the .b o_cloexec flag, described below, can be used to change this default. the file offset is set to the beginning of the file (see .br lseek (2)). .pp a call to .br open () creates a new .ir "open file description" , an entry in the system-wide table of open files. the open file description records the file offset and the file status flags (see below). a file descriptor is a reference to an open file description; this reference is unaffected if .i pathname is subsequently removed or modified to refer to a different file. for further details on open file descriptions, see notes. .pp the argument .i flags must include one of the following .ir "access modes" : .br o_rdonly ", " o_wronly ", or " o_rdwr . these request opening the file read-only, write-only, or read/write, respectively. .pp in addition, zero or more file creation flags and file status flags can be .ri bitwise- or 'd in .ir flags . the .i file creation flags are .br o_cloexec , .br o_creat , .br o_directory , .br o_excl , .br o_noctty , .br o_nofollow , .br o_tmpfile , and .br o_trunc . the .i file status flags are all of the remaining flags listed below. .\" susv4 divides the flags into: .\" * access mode .\" * file creation .\" * file status .\" * other (o_cloexec, o_directory, o_nofollow) .\" though it's not clear what the difference between "other" and .\" "file creation" flags is. i raised an aardvark to see if this .\" can be clarified in susv4; 10 oct 2008. .\" http://thread.gmane.org/gmane.comp.standards.posix.austin.general/64/focus=67 .\" tc1 (balloted in 2013), resolved this, so that those three constants .\" are also categorized" as file status flags. .\" the distinction between these two groups of flags is that the file creation flags affect the semantics of the open operation itself, while the file status flags affect the semantics of subsequent i/o operations. the file status flags can be retrieved and (in some cases) modified; see .br fcntl (2) for details. .pp the full list of file creation flags and file status flags is as follows: .tp .b o_append the file is opened in append mode. before each .br write (2), the file offset is positioned at the end of the file, as if with .br lseek (2). the modification of the file offset and the write operation are performed as a single atomic step. .ip .b o_append may lead to corrupted files on nfs filesystems if more than one process appends data to a file at once. .\" for more background, see .\" http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=453946 .\" http://nfs.sourceforge.net/ this is because nfs does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition. .tp .b o_async enable signal-driven i/o: generate a signal .rb ( sigio by default, but this can be changed via .br fcntl (2)) when input or output becomes possible on this file descriptor. this feature is available only for terminals, pseudoterminals, sockets, and (since linux 2.6) pipes and fifos. see .br fcntl (2) for further details. see also bugs, below. .tp .br o_cloexec " (since linux 2.6.23)" .\" note! several other man pages refer to this text enable the close-on-exec flag for the new file descriptor. .\" fixme . for later review when issue 8 is one day released... .\" posix proposes to fix many apis that provide hidden fds .\" http://austingroupbugs.net/tag_view_page.php?tag_id=8 .\" http://austingroupbugs.net/view.php?id=368 specifying this flag permits a program to avoid additional .br fcntl (2) .b f_setfd operations to set the .b fd_cloexec flag. .ip note that the use of this flag is essential in some multithreaded programs, because using a separate .br fcntl (2) .b f_setfd operation to set the .b fd_cloexec flag does not suffice to avoid race conditions where one thread opens a file descriptor and attempts to set its close-on-exec flag using .br fcntl (2) at the same time as another thread does a .br fork (2) plus .br execve (2). depending on the order of execution, the race may lead to the file descriptor returned by .br open () being unintentionally leaked to the program executed by the child process created by .br fork (2). (this kind of race is in principle possible for any system call that creates a file descriptor whose close-on-exec flag should be set, and various other linux system calls provide an equivalent of the .br o_cloexec flag to deal with this problem.) .\" this flag fixes only one form of the race condition; .\" the race can also occur with, for example, file descriptors .\" returned by accept(), pipe(), etc. .tp .b o_creat if .i pathname does not exist, create it as a regular file. .ip the owner (user id) of the new file is set to the effective user id of the process. .ip the group ownership (group id) of the new file is set either to the effective group id of the process (system v semantics) or to the group id of the parent directory (bsd semantics). on linux, the behavior depends on whether the set-group-id mode bit is set on the parent directory: if that bit is set, then bsd semantics apply; otherwise, system v semantics apply. for some filesystems, the behavior also depends on the .i bsdgroups and .i sysvgroups mount options described in .br mount (8). .\" as at 2.6.25, bsdgroups is supported by ext2, ext3, ext4, and .\" xfs (since 2.6.14). .ip the .i mode argument specifies the file mode bits to be applied when a new file is created. if neither .b o_creat nor .b o_tmpfile is specified in .ir flags , then .i mode is ignored (and can thus be specified as 0, or simply omitted). the .i mode argument .b must be supplied if .b o_creat or .b o_tmpfile is specified in .ir flags ; if it is not supplied, some arbitrary bytes from the stack will be applied as the file mode. .ip the effective mode is modified by the process's .i umask in the usual way: in the absence of a default acl, the mode of the created file is .ir "(mode\ &\ \(tiumask)" . .ip note that .i mode applies only to future accesses of the newly created file; the .br open () call that creates a read-only file may well return a read/write file descriptor. .ip the following symbolic constants are provided for .ir mode : .rs .tp 9 .b s_irwxu 00700 user (file owner) has read, write, and execute permission .tp .b s_irusr 00400 user has read permission .tp .b s_iwusr 00200 user has write permission .tp .b s_ixusr 00100 user has execute permission .tp .b s_irwxg 00070 group has read, write, and execute permission .tp .b s_irgrp 00040 group has read permission .tp .b s_iwgrp 00020 group has write permission .tp .b s_ixgrp 00010 group has execute permission .tp .b s_irwxo 00007 others have read, write, and execute permission .tp .b s_iroth 00004 others have read permission .tp .b s_iwoth 00002 others have write permission .tp .b s_ixoth 00001 others have execute permission .re .ip according to posix, the effect when other bits are set in .i mode is unspecified. on linux, the following bits are also honored in .ir mode : .rs .tp 9 .b s_isuid 0004000 set-user-id bit .tp .b s_isgid 0002000 set-group-id bit (see .br inode (7)). .tp .b s_isvtx 0001000 sticky bit (see .br inode (7)). .re .tp .br o_direct " (since linux 2.4.10)" try to minimize cache effects of the i/o to and from this file. in general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. file i/o is done directly to/from user-space buffers. the .b o_direct flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the .b o_sync flag that data and necessary metadata are transferred. to guarantee synchronous i/o, .b o_sync must be used in addition to .br o_direct . see notes below for further discussion. .ip a semantically similar (but deprecated) interface for block devices is described in .br raw (8). .tp .b o_directory if \fipathname\fp is not a directory, cause the open to fail. .\" but see the following and its replies: .\" http://marc.theaimsgroup.com/?t=112748702800001&r=1&w=2 .\" [patch] open: o_directory and o_creat together should fail .\" o_directory | o_creat causes o_directory to be ignored. this flag was added in kernel version 2.1.126, to avoid denial-of-service problems if .br opendir (3) is called on a fifo or tape device. .tp .b o_dsync write operations on the file will complete according to the requirements of synchronized i/o .i data integrity completion. .ip by the time .br write (2) (and similar) return, the output data has been transferred to the underlying hardware, along with any file metadata that would be required to retrieve that data (i.e., as though each .br write (2) was followed by a call to .br fdatasync (2)). .ir "see notes below" . .tp .b o_excl ensure that this call creates the file: if this flag is specified in conjunction with .br o_creat , and .i pathname already exists, then .br open () fails with the error .br eexist . .ip when these two flags are specified, symbolic links are not followed: .\" posix.1-2001 explicitly requires this behavior. if .i pathname is a symbolic link, then .br open () fails regardless of where the symbolic link points. .ip in general, the behavior of .b o_excl is undefined if it is used without .br o_creat . there is one exception: on linux 2.6 and later, .b o_excl can be used without .b o_creat if .i pathname refers to a block device. if the block device is in use by the system (e.g., mounted), .br open () fails with the error .br ebusy . .ip on nfs, .b o_excl is supported only when using nfsv3 or later on kernel 2.6 or later. in nfs environments where .b o_excl support is not provided, programs that rely on it for performing locking tasks will contain a race condition. portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on nfs support for .br o_excl , can create a unique file on the same filesystem (e.g., incorporating hostname and pid), and use .br link (2) to make a link to the lockfile. if .br link (2) returns 0, the lock is successful. otherwise, use .br stat (2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful. .tp .b o_largefile (lfs) allow files whose sizes cannot be represented in an .i off_t (but can be represented in an .ir off64_t ) to be opened. the .b _largefile64_source macro must be defined (before including .i any header files) in order to obtain this definition. setting the .b _file_offset_bits feature test macro to 64 (rather than using .br o_largefile ) is the preferred method of accessing large files on 32-bit systems (see .br feature_test_macros (7)). .tp .br o_noatime " (since linux 2.6.8)" do not update the file last access time .ri ( st_atime in the inode) when the file is .br read (2). .ip this flag can be employed only if one of the following conditions is true: .rs .ip * 3 the effective uid of the process .\" strictly speaking: the filesystem uid matches the owner uid of the file. .ip * the calling process has the .br cap_fowner capability in its user namespace and the owner uid of the file has a mapping in the namespace. .re .ip this flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. this flag may not be effective on all filesystems. one example is nfs, where the server maintains the access time. .\" the o_noatime flag also affects the treatment of st_atime .\" by mmap() and readdir(2), mtk, dec 04. .tp .b o_noctty if .i pathname refers to a terminal device\(emsee .br tty (4)\(emit will not become the process's controlling terminal even if the process does not have one. .tp .b o_nofollow if the trailing component (i.e., basename) of .i pathname is a symbolic link, then the open fails, with the error .br eloop . symbolic links in earlier components of the pathname will still be followed. (note that the .b eloop error that can occur in this case is indistinguishable from the case where an open fails because there are too many symbolic links found while resolving components in the prefix part of the pathname.) .ip this flag is a freebsd extension, which was added to linux in version 2.1.126, and has subsequently been standardized in posix.1-2008. .ip see also .br o_path below. .\" the headers from glibc 2.0.100 and later include a .\" definition of this flag; \fikernels before 2.1.126 will ignore it if .\" used\fp. .tp .br o_nonblock " or " o_ndelay when possible, the file is opened in nonblocking mode. neither the .br open () nor any subsequent i/o operations on the file descriptor which is returned will cause the calling process to wait. .ip note that the setting of this flag has no effect on the operation of .br poll (2), .br select (2), .br epoll (7), and similar, since those interfaces merely inform the caller about whether a file descriptor is "ready", meaning that an i/o operation performed on the file descriptor with the .b o_nonblock flag .i clear would not block. .ip note that this flag has no effect for regular files and block devices; that is, i/o operations will (briefly) block when device activity is required, regardless of whether .b o_nonblock is set. since .b o_nonblock semantics might eventually be implemented, applications should not depend upon blocking behavior when specifying this flag for regular files and block devices. .ip for the handling of fifos (named pipes), see also .br fifo (7). for a discussion of the effect of .b o_nonblock in conjunction with mandatory file locks and with file leases, see .br fcntl (2). .tp .br o_path " (since linux 2.6.39)" .\" commit 1abf0c718f15a56a0a435588d1b104c7a37dc9bd .\" commit 326be7b484843988afe57566b627fb7a70beac56 .\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d .\" .\" http://thread.gmane.org/gmane.linux.man/2790/focus=3496 .\" subject: re: [patch] open(2): document o_path .\" newsgroups: gmane.linux.man, gmane.linux.kernel .\" obtain a file descriptor that can be used for two purposes: to indicate a location in the filesystem tree and to perform operations that act purely at the file descriptor level. the file itself is not opened, and other file operations (e.g., .br read (2), .br write (2), .br fchmod (2), .br fchown (2), .br fgetxattr (2), .br ioctl (2), .br mmap (2)) fail with the error .br ebadf . .ip the following operations .i can be performed on the resulting file descriptor: .rs .ip * 3 .br close (2). .ip * .br fchdir (2), if the file descriptor refers to a directory (since linux 3.5). .\" commit 332a2e1244bd08b9e3ecd378028513396a004a24 .ip * .br fstat (2) (since linux 3.6). .ip * .\" fstat(): commit 55815f70147dcfa3ead5738fd56d3574e2e3c1c2 .br fstatfs (2) (since linux 3.12). .\" fstatfs(): commit 9d05746e7b16d8565dddbe3200faa1e669d23bbf .ip * duplicating the file descriptor .rb ( dup (2), .br fcntl (2) .br f_dupfd , etc.). .ip * getting and setting file descriptor flags .rb ( fcntl (2) .br f_getfd and .br f_setfd ). .ip * retrieving open file status flags using the .br fcntl (2) .br f_getfl operation: the returned flags will include the bit .br o_path . .ip * passing the file descriptor as the .ir dirfd argument of .br openat () and the other "*at()" system calls. this includes .br linkat (2) with .br at_empty_path (or via procfs using .br at_symlink_follow ) even if the file is not a directory. .ip * passing the file descriptor to another process via a unix domain socket (see .br scm_rights in .br unix (7)). .re .ip when .b o_path is specified in .ir flags , flag bits other than .br o_cloexec , .br o_directory , and .br o_nofollow are ignored. .ip opening a file or directory with the .b o_path flag requires no permissions on the object itself (but does require execute permission on the directories in the path prefix). depending on the subsequent operation, a check for suitable file permissions may be performed (e.g., .br fchdir (2) requires execute permission on the directory referred to by its file descriptor argument). by contrast, obtaining a reference to a filesystem object by opening it with the .b o_rdonly flag requires that the caller have read permission on the object, even when the subsequent operation (e.g., .br fchdir (2), .br fstat (2)) does not require read permission on the object. .ip if .i pathname is a symbolic link and the .br o_nofollow flag is also specified, then the call returns a file descriptor referring to the symbolic link. this file descriptor can be used as the .i dirfd argument in calls to .br fchownat (2), .br fstatat (2), .br linkat (2), and .br readlinkat (2) with an empty pathname to have the calls operate on the symbolic link. .ip if .i pathname refers to an automount point that has not yet been triggered, so no other filesystem is mounted on it, then the call returns a file descriptor referring to the automount directory without triggering a mount. .br fstatfs (2) can then be used to determine if it is, in fact, an untriggered automount point .rb ( ".f_type == autofs_super_magic" ). .ip one use of .b o_path for regular files is to provide the equivalent of posix.1's .b o_exec functionality. this permits us to open a file for which we have execute permission but not read permission, and then execute that file, with steps something like the following: .ip .in +4n .ex char buf[path_max]; fd = open("some_prog", o_path); snprintf(buf, path_max, "/proc/self/fd/%d", fd); execl(buf, "some_prog", (char *) null); .ee .in .ip an .b o_path file descriptor can also be passed as the argument of .br fexecve (3). .tp .b o_sync write operations on the file will complete according to the requirements of synchronized i/o .i file integrity completion (by contrast with the synchronized i/o .i data integrity completion provided by .br o_dsync .) .ip by the time .br write (2) (or similar) returns, the output data and associated file metadata have been transferred to the underlying hardware (i.e., as though each .br write (2) was followed by a call to .br fsync (2)). .ir "see notes below" . .tp .br o_tmpfile " (since linux 3.11)" .\" commit 60545d0d4610b02e55f65d141c95b18ccf855b6e .\" commit f4e0c30c191f87851c4a53454abb55ee276f4a7e .\" commit bb458c644a59dbba3a1fe59b27106c5e68e1c4bd create an unnamed temporary regular file. the .i pathname argument specifies a directory; an unnamed inode will be created in that directory's filesystem. anything written to the resulting file will be lost when the last file descriptor is closed, unless the file is given a name. .ip .b o_tmpfile must be specified with one of .b o_rdwr or .b o_wronly and, optionally, .br o_excl . if .b o_excl is not specified, then .br linkat (2) can be used to link the temporary file into the filesystem, making it permanent, using code like the following: .ip .in +4n .ex char path[path_max]; fd = open("/path/to/dir", o_tmpfile | o_rdwr, s_irusr | s_iwusr); /* file i/o on \(aqfd\(aq... */ linkat(fd, "", at_fdcwd, "/path/for/file", at_empty_path); /* if the caller doesn\(aqt have the cap_dac_read_search capability (needed to use at_empty_path with linkat(2)), and there is a proc(5) filesystem mounted, then the linkat(2) call above can be replaced with: snprintf(path, path_max, "/proc/self/fd/%d", fd); linkat(at_fdcwd, path, at_fdcwd, "/path/for/file", at_symlink_follow); */ .ee .in .ip in this case, the .br open () .i mode argument determines the file permission mode, as with .br o_creat . .ip specifying .b o_excl in conjunction with .b o_tmpfile prevents a temporary file from being linked into the filesystem in the above manner. (note that the meaning of .b o_excl in this case is different from the meaning of .b o_excl otherwise.) .ip there are two main use cases for .\" inspired by http://lwn.net/articles/559147/ .br o_tmpfile : .rs .ip * 3 improved .br tmpfile (3) functionality: race-free creation of temporary files that (1) are automatically deleted when closed; (2) can never be reached via any pathname; (3) are not subject to symlink attacks; and (4) do not require the caller to devise unique names. .ip * creating a file that is initially invisible, which is then populated with data and adjusted to have appropriate filesystem attributes .rb ( fchown (2), .br fchmod (2), .br fsetxattr (2), etc.) before being atomically linked into the filesystem in a fully formed state (using .br linkat (2) as described above). .re .ip .b o_tmpfile requires support by the underlying filesystem; only a subset of linux filesystems provide that support. in the initial implementation, support was provided in the ext2, ext3, ext4, udf, minix, and tmpfs filesystems. .\" to check for support, grep for "tmpfile" in kernel sources support for other filesystems has subsequently been added as follows: xfs (linux 3.15); .\" commit 99b6436bc29e4f10e4388c27a3e4810191cc4788 .\" commit ab29743117f9f4c22ac44c13c1647fb24fb2bafe btrfs (linux 3.16); .\" commit ef3b9af50bfa6a1f02cd7b3f5124b712b1ba3e3c f2fs (linux 3.16); .\" commit 50732df02eefb39ab414ef655979c2c9b64ad21c and ubifs (linux 4.9) .tp .b o_trunc if the file already exists and is a regular file and the access mode allows writing (i.e., is .b o_rdwr or .br o_wronly ) it will be truncated to length 0. if the file is a fifo or terminal device file, the .b o_trunc flag is ignored. otherwise, the effect of .b o_trunc is unspecified. .ss creat() a call to .br creat () is equivalent to calling .br open () with .i flags equal to .br o_creat|o_wronly|o_trunc . .ss openat() the .br openat () system call operates in exactly the same way as .br open (), except for the differences described here. .pp the .i dirfd argument is used in conjunction with the .i pathname argument as follows: .ip * 3 if the pathname given in .i pathname is absolute, then .i dirfd is ignored. .ip * if the pathname given in .i pathname is relative and .i dirfd is the special value .br at_fdcwd , then .i pathname is interpreted relative to the current working directory of the calling process (like .br open ()). .ip * if the pathname given in .i pathname is relative, then it is interpreted relative to the directory referred to by the file descriptor .i dirfd (rather than relative to the current working directory of the calling process, as is done by .br open () for a relative pathname). in this case, .i dirfd must be a directory that was opened for reading .rb ( o_rdonly ) or using the .b o_path flag. .pp if the pathname given in .i pathname is relative, and .i dirfd is not a valid file descriptor, an error .rb ( ebadf ) results. (specifying an invalid file descriptor number in .i dirfd can be used as a means to ensure that .i pathname is absolute.) .\" .ss openat2(2) the .br openat2 (2) system call is an extension of .br openat (), and provides a superset of the features of .br openat (). it is documented separately, in .br openat2 (2). .sh return value on success, .br open (), .br openat (), and .br creat () return the new file descriptor (a nonnegative integer). on error, \-1 is returned and .i errno is set to indicate the error. .sh errors .br open (), .br openat (), and .br creat () can fail with the following errors: .tp .b eacces the requested access to the file is not allowed, or search permission is denied for one of the directories in the path prefix of .ir pathname , or the file did not exist yet and write access to the parent directory is not allowed. (see also .br path_resolution (7).) .tp .b eacces .\" commit 30aba6656f61ed44cba445a3c0d38b296fa9e8f5 where .b o_creat is specified, the .i protected_fifos or .i protected_regular sysctl is enabled, the file already exists and is a fifo or regular file, the owner of the file is neither the current user nor the owner of the containing directory, and the containing directory is both world- or group-writable and sticky. for details, see the descriptions of .ir /proc/sys/fs/protected_fifos and .ir /proc/sys/fs/protected_regular in .br proc (5). .tp .b ebadf .rb ( openat ()) .i pathname is relative but .i dirfd is neither .b at_fdcwd nor a valid file descriptor. .tp .b ebusy .b o_excl was specified in .i flags and .i pathname refers to a block device that is in use by the system (e.g., it is mounted). .tp .b edquot where .b o_creat is specified, the file does not exist, and the user's quota of disk blocks or inodes on the filesystem has been exhausted. .tp .b eexist .i pathname already exists and .br o_creat " and " o_excl were used. .tp .b efault .i pathname points outside your accessible address space. .tp .b efbig see .br eoverflow . .tp .b eintr while blocked waiting to complete an open of a slow device (e.g., a fifo; see .br fifo (7)), the call was interrupted by a signal handler; see .br signal (7). .tp .b einval the filesystem does not support the .br o_direct flag. see .br notes for more information. .tp .b einval invalid value in .\" in particular, __o_tmpfile instead of o_tmpfile .ir flags . .tp .b einval .b o_tmpfile was specified in .ir flags , but neither .b o_wronly nor .b o_rdwr was specified. .tp .b einval .b o_creat was specified in .i flags and the final component ("basename") of the new file's .i pathname is invalid (e.g., it contains characters not permitted by the underlying filesystem). .tp .b einval the final component ("basename") of .i pathname is invalid (e.g., it contains characters not permitted by the underlying filesystem). .tp .b eisdir .i pathname refers to a directory and the access requested involved writing (that is, .b o_wronly or .b o_rdwr is set). .tp .b eisdir .i pathname refers to an existing directory, .b o_tmpfile and one of .b o_wronly or .b o_rdwr were specified in .ir flags , but this kernel version does not provide the .b o_tmpfile functionality. .tp .b eloop too many symbolic links were encountered in resolving .ir pathname . .tp .b eloop .i pathname was a symbolic link, and .i flags specified .br o_nofollow but not .br o_path . .tp .b emfile the per-process limit on the number of open file descriptors has been reached (see the description of .br rlimit_nofile in .br getrlimit (2)). .tp .b enametoolong .i pathname was too long. .tp .b enfile the system-wide limit on the total number of open files has been reached. .tp .b enodev .i pathname refers to a device special file and no corresponding device exists. (this is a linux kernel bug; in this situation .b enxio must be returned.) .tp .b enoent .b o_creat is not set and the named file does not exist. .tp .b enoent a directory component in .i pathname does not exist or is a dangling symbolic link. .tp .b enoent .i pathname refers to a nonexistent directory, .b o_tmpfile and one of .b o_wronly or .b o_rdwr were specified in .ir flags , but this kernel version does not provide the .b o_tmpfile functionality. .tp .b enomem the named file is a fifo, but memory for the fifo buffer can't be allocated because the per-user hard limit on memory allocation for pipes has been reached and the caller is not privileged; see .br pipe (7). .tp .b enomem insufficient kernel memory was available. .tp .b enospc .i pathname was to be created but the device containing .i pathname has no room for the new file. .tp .b enotdir a component used as a directory in .i pathname is not, in fact, a directory, or \fbo_directory\fp was specified and .i pathname was not a directory. .tp .b enotdir .rb ( openat ()) .i pathname is a relative pathname and .i dirfd is a file descriptor referring to a file other than a directory. .tp .b enxio .br o_nonblock " | " o_wronly is set, the named file is a fifo, and no process has the fifo open for reading. .tp .b enxio the file is a device special file and no corresponding device exists. .tp .b enxio the file is a unix domain socket. .tp .br eopnotsupp the filesystem containing .i pathname does not support .br o_tmpfile . .tp .b eoverflow .i pathname refers to a regular file that is too large to be opened. the usual scenario here is that an application compiled on a 32-bit platform without .i \-d_file_offset_bits=64 tried to open a file whose size exceeds .i (1<<31)\-1 bytes; see also .b o_largefile above. this is the error specified by posix.1; in kernels before 2.6.24, linux gave the error .b efbig for this case. .\" see http://bugzilla.kernel.org/show_bug.cgi?id=7253 .\" "open of a large file on 32-bit fails with efbig, should be eoverflow" .\" reported 2006-10-03 .tp .b eperm the .b o_noatime flag was specified, but the effective user id of the caller .\" strictly speaking, it's the filesystem uid... (mtk) did not match the owner of the file and the caller was not privileged. .tp .b eperm the operation was prevented by a file seal; see .br fcntl (2). .tp .b erofs .i pathname refers to a file on a read-only filesystem and write access was requested. .tp .b etxtbsy .i pathname refers to an executable image which is currently being executed and write access was requested. .tp .b etxtbsy .i pathname refers to a file that is currently in use as a swap file, and the .b o_trunc flag was specified. .tp .b etxtbsy .i pathname refers to a file that is currently being read by the kernel (e.g., for module/firmware loading), and write access was requested. .tp .b ewouldblock the .b o_nonblock flag was specified, and an incompatible lease was held on the file (see .br fcntl (2)). .sh versions .br openat () was added to linux in kernel 2.6.16; library support was added to glibc in version 2.4. .sh conforming to .br open (), .br creat () svr4, 4.3bsd, posix.1-2001, posix.1-2008. .pp .br openat (): posix.1-2008. .pp .br openat2 (2) is linux-specific. .pp the .br o_direct , .br o_noatime , .br o_path , and .br o_tmpfile flags are linux-specific. one must define .b _gnu_source to obtain their definitions. .pp the .br o_cloexec , .br o_directory , and .br o_nofollow flags are not specified in posix.1-2001, but are specified in posix.1-2008. since glibc 2.12, one can obtain their definitions by defining either .b _posix_c_source with a value greater than or equal to 200809l or .br _xopen_source with a value greater than or equal to 700. in glibc 2.11 and earlier, one obtains the definitions by defining .br _gnu_source . .pp as noted in .br feature_test_macros (7), feature test macros such as .br _posix_c_source , .br _xopen_source , and .b _gnu_source must be defined before including .i any header files. .sh notes under linux, the .b o_nonblock flag is sometimes used in cases where one wants to open but does not necessarily have the intention to read or write. for example, this may be used to open a device in order to get a file descriptor for use with .br ioctl (2). .pp the (undefined) effect of .b o_rdonly | o_trunc varies among implementations. on many systems the file is actually truncated. .\" linux 2.0, 2.5: truncate .\" solaris 5.7, 5.8: truncate .\" irix 6.5: truncate .\" tru64 5.1b: truncate .\" hp-ux 11.22: truncate .\" freebsd 4.7: truncate .pp note that .br open () can open device special files, but .br creat () cannot create them; use .br mknod (2) instead. .pp if the file is newly created, its .ir st_atime , .ir st_ctime , .i st_mtime fields (respectively, time of last access, time of last status change, and time of last modification; see .br stat (2)) are set to the current time, and so are the .i st_ctime and .i st_mtime fields of the parent directory. otherwise, if the file is modified because of the .b o_trunc flag, its .i st_ctime and .i st_mtime fields are set to the current time. .pp the files in the .i /proc/[pid]/fd directory show the open file descriptors of the process with the pid .ir pid . the files in the .i /proc/[pid]/fdinfo directory show even more information about these file descriptors. see .br proc (5) for further details of both of these directories. .pp the linux header file .b doesn't define .br o_async ; the (bsd-derived) .b fasync synonym is defined instead. .\" .\" .ss open file descriptions the term open file description is the one used by posix to refer to the entries in the system-wide table of open files. in other contexts, this object is variously also called an "open file object", a "file handle", an "open file table entry", or\(emin kernel-developer parlance\(ema .ir "struct file" . .pp when a file descriptor is duplicated (using .br dup (2) or similar), the duplicate refers to the same open file description as the original file descriptor, and the two file descriptors consequently share the file offset and file status flags. such sharing can also occur between processes: a child process created via .br fork (2) inherits duplicates of its parent's file descriptors, and those duplicates refer to the same open file descriptions. .pp each .br open () of a file creates a new open file description; thus, there may be multiple open file descriptions corresponding to a file inode. .pp on linux, one can use the .br kcmp (2) .b kcmp_file operation to test whether two file descriptors (in the same process or in two different processes) refer to the same open file description. .\" .\" .ss synchronized i/o the posix.1-2008 "synchronized i/o" option specifies different variants of synchronized i/o, and specifies the .br open () flags .br o_sync , .br o_dsync , and .br o_rsync for controlling the behavior. regardless of whether an implementation supports this option, it must at least support the use of .br o_sync for regular files. .pp linux implements .br o_sync and .br o_dsync , but not .br o_rsync . somewhat incorrectly, glibc defines .br o_rsync to have the same value as .br o_sync . .rb ( o_rsync is defined in the linux header file .i on hp pa-risc, but it is not used.) .pp .br o_sync provides synchronized i/o .i file integrity completion, meaning write operations will flush data and all associated metadata to the underlying hardware. .br o_dsync provides synchronized i/o .i data integrity completion, meaning write operations will flush data to the underlying hardware, but will only flush metadata updates that are required to allow a subsequent read operation to complete successfully. data integrity completion can reduce the number of disk operations that are required for applications that don't need the guarantees of file integrity completion. .pp to understand the difference between the two types of completion, consider two pieces of file metadata: the file last modification timestamp .ri ( st_mtime ) and the file length. all write operations will update the last file modification timestamp, but only writes that add data to the end of the file will change the file length. the last modification timestamp is not needed to ensure that a read completes successfully, but the file length is. thus, .br o_dsync would only guarantee to flush updates to the file length metadata (whereas .br o_sync would also always flush the last modification timestamp metadata). .pp before linux 2.6.33, linux implemented only the .br o_sync flag for .br open (). however, when that flag was specified, most filesystems actually provided the equivalent of synchronized i/o .i data integrity completion (i.e., .br o_sync was actually implemented as the equivalent of .br o_dsync ). .pp since linux 2.6.33, proper .br o_sync support is provided. however, to ensure backward binary compatibility, .br o_dsync was defined with the same value as the historical .br o_sync , and .br o_sync was defined as a new (two-bit) flag value that includes the .br o_dsync flag value. this ensures that applications compiled against new headers get at least .br o_dsync semantics on pre-2.6.33 kernels. .\" .ss c library/kernel differences since version 2.26, the glibc wrapper function for .br open () employs the .br openat () system call, rather than the kernel's .br open () system call. for certain architectures, this is also true in glibc versions before 2.26. .\" .ss nfs there are many infelicities in the protocol underlying nfs, affecting amongst others .br o_sync " and " o_ndelay . .pp on nfs filesystems with uid mapping enabled, .br open () may return a file descriptor but, for example, .br read (2) requests are denied with \fbeacces\fp. this is because the client performs .br open () by checking the permissions, but uid mapping is performed by the server upon read and write requests. .\" .\" .ss fifos opening the read or write end of a fifo blocks until the other end is also opened (by another process or thread). see .br fifo (7) for further details. .\" .\" .ss file access mode unlike the other values that can be specified in .ir flags , the .i "access mode" values .br o_rdonly ", " o_wronly ", and " o_rdwr do not specify individual bits. rather, they define the low order two bits of .ir flags , and are defined respectively as 0, 1, and 2. in other words, the combination .b "o_rdonly | o_wronly" is a logical error, and certainly does not have the same meaning as .br o_rdwr . .pp linux reserves the special, nonstandard access mode 3 (binary 11) in .i flags to mean: check for read and write permission on the file and return a file descriptor that can't be used for reading or writing. this nonstandard access mode is used by some linux drivers to return a file descriptor that is to be used only for device-specific .br ioctl (2) operations. .\" see for example util-linux's disk-utils/setfdprm.c .\" for some background on access mode 3, see .\" http://thread.gmane.org/gmane.linux.kernel/653123 .\" "[rfc] correct flags to f_mode conversion in __dentry_open" .\" lkml, 12 mar 2008 .\" .\" .ss rationale for openat() and other "directory file descriptor" apis .br openat () and the other system calls and library functions that take a directory file descriptor argument (i.e., .br execveat (2), .br faccessat (2), .br fanotify_mark (2), .br fchmodat (2), .br fchownat (2), .br fspick (2), .br fstatat (2), .br futimesat (2), .br linkat (2), .br mkdirat (2), .br mknodat (2), .br mount_setattr (2), .br move_mount (2), .br name_to_handle_at (2), .br open_tree (2), .br openat2 (2), .br readlinkat (2), .br renameat (2), .br renameat2 (2), .br statx (2), .br symlinkat (2), .br unlinkat (2), .br utimensat (2), .br mkfifoat (3), and .br scandirat (3)) address two problems with the older interfaces that preceded them. here, the explanation is in terms of the .br openat () call, but the rationale is analogous for the other interfaces. .pp first, .br openat () allows an application to avoid race conditions that could occur when using .br open () to open files in directories other than the current working directory. these race conditions result from the fact that some component of the directory prefix given to .br open () could be changed in parallel with the call to .br open (). suppose, for example, that we wish to create the file .i dir1/dir2/xxx.dep if the file .i dir1/dir2/xxx exists. the problem is that between the existence check and the file-creation step, .i dir1 or .i dir2 (which might be symbolic links) could be modified to point to a different location. such races can be avoided by opening a file descriptor for the target directory, and then specifying that file descriptor as the .i dirfd argument of (say) .br fstatat (2) and .br openat (). the use of the .i dirfd file descriptor also has other benefits: .ip * 3 the file descriptor is a stable reference to the directory, even if the directory is renamed; and .ip * the open file descriptor prevents the underlying filesystem from being dismounted, just as when a process has a current working directory on a filesystem. .pp second, .br openat () allows the implementation of a per-thread "current working directory", via file descriptor(s) maintained by the application. (this functionality can also be obtained by tricks based on the use of .ir /proc/self/fd/ dirfd, but less efficiently.) .pp the .i dirfd argument for these apis can be obtained by using .br open () or .br openat () to open a directory (with either the .br o_rdonly or the .br o_path flag). alternatively, such a file descriptor can be obtained by applying .br dirfd (3) to a directory stream created using .br opendir (3). .pp when these apis are given a .i dirfd argument of .br at_fdcwd or the specified pathname is absolute, then they handle their pathname argument in the same way as the corresponding conventional apis. however, in this case, several of the apis have a .i flags argument that provides access to functionality that is not available with the corresponding conventional apis. .\" .\" .ss o_direct the .b o_direct flag may impose alignment restrictions on the length and address of user-space buffers and the file offset of i/os. in linux alignment restrictions vary by filesystem and kernel version and might be absent entirely. however there is currently no filesystem\-independent interface for an application to discover these restrictions for a given file or filesystem. some filesystems provide their own interfaces for doing so, for example the .b xfs_ioc_dioinfo operation in .br xfsctl (3). .pp under linux 2.4, transfer sizes, the alignment of the user buffer, and the file offset must all be multiples of the logical block size of the filesystem. since linux 2.6.0, alignment to the logical block size of the underlying storage (typically 512 bytes) suffices. the logical block size can be determined using the .br ioctl (2) .b blksszget operation or from the shell using the command: .pp .in +4n .ex blockdev \-\-getss .ee .in .pp .b o_direct i/os should never be run concurrently with the .br fork (2) system call, if the memory buffer is a private mapping (i.e., any mapping created with the .br mmap (2) .br map_private flag; this includes memory allocated on the heap and statically allocated buffers). any such i/os, whether submitted via an asynchronous i/o interface or from another thread in the process, should be completed before .br fork (2) is called. failure to do so can result in data corruption and undefined behavior in parent and child processes. this restriction does not apply when the memory buffer for the .b o_direct i/os was created using .br shmat (2) or .br mmap (2) with the .b map_shared flag. nor does this restriction apply when the memory buffer has been advised as .b madv_dontfork with .br madvise (2), ensuring that it will not be available to the child after .br fork (2). .pp the .b o_direct flag was introduced in sgi irix, where it has alignment restrictions similar to those of linux 2.4. irix has also a .br fcntl (2) call to query appropriate alignments, and sizes. freebsd 4.x introduced a flag of the same name, but without alignment restrictions. .pp .b o_direct support was added under linux in kernel version 2.4.10. older linux kernels simply ignore this flag. some filesystems may not implement the flag, in which case .br open () fails with the error .b einval if it is used. .pp applications should avoid mixing .b o_direct and normal i/o to the same file, and especially to overlapping byte regions in the same file. even when the filesystem correctly handles the coherency issues in this situation, overall i/o throughput is likely to be slower than using either mode alone. likewise, applications should avoid mixing .br mmap (2) of files with direct i/o to the same files. .pp the behavior of .b o_direct with nfs will differ from local filesystems. older kernels, or kernels configured in certain ways, may not support this combination. the nfs protocol does not support passing the flag to the server, so .b o_direct i/o will bypass the page cache only on the client; the server may still cache the i/o. the client asks the server to make the i/o synchronous to preserve the synchronous semantics of .br o_direct . some servers will perform poorly under these circumstances, especially if the i/o size is small. some servers may also be configured to lie to clients about the i/o having reached stable storage; this will avoid the performance penalty at some risk to data integrity in the event of server power failure. the linux nfs client places no alignment restrictions on .b o_direct i/o. .pp in summary, .b o_direct is a potentially powerful tool that should be used with caution. it is recommended that applications treat use of .b o_direct as a performance option which is disabled by default. .sh bugs currently, it is not possible to enable signal-driven i/o by specifying .b o_async when calling .br open (); use .br fcntl (2) to enable this flag. .\" fixme . check bugzilla report on open(o_async) .\" see http://bugzilla.kernel.org/show_bug.cgi?id=5993 .pp one must check for two different error codes, .b eisdir and .br enoent , when trying to determine whether the kernel supports .b o_tmpfile functionality. .pp when both .b o_creat and .b o_directory are specified in .ir flags and the file specified by .i pathname does not exist, .br open () will create a regular file (i.e., .b o_directory is ignored). .sh see also .br chmod (2), .br chown (2), .br close (2), .br dup (2), .br fcntl (2), .br link (2), .br lseek (2), .br mknod (2), .br mmap (2), .br mount (2), .br open_by_handle_at (2), .br openat2 (2), .br read (2), .br socket (2), .br stat (2), .br umask (2), .br unlink (2), .br write (2), .br fopen (3), .br acl (5), .br fifo (7), .br inode (7), .br path_resolution (7), .br symlink (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-13.7 .so man3/endian.3 .\" copyright 1991 the regents of the university of california. .\" all rights reserved. .\" .\" %%%license_start(bsd_4_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. all advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" this product includes software developed by the university of .\" california, berkeley and its contributors. .\" 4. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" @(#)popen.3 6.4 (berkeley) 4/30/91 .\" .\" converted for linux, mon nov 29 14:45:38 1993, faith@cs.unc.edu .\" modified sat may 18 20:37:44 1996 by martin schulze (joey@linux.de) .\" modified 7 may 1998 by joseph s. myers (jsm28@cam.ac.uk) .\" .th popen 3 2021-03-22 "gnu" "linux programmer's manual" .sh name popen, pclose \- pipe stream to or from a process .sh synopsis .nf .b #include .pp .bi "file *popen(const char *" command ", const char *" type ); .bi "int pclose(file *" stream ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br popen (), .br pclose (): .nf _posix_c_source >= 2 || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description the .br popen () function opens a process by creating a pipe, forking, and invoking the shell. since a pipe is by definition unidirectional, the .i type argument may specify only reading or writing, not both; the resulting stream is correspondingly read-only or write-only. .pp the .i command argument is a pointer to a null-terminated string containing a shell command line. this command is passed to .i /bin/sh using the .b \-c flag; interpretation, if any, is performed by the shell. .pp the .i type argument is a pointer to a null-terminated string which must contain either the letter \(aqr\(aq for reading or the letter \(aqw\(aq for writing. since glibc 2.9, this argument can additionally include the letter \(aqe\(aq, which causes the close-on-exec flag .rb ( fd_cloexec ) to be set on the underlying file descriptor; see the description of the .b o_cloexec flag in .br open (2) for reasons why this may be useful. .pp the return value from .br popen () is a normal standard i/o stream in all respects save that it must be closed with .br pclose () rather than .br fclose (3). writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the process that called .br popen (), unless this is altered by the command itself. conversely, reading from the stream reads the command's standard output, and the command's standard input is the same as that of the process that called .br popen (). .pp note that output .br popen () streams are block buffered by default. .pp the .br pclose () function waits for the associated process to terminate and returns the exit status of the command as returned by .br wait4 (2). .sh return value .br popen (): on success, returns a pointer to an open stream that can be used to read or write to the pipe; if the .br fork (2) or .br pipe (2) calls fail, or if the function cannot allocate memory, null is returned. .pp .br pclose (): on success, returns the exit status of the command; if .\" these conditions actually give undefined results, so i commented .\" them out. .\" .i stream .\" is not associated with a "popen()ed" command, if .\".i stream .\" already "pclose()d", or if .br wait4 (2) returns an error, or some other error is detected, \-1 is returned. .pp on failure, both functions set .i errno to indicate the error. .sh errors the .br popen () function does not set .i errno if memory allocation fails. if the underlying .br fork (2) or .br pipe (2) fails, .i errno is set to indicate the error. if the .i type argument is invalid, and this condition is detected, .i errno is set to .br einval . .pp if .br pclose () cannot obtain the child status, .i errno is set to .br echild . .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br popen (), .br pclose () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .pp the \(aqe\(aq value for .i type is a linux extension. .sh notes .br note : carefully read caveats in .br system (3). .sh bugs since the standard input of a command opened for reading shares its seek offset with the process that called .br popen (), if the original process has done a buffered read, the command's input position may not be as expected. similarly, the output from a command opened for writing may become intermingled with that of the original process. the latter can be avoided by calling .br fflush (3) before .br popen (). .pp failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. the only hint is an exit status of 127. .\" .sh history .\" a .\" .br popen () .\" and a .\" .br pclose () .\" function appeared in version 7 at&t unix. .sh see also .br sh (1), .br fork (2), .br pipe (2), .br wait4 (2), .br fclose (3), .br fflush (3), .br fopen (3), .br stdio (3), .br system (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2003 andries brouwer (aeb@cwi.nl) .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .th ualarm 3 2021-03-22 "" "linux programmer's manual" .sh name ualarm \- schedule signal after given number of microseconds .sh synopsis .nf .b "#include " .pp .bi "useconds_t ualarm(useconds_t " usecs ", useconds_t " interval ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br ualarm (): .nf since glibc 2.12: (_xopen_source >= 500) && ! (_posix_c_source >= 200809l) || /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source before glibc 2.12: _bsd_source || _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended .fi .sh description the .br ualarm () function causes the signal .b sigalrm to be sent to the invoking process after (not less than) .i usecs microseconds. the delay may be lengthened slightly by any system activity or by the time spent processing the call or by the granularity of system timers. .pp unless caught or ignored, the .b sigalrm signal will terminate the process. .pp if the .i interval argument is nonzero, further .b sigalrm signals will be sent every .i interval microseconds after the first. .sh return value this function returns the number of microseconds remaining for any alarm that was previously set, or 0 if no alarm was pending. .sh errors .tp .b eintr interrupted by a signal; see .br signal (7). .tp .b einval \fiusecs\fp or \fiinterval\fp is not smaller than 1000000. (on systems where that is considered an error.) .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br ualarm () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to 4.3bsd, posix.1-2001. posix.1-2001 marks .br ualarm () as obsolete. posix.1-2008 removes the specification of .br ualarm (). 4.3bsd, susv2, and posix do not define any errors. .sh notes posix.1-2001 does not specify what happens if the .i usecs argument is 0. .\" this case is not documented in hp-us, solar, freebsd, netbsd, or openbsd! on linux (and probably most other systems), the effect is to cancel any pending alarm. .pp the type .i useconds_t is an unsigned integer type capable of holding integers in the range [0,1000000]. on the original bsd implementation, and in glibc before version 2.1, the arguments to .br ualarm () were instead typed as .ir "unsigned int" . programs will be more portable if they never mention .i useconds_t explicitly. .pp the interaction of this function with other timer functions such as .br alarm (2), .br sleep (3), .br nanosleep (2), .br setitimer (2), .br timer_create (2), .br timer_delete (2), .br timer_getoverrun (2), .br timer_gettime (2), .br timer_settime (2), .br usleep (3) is unspecified. .pp this function is obsolete. use .br setitimer (2) or posix interval timers .rb ( timer_create (2), etc.) instead. .sh see also .br alarm (2), .br getitimer (2), .br nanosleep (2), .br select (2), .br setitimer (2), .br usleep (3), .br time (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 1993 rickard e. faith (faith@cs.unc.edu) .\" portions extracted from /usr/include/sys/socket.h, which does not have .\" any authorship information in it. it is probably available under the gpl. .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" .\" other portions are from the 6.9 (berkeley) 3/10/91 man page: .\" .\" copyright (c) 1983 the regents of the university of california. .\" all rights reserved. .\" .\" %%%license_start(bsd_4_clause_ucb) .\" redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. all advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" this product includes software developed by the university of .\" california, berkeley and its contributors. .\" 4. neither the name of the university nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" this software is provided by the regents and contributors ``as is'' and .\" any express or implied warranties, including, but not limited to, the .\" implied warranties of merchantability and fitness for a particular purpose .\" are disclaimed. in no event shall the regents or contributors be liable .\" for any direct, indirect, incidental, special, exemplary, or consequential .\" damages (including, but not limited to, procurement of substitute goods .\" or services; loss of use, data, or profits; or business interruption) .\" however caused and on any theory of liability, whether in contract, strict .\" liability, or tort (including negligence or otherwise) arising in any way .\" out of the use of this software, even if advised of the possibility of .\" such damage. .\" %%%license_end .\" .\" modified 1997-01-31 by eric s. raymond .\" modified 1998, 1999 by andi kleen .\" modified 2004-06-23 by michael kerrisk .\" .th connect 2 2021-03-22 "linux" "linux programmer's manual" .sh name connect \- initiate a connection on a socket .sh synopsis .nf .b #include .pp .bi "int connect(int " sockfd ", const struct sockaddr *" addr , .bi " socklen_t " addrlen ); .fi .sh description the .br connect () system call connects the socket referred to by the file descriptor .i sockfd to the address specified by .ir addr . the .i addrlen argument specifies the size of .ir addr . the format of the address in .i addr is determined by the address space of the socket .ir sockfd ; see .br socket (2) for further details. .pp if the socket .i sockfd is of type .br sock_dgram , then .i addr is the address to which datagrams are sent by default, and the only address from which datagrams are received. if the socket is of type .b sock_stream or .br sock_seqpacket , this call attempts to make a connection to the socket that is bound to the address specified by .ir addr . .pp some protocol sockets (e.g., unix domain stream sockets) may successfully .br connect () only once. .pp some protocol sockets (e.g., datagram sockets in the unix and internet domains) may use .br connect () multiple times to change their association. .pp some protocol sockets (e.g., tcp sockets as well as datagram sockets in the unix and internet domains) may dissolve the association by connecting to an address with the .i sa_family member of .i sockaddr set to .br af_unspec ; thereafter, the socket can be connected to another address. .rb ( af_unspec is supported on linux since kernel 2.2.) .sh return value if the connection or binding succeeds, zero is returned. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors the following are general socket errors only. there may be other domain-specific error codes. .tp .b eacces for unix domain sockets, which are identified by pathname: write permission is denied on the socket file, or search permission is denied for one of the directories in the path prefix. (see also .br path_resolution (7).) .tp .br eacces ", " eperm the user tried to connect to a broadcast address without having the socket broadcast flag enabled or the connection request failed because of a local firewall rule. .ip .b eacces can also be returned if an selinux policy denied a connection (for example, if there is a policy saying that an http proxy can only connect to ports associated with http servers, and the proxy tries to connect to a different port). dd .tp .b eaddrinuse local address is already in use. .tp .b eaddrnotavail (internet domain sockets) the socket referred to by .i sockfd had not previously been bound to an address and, upon attempting to bind it to an ephemeral port, it was determined that all port numbers in the ephemeral port range are currently in use. see the discussion of .i /proc/sys/net/ipv4/ip_local_port_range in .br ip (7). .tp .b eafnosupport the passed address didn't have the correct address family in its .i sa_family field. .tp .b eagain for nonblocking unix domain sockets, the socket is nonblocking, and the connection cannot be completed immediately. for other socket families, there are insufficient entries in the routing cache. .tp .b ealready the socket is nonblocking and a previous connection attempt has not yet been completed. .tp .b ebadf .i sockfd is not a valid open file descriptor. .tp .b econnrefused a .br connect () on a stream socket found no one listening on the remote address. .tp .b efault the socket structure address is outside the user's address space. .tp .b einprogress the socket is nonblocking and the connection cannot be completed immediately. (unix domain sockets failed with .br eagain instead.) it is possible to .br select (2) or .br poll (2) for completion by selecting the socket for writing. after .br select (2) indicates writability, use .br getsockopt (2) to read the .b so_error option at level .b sol_socket to determine whether .br connect () completed successfully .rb ( so_error is zero) or unsuccessfully .rb ( so_error is one of the usual error codes listed here, explaining the reason for the failure). .tp .b eintr the system call was interrupted by a signal that was caught; see .br signal (7). .\" for tcp, the connection will complete asynchronously. .\" see http://lkml.org/lkml/2005/7/12/254 .tp .b eisconn the socket is already connected. .tp .b enetunreach network is unreachable. .tp .b enotsock the file descriptor .i sockfd does not refer to a socket. .tp .b eprototype the socket type does not support the requested communications protocol. this error can occur, for example, on an attempt to connect a unix domain datagram socket to a stream socket. .tp .b etimedout timeout while attempting connection. the server may be too busy to accept new connections. note that for ip sockets the timeout may be very long when syncookies are enabled on the server. .sh conforming to posix.1-2001, posix.1-2008, svr4, 4.4bsd, .rb (connect () first appeared in 4.2bsd). .\" svr4 documents the additional .\" general error codes .\" .br eaddrnotavail , .\" .br einval , .\" .br eafnosupport , .\" .br ealready , .\" .br eintr , .\" .br eprototype , .\" and .\" .br enosr . .\" it also .\" documents many additional error conditions not described here. .sh notes for background on the .i socklen_t type, see .br accept (2). .pp if .br connect () fails, consider the state of the socket as unspecified. portable applications should close the socket and create a new one for reconnecting. .sh examples an example of the use of .br connect () is shown in .br getaddrinfo (3). .sh see also .br accept (2), .br bind (2), .br getsockname (2), .br listen (2), .br socket (2), .br path_resolution (7), .br selinux (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2008 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_equal 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_equal \- compare thread ids .sh synopsis .nf .b #include .pp .bi "int pthread_equal(pthread_t " t1 ", pthread_t " t2 ); .pp compile and link with \fi\-pthread\fp. .fi .sh description the .br pthread_equal () function compares two thread identifiers. .sh return value if the two thread ids are equal, .br pthread_equal () returns a nonzero value; otherwise, it returns 0. .sh errors this function always succeeds. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_equal () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes the .br pthread_equal () function is necessary because thread ids should be considered opaque: there is no portable way for applications to directly compare two .i pthread_t values. .sh see also .br pthread_create (3), .br pthread_self (3), .br pthreads (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2002 andries brouwer .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th tcgetsid 3 2021-03-22 "gnu" "linux programmer's manual" .sh name tcgetsid \- get session id .sh synopsis .nf .br "#define _xopen_source 500" " /* see feature_test_macros(7) */" .b "#include " .pp .bi "pid_t tcgetsid(int " fd ); .fi .sh description the function .br tcgetsid () returns the session id of the current session that has the terminal associated to .i fd as controlling terminal. this terminal must be the controlling terminal of the calling process. .sh return value when .i fd refers to the controlling terminal of our session, the function .br tcgetsid () will return the session id of this session. otherwise, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b ebadf .i fd is not a valid file descriptor. .tp .b enotty the calling process does not have a controlling terminal, or it has one but it is not described by .ir fd . .sh versions .br tcgetsid () is provided in glibc since version 2.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br tcgetsid () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes this function is implemented via the .b tiocgsid .br ioctl (2), present since linux 2.1.71. .sh see also .br getsid (2) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2021 by christian brauner .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th mount_setattr 2 2021-08-27 "linux" "linux programmer's manual" .sh name mount_setattr \- change properties of a mount or mount tree .sh synopsis .nf .pp .br "#include " " /* definition of " at_* " constants */" .br "#include " " /* definition of " mount_attr_* " constants */" .br "#include " " /* definition of " sys_* " constants */" .b #include .pp .bi "int syscall(sys_mount_setattr, int " dirfd ", const char *" pathname , .bi " unsigned int " flags ", struct mount_attr *" attr \ ", size_t " size ); .fi .pp .ir note : glibc provides no wrapper for .br mount_setattr (), necessitating the use of .br syscall (2). .sh description the .br mount_setattr () system call changes the mount properties of a mount or an entire mount tree. if .i pathname is a relative pathname, then it is interpreted relative to the directory referred to by the file descriptor .ir dirfd . if .i dirfd is the special value .br at_fdcwd , then .i pathname is interpreted relative to the current working directory of the calling process. if .i pathname is the empty string and .b at_empty_path is specified in .ir flags , then the mount properties of the mount identified by .i dirfd are changed. (see .br openat (2) for an explanation of why the .i dirfd argument is useful.) .pp the .br mount_setattr () system call uses an extensible structure .ri ( "struct mount_attr" ) to allow for future extensions. any non-flag extensions to .br mount_setattr () will be implemented as new fields appended to the this structure, with a zero value in a new field resulting in the kernel behaving as though that extension field was not present. therefore, the caller .i must zero-fill this structure on initialization. see the "extensibility" subsection under .b notes for more details. .pp the .i size argument should usually be specified as .ir "sizeof(struct mount_attr)" . however, if the caller is using a kernel that supports an extended .ir "struct mount_attr" , but the caller does not intend to make use of these features, it is possible to pass the size of an earlier version of the structure together with the extended structure. this allows the kernel to not copy later parts of the structure that aren't used anyway. with each extension that changes the size of .ir "struct mount_attr" , the kernel will expose a definition of the form .bi mount_attr_size_ver number\c \&. for example, the macro for the size of the initial version of .i struct mount_attr is .br mount_attr_size_ver0 . .pp the .i flags argument can be used to alter the pathname resolution behavior. the supported values are: .tp .b at_empty_path if .i pathname is the empty string, change the mount properties on .i dirfd itself. .tp .b at_recursive change the mount properties of the entire mount tree. .tp .b at_symlink_nofollow don't follow trailing symbolic links. .tp .b at_no_automount don't trigger automounts. .pp the .i attr argument of .br mount_setattr () is a structure of the following form: .pp .in +4n .ex struct mount_attr { __u64 attr_set; /* mount properties to set */ __u64 attr_clr; /* mount properties to clear */ __u64 propagation; /* mount propagation type */ __u64 userns_fd; /* user namespace file descriptor */ }; .ee .in .pp the .i attr_set and .i attr_clr members are used to specify the mount properties that are supposed to be set or cleared for a mount or mount tree. flags set in .i attr_set enable a property on a mount or mount tree, and flags set in .i attr_clr remove a property from a mount or mount tree. .pp when changing mount properties, the kernel will first clear the flags specified in the .i attr_clr field, and then set the flags specified in the .i attr_set field. for example, these settings: .pp .in +4n .ex struct mount_attr attr = { .attr_clr = mount_attr_noexec | mount_attr_nodev, .attr_set = mount_attr_rdonly | mount_attr_nosuid, }; .ee .in .pp are equivalent to the following steps: .pp .in +4n .ex unsigned int current_mnt_flags = mnt->mnt_flags; /* * clear all flags set in .attr_clr, * clearing mount_attr_noexec and mount_attr_nodev. */ current_mnt_flags &= ~attr->attr_clr; /* * now set all flags set in .attr_set, * applying mount_attr_rdonly and mount_attr_nosuid. */ current_mnt_flags |= attr->attr_set; mnt->mnt_flags = current_mnt_flags; .ee .in .pp as a result of this change, the mount or mount tree (a) is read-only; (b) blocks the execution of set-user-id and set-group-id programs; (c) allows execution of programs; and (d) allows access to devices. .pp multiple changes with the same set of flags requested in .i attr_clr and .i attr_set are guaranteed to be idempotent after the changes have been applied. .pp the following mount attributes can be specified in the .i attr_set or .i attr_clr fields: .tp .b mount_attr_rdonly if set in .ir attr_set , makes the mount read-only. if set in .ir attr_clr , removes the read-only setting if set on the mount. .tp .b mount_attr_nosuid if set in .ir attr_set , causes the mount not to honor the set-user-id and set-group-id mode bits and file capabilities when executing programs. if set in .ir attr_clr , clears the set-user-id, set-group-id, and file capability restriction if set on this mount. .tp .b mount_attr_nodev if set in .ir attr_set , prevents access to devices on this mount. if set in .ir attr_clr , removes the restriction that prevented accessing devices on this mount. .tp .b mount_attr_noexec if set in .ir attr_set , prevents executing programs on this mount. if set in .ir attr_clr , removes the restriction that prevented executing programs on this mount. .tp .b mount_attr_nosymfollow if set in .ir attr_set , prevents following symbolic links on this mount. if set in .ir attr_clr , removes the restriction that prevented following symbolic links on this mount. .tp .b mount_attr_nodiratime if set in .ir attr_set , prevents updating access time for directories on this mount. if set in .ir attr_clr , removes the restriction that prevented updating access time for directories. note that .b mount_attr_nodiratime can be combined with other access-time settings and is implied by the noatime setting. all other access-time settings are mutually exclusive. .tp .br mount_attr__atime " - changing access-time settings" the access-time values listed below are an enumeration that includes the value zero, expressed in the bits defined by the mask .br mount_attr__atime . even though these bits are an enumeration (in contrast to the other mount flags such as .br mount_attr_noexec ), they are nonetheless passed in .i attr_set and .i attr_clr for consistency with .br fsmount (2), which introduced this behavior. .ip note that, since the access-time values are an enumeration rather than bit values, a caller wanting to transition to a different access-time setting cannot simply specify the access-time setting in .ir attr_set , but must also include .b mount_attr__atime in the .i attr_clr field. the kernel will verify that .b mount_attr__atime isn't partially set in .ir attr_clr (i.e., either all bits in the .b mount_attr__atime bit field are either set or clear), and that .i attr_set doesn't have any access-time bits set if .b mount_attr__atime isn't set in .ir attr_clr . .rs .tp .b mount_attr_relatime when a file is accessed via this mount, update the file's last access time (atime) only if the current value of atime is less than or equal to the file's last modification time (mtime) or last status change time (ctime). .ip to enable this access-time setting on a mount or mount tree, .b mount_attr_relatime must be set in .i attr_set and .b mount_attr__atime must be set in the .i attr_clr field. .tp .b mount_attr_noatime do not update access times for (all types of) files on this mount. .ip to enable this access-time setting on a mount or mount tree, .b mount_attr_noatime must be set in .i attr_set and .b mount_attr__atime must be set in the .i attr_clr field. .tp .b mount_attr_strictatime always update the last access time (atime) when files are accessed on this mount. .ip to enable this access-time setting on a mount or mount tree, .b mount_attr_strictatime must be set in .i attr_set and .b mount_attr__atime must be set in the .i attr_clr field. .re .tp .b mount_attr_idmap if set in .ir attr_set , creates an id-mapped mount. the id mapping is taken from the user namespace specified in .i userns_fd and attached to the mount. .ip since it is not supported to change the id mapping of a mount after it has been id mapped, it is invalid to specify .b mount_attr_idmap in .ir attr_clr . .ip for further details, see the subsection "id-mapped mounts" under notes. .pp the .i propagation field is used to specify the propagation type of the mount or mount tree. this field either has the value zero, meaning leave the propagation type unchanged, or it has one of the following values: .tp .b ms_private turn all mounts into private mounts. .tp .b ms_shared turn all mounts into shared mounts. .tp .b ms_slave turn all mounts into dependent mounts. .tp .b ms_unbindable turn all mounts into unbindable mounts. .pp for further details on the above propagation types, see .br mount_namespaces (7). .sh return value on success, .br mount_setattr () returns zero. on error, \-1 is returned and .i errno is set to indicate the cause of the error. .sh errors .tp .b ebadf .i pathname is relative but .i dirfd is neither .b at_fdcwd nor a valid file descriptor. .tp .b ebadf .i userns_fd is not a valid file descriptor. .tp .b ebusy the caller tried to change the mount to .br mount_attr_rdonly , but the mount still holds files open for writing. .tp .b einval the pathname specified via the .i dirfd and .i pathname arguments to .br mount_setattr () isn't a mount point. .tp .b einval an unsupported value was set in .ir flags . .tp .b einval an unsupported value was specified in the .i attr_set field of .ir mount_attr . .tp .b einval an unsupported value was specified in the .i attr_clr field of .ir mount_attr . .tp .b einval an unsupported value was specified in the .i propagation field of .ir mount_attr . .tp .b einval more than one of .br ms_shared , .br ms_slave , .br ms_private , or .b ms_unbindable was set in the .i propagation field of .ir mount_attr . .tp .b einval an access-time setting was specified in the .i attr_set field without .b mount_attr__atime being set in the .i attr_clr field. .tp .b einval .b mount_attr_idmap was specified in .ir attr_clr . .tp .b einval a file descriptor value was specified in .i userns_fd which exceeds .br int_max . .tp .b einval a valid file descriptor value was specified in .ir userns_fd , but the file descriptor did not refer to a user namespace. .tp .b einval the underlying filesystem does not support id-mapped mounts. .tp .b einval the mount that is to be id mapped is not a detached mount; that is, the mount has not previously been visible in a mount namespace. .tp .b einval a partial access-time setting was specified in .i attr_clr instead of .b mount_attr__atime being set. .tp .b einval the mount is located outside the caller's mount namespace. .tp .b einval the underlying filesystem has been mounted in a mount namespace that is owned by a noninitial user namespace .tp .b enoent a pathname was empty or had a nonexistent component. .tp .b enomem when changing mount propagation to .br ms_shared , a new peer group id needs to be allocated for all mounts without a peer group id set. this allocation failed because there was not enough memory to allocate the relevant internal structures. .tp .b enospc when changing mount propagation to .br ms_shared , a new peer group id needs to be allocated for all mounts without a peer group id set. this allocation failed because the kernel has run out of ids. .\" christian bruner: i.e. someone has somehow managed to .\" allocate so many peer groups and managed to keep the kernel running .\" (???) that the ida has ran out of ids .\" note that technically further error codes are possible that are .\" specific to the id allocation implementation used. .tp .b eperm one of the mounts had at least one of .br mount_attr_noatime , .br mount_attr_nodev , .br mount_attr_nodiratime , .br mount_attr_noexec , .br mount_attr_nosuid , or .b mount_attr_rdonly set and the flag is locked. mount attributes become locked on a mount if: .rs .ip \(bu 3 a new mount or mount tree is created causing mount propagation across user namespaces (i.e., propagation to a mount namespace owned by a different user namespace). the kernel will lock the aforementioned flags to prevent these sensitive properties from being altered. .ip \(bu a new mount and user namespace pair is created. this happens for example when specifying .b clone_newuser | clone_newns in .br unshare (2), .br clone (2), or .br clone3 (2). the aforementioned flags become locked in the new mount namespace to prevent sensitive mount properties from being altered. since the newly created mount namespace will be owned by the newly created user namespace, a calling process that is privileged in the new user namespace would\(emin the absence of such locking\(embe able to alter sensitive mount properties (e.g., to remount a mount that was marked read-only as read-write in the new mount namespace). .re .tp .b eperm a valid file descriptor value was specified in .ir userns_fd , but the file descriptor refers to the initial user namespace. .tp .b eperm an attempt was made to add an id mapping to a mount that is already id mapped. .tp .b eperm the caller does not have .b cap_sys_admin in the initial user namespace. .sh versions .br mount_setattr () first appeared in linux 5.12. .\" commit 7d6beb71da3cc033649d641e1e608713b8220290 .\" commit 2a1867219c7b27f928e2545782b86daaf9ad50bd .\" commit 9caccd41541a6f7d6279928d9f971f6642c361af .sh conforming to .br mount_setattr () is linux-specific. .sh notes .ss id-mapped mounts creating an id-mapped mount makes it possible to change the ownership of all files located under a mount. thus, id-mapped mounts make it possible to change ownership in a temporary and localized way. it is a localized change because the ownership changes are visible only via a specific mount. all other users and locations where the filesystem is exposed are unaffected. it is a temporary change because the ownership changes are tied to the lifetime of the mount. .pp whenever callers interact with the filesystem through an id-mapped mount, the id mapping of the mount will be applied to user and group ids associated with filesystem objects. this encompasses the user and group ids associated with inodes and also the following .br xattr (7) keys: .ip \(bu 3 .ir security.capability , whenever filesystem capabilities are stored or returned in the .b vfs_cap_revision_3 format, which stores a root user id alongside the capabilities (see .br capabilities (7)). .ip \(bu .i system.posix_acl_access and .ir system.posix_acl_default , whenever user ids or group ids are stored in .b acl_user or .b acl_group entries. .pp the following conditions must be met in order to create an id-mapped mount: .ip \(bu 3 the caller must have the .b cap_sys_admin capability in the initial user namespace. .ip \(bu the filesystem must be mounted in a mount namespace that is owned by the initial user namespace. .ip \(bu the underlying filesystem must support id-mapped mounts. currently, the .br xfs (5), .br ext4 (5), and .b fat filesystems support id-mapped mounts with more filesystems being actively worked on. .ip \(bu the mount must not already be id-mapped. this also implies that the id mapping of a mount cannot be altered. .ip \(bu the mount must be a detached mount; that is, it must have been created by calling .br open_tree (2) with the .b open_tree_clone flag and it must not already have been visible in a mount namespace. (to put things another way: the mount must not have been attached to the filesystem hierarchy with a system call such as .br move_mount (2).) .pp id mappings can be created for user ids, group ids, and project ids. an id mapping is essentially a mapping of a range of user or group ids into another or the same range of user or group ids. id mappings are written to map files as three numbers separated by white space. the first two numbers specify the starting user or group id in each of the two user namespaces. the third number specifies the range of the id mapping. for example, a mapping for user ids such as "1000\ 1001\ 1" would indicate that user id 1000 in the caller's user namespace is mapped to user id 1001 in its ancestor user namespace. since the map range is 1, only user id 1000 is mapped. .pp it is possible to specify up to 340 id mappings for each id mapping type. if any user ids or group ids are not mapped, all files owned by that unmapped user or group id will appear as being owned by the overflow user id or overflow group id respectively. .pp further details on setting up id mappings can be found in .br user_namespaces (7). .pp in the common case, the user namespace passed in .i userns_fd (together with .b mount_attr_idmap in .ir attr_set ) to create an id-mapped mount will be the user namespace of a container. in other scenarios it will be a dedicated user namespace associated with a user's login session as is the case for portable home directories in .br systemd-homed.service (8)). it is also perfectly fine to create a dedicated user namespace for the sake of id mapping a mount. .pp id-mapped mounts can be useful in the following and a variety of other scenarios: .ip \(bu 3 sharing files or filesystems between multiple users or multiple machines, especially in complex scenarios. for example, id-mapped mounts are used to implement portable home directories in .br systemd-homed.service (8), where they allow users to move their home directory to an external storage device and use it on multiple computers where they are assigned different user ids and group ids. this effectively makes it possible to assign random user ids and group ids at login time. .ip \(bu sharing files or filesystems from the host with unprivileged containers. this allows a user to avoid having to change ownership permanently through .br chown (2). .ip \(bu id mapping a container's root filesystem. users don't need to change ownership permanently through .br chown (2). especially for large root filesystems, using .br chown (2) can be prohibitively expensive. .ip \(bu sharing files or filesystems between containers with non-overlapping id mappings. .ip \(bu implementing discretionary access (dac) permission checking for filesystems lacking a concept of ownership. .ip \(bu efficiently changing ownership on a per-mount basis. in contrast to .br chown (2), changing ownership of large sets of files is instantaneous with id-mapped mounts. this is especially useful when ownership of an entire root filesystem of a virtual machine or container is to be changed as mentioned above. with id-mapped mounts, a single .br mount_setattr () system call will be sufficient to change the ownership of all files. .ip \(bu taking the current ownership into account. id mappings specify precisely what a user or group id is supposed to be mapped to. this contrasts with the .br chown (2) system call which cannot by itself take the current ownership of the files it changes into account. it simply changes the ownership to the specified user id and group id. .ip \(bu locally and temporarily restricted ownership changes. id-mapped mounts make it possible to change ownership locally, restricting the ownership changes to specific mounts, and temporarily as the ownership changes only apply as long as the mount exists. by contrast, changing ownership via the .br chown (2) system call changes the ownership globally and permanently. .\" .ss extensibility in order to allow for future extensibility, .br mount_setattr () requires the user-space application to specify the size of the .i mount_attr structure that it is passing. by providing this information, it is possible for .br mount_setattr () to provide both forwards- and backwards-compatibility, with .i size acting as an implicit version number. (because new extension fields will always be appended, the structure size will always increase.) this extensibility design is very similar to other system calls such as .br perf_setattr (2), .br perf_event_open (2), .br clone3 (2) and .br openat2 (2). .pp let .i usize be the size of the structure as specified by the user-space application, and let .i ksize be the size of the structure which the kernel supports, then there are three cases to consider: .ip \(bu 3 if .i ksize equals .ir usize , then there is no version mismatch and .i attr can be used verbatim. .ip \(bu if .i ksize is larger than .ir usize , then there are some extension fields that the kernel supports which the user-space application is unaware of. because a zero value in any added extension field signifies a no-op, the kernel treats all of the extension fields not provided by the user-space application as having zero values. this provides backwards-compatibility. .ip \(bu if .i ksize is smaller than .ir usize , then there are some extension fields which the user-space application is aware of but which the kernel does not support. because any extension field must have its zero values signify a no-op, the kernel can safely ignore the unsupported extension fields if they are all zero. if any unsupported extension fields are non-zero, then \-1 is returned and .i errno is set to .br e2big . this provides forwards-compatibility. .pp because the definition of .i struct mount_attr may change in the future (with new fields being added when system headers are updated), user-space applications should zero-fill .i struct mount_attr to ensure that recompiling the program with new headers will not result in spurious errors at runtime. the simplest way is to use a designated initializer: .pp .in +4n .ex struct mount_attr attr = { .attr_set = mount_attr_rdonly, .attr_clr = mount_attr_nodev }; .ee .in .pp alternatively, the structure can be zero-filled using .br memset (3) or similar functions: .pp .in +4n .ex struct mount_attr attr; memset(&attr, 0, sizeof(attr)); attr.attr_set = mount_attr_rdonly; attr.attr_clr = mount_attr_nodev; .ee .in .pp a user-space application that wishes to determine which extensions the running kernel supports can do so by conducting a binary search on .i size with a structure which has every byte nonzero (to find the largest value which doesn't produce an error of .br e2big ). .sh examples .ex /* * this program allows the caller to create a new detached mount * and set various properties on it. */ #define _gnu_source #include #include #include #include #include #include #include #include #include #include #include static inline int mount_setattr(int dirfd, const char *pathname, unsigned int flags, struct mount_attr *attr, size_t size) { return syscall(sys_mount_setattr, dirfd, pathname, flags, attr, size); } static inline int open_tree(int dirfd, const char *filename, unsigned int flags) { return syscall(sys_open_tree, dirfd, filename, flags); } static inline int move_mount(int from_dirfd, const char *from_pathname, int to_dirfd, const char *to_pathname, unsigned int flags) { return syscall(sys_move_mount, from_dirfd, from_pathname, to_dirfd, to_pathname, flags); } static const struct option longopts[] = { {"map\-mount", required_argument, null, 'a'}, {"recursive", no_argument, null, 'b'}, {"read\-only", no_argument, null, 'c'}, {"block\-setid", no_argument, null, 'd'}, {"block\-devices", no_argument, null, 'e'}, {"block\-exec", no_argument, null, 'f'}, {"no\-access\-time", no_argument, null, 'g'}, { null, 0, null, 0 }, }; #define exit_log(format, ...) do \e { \e fprintf(stderr, format, ##__va_args__); \e exit(exit_failure); \e } while (0) int main(int argc, char *argv[]) { struct mount_attr *attr = &(struct mount_attr){}; int fd_userns = \-1; bool recursive = false; int index = 0; int ret; while ((ret = getopt_long_only(argc, argv, "", longopts, &index)) != \-1) { switch (ret) { case 'a': fd_userns = open(optarg, o_rdonly | o_cloexec); if (fd_userns == \-1) exit_log("%m \- failed top open %s\en", optarg); break; case 'b': recursive = true; break; case 'c': attr\->attr_set |= mount_attr_rdonly; break; case 'd': attr\->attr_set |= mount_attr_nosuid; break; case 'e': attr\->attr_set |= mount_attr_nodev; break; case 'f': attr\->attr_set |= mount_attr_noexec; break; case 'g': attr\->attr_set |= mount_attr_noatime; attr\->attr_clr |= mount_attr__atime; break; default: exit_log("invalid argument specified"); } } if ((argc \- optind) < 2) exit_log("missing source or target mount point\en"); const char *source = argv[optind]; const char *target = argv[optind + 1]; /* in the following, \-1 as the \(aqdirfd\(aq argument ensures that open_tree() fails if \(aqsource\(aq is not an absolute pathname. */ .\" christian brauner .\" when writing programs i like to never use relative paths with at_fdcwd .\" because. because making assumptions about the current working directory .\" of the calling process is just too easy to get wrong; especially when .\" pivot_root() or chroot() are in play. .\" my absolut preference (joke intended) is to open a well-known starting .\" point with an absolute path to get a dirfd and then scope all future .\" operations beneath that dirfd. this already works with old-style .\" openat() and _very_ cautious programming but openat2() and its .\" resolve-flag space have made this **chef's kiss**. .\" if i can't operate based on a well-known dirfd i use absolute paths .\" with a -ebadf dirfd passed to *at() functions. int fd_tree = open_tree(\-1, source, open_tree_clone | open_tree_cloexec | at_empty_path | (recursive ? at_recursive : 0)); if (fd_tree == \-1) exit_log("%m \- failed to open %s\en", source); if (fd_userns >= 0) { attr\->attr_set |= mount_attr_idmap; attr\->userns_fd = fd_userns; } ret = mount_setattr(fd_tree, "", at_empty_path | (recursive ? at_recursive : 0), attr, sizeof(struct mount_attr)); if (ret == \-1) exit_log("%m \- failed to change mount attributes\en"); close(fd_userns); /* in the following, \-1 as the \(aqto_dirfd\(aq argument ensures that open_tree() fails if \(aqtarget\(aq is not an absolute pathname. */ ret = move_mount(fd_tree, "", \-1, target, move_mount_f_empty_path); if (ret == \-1) exit_log("%m \- failed to attach mount to %s\en", target); close(fd_tree); exit(exit_success); } .ee .sh see also .br newgidmap (1), .br newuidmap (1), .br clone (2), .br mount (2), .br unshare (2), .br proc (5), .br capabilities (7), .br mount_namespaces (7), .br user_namespaces (7), .br xattr (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man7/iso_8859-7.7 .so man2/setpgid.2 .so man3/getttyent.3 .\" copyright (c) 2009 linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th pthread_kill 3 2021-03-22 "linux" "linux programmer's manual" .sh name pthread_kill \- send a signal to a thread .sh synopsis .nf .b #include .pp .bi "int pthread_kill(pthread_t " thread ", int " sig ); .fi .pp compile and link with \fi\-pthread\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br pthread_kill (): .nf _posix_c_source >= 199506l || _xopen_source >= 500 .fi .sh description the .br pthread_kill () function sends the signal .i sig to .ir thread , a thread in the same process as the caller. the signal is asynchronously directed to .ir thread . .pp if .i sig is 0, then no signal is sent, but error checking is still performed. .sh return value on success, .br pthread_kill () returns 0; on error, it returns an error number, and no signal is sent. .sh errors .tp .b einval an invalid signal was specified. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br pthread_kill () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes signal dispositions are process-wide: if a signal handler is installed, the handler will be invoked in the thread .ir thread , but if the disposition of the signal is "stop", "continue", or "terminate", this action will affect the whole process. .pp the glibc implementation of .br pthread_kill () gives an error .rb ( einval ) on attempts to send either of the real-time signals used internally by the nptl threading implementation. see .br nptl (7) for details. .pp posix.1-2008 recommends that if an implementation detects the use of a thread id after the end of its lifetime, .br pthread_kill () should return the error .br esrch . the glibc implementation returns this error in the cases where an invalid thread id can be detected. but note also that posix says that an attempt to use a thread id whose lifetime has ended produces undefined behavior, and an attempt to use an invalid thread id in a call to .br pthread_kill () can, for example, cause a segmentation fault. .sh see also .br kill (2), .br sigaction (2), .br sigpending (2), .br pthread_self (3), .br pthread_sigmask (3), .br raise (3), .br pthreads (7), .br signal (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/unimplemented.2 .so man3/isalpha.3 .so man3/pthread_getattr_default_np.3 .so man3/mtrace.3 .so man7/system_data_types.7 .so man3/gethostbyname.3 .so man3/mq_timedsend.3 .\" because mq_timedsend(3) is layered on a system call of the same name .so man3/stailq.3 .so man3/memchr.3 .so man3/strspn.3 .\" (c) copyright 1992-1999 rickard e. faith and david a. wheeler .\" (faith@cs.unc.edu and dwheeler@ida.org) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified sun jul 25 11:06:05 1993 by rik faith (faith@cs.unc.edu) .\" modified sat jun 8 00:39:52 1996 by aeb .\" modified wed jun 16 23:00:00 1999 by david a. wheeler (dwheeler@ida.org) .\" modified thu jul 15 12:43:28 1999 by aeb .\" modified sun jan 6 18:26:25 2002 by martin schulze .\" modified tue jul 27 20:12:02 2004 by colin watson .\" 2007-05-30, mtk: various rewrites and moved much text to new man-pages.7. .\" .th man 7 2021-03-22 "linux" "linux programmer's manual" .sh name man \- macros to format man pages .sh synopsis .b groff \-tascii \-man .i file \&... .br .b groff \-tps \-man .i file \&... .pp .b man .ri [ section ] .i title .sh description this manual page explains the .b "groff an.tmac" macro package (often called the .b man macro package). this macro package should be used by developers when writing or porting man pages for linux. it is fairly compatible with other versions of this macro package, so porting man pages should not be a major problem (exceptions include the net-2 bsd release, which uses a totally different macro package called mdoc; see .br mdoc (7)). .pp note that net-2 bsd mdoc man pages can be used with .b groff simply by specifying the .b \-mdoc option instead of the .b \-man option. using the .b \-mandoc option is, however, recommended, since this will automatically detect which macro package is in use. .pp for conventions that should be employed when writing man pages for the linux \fiman-pages\fp package, see .br man\-pages (7). .ss title line the first command in a man page (after comment lines, that is, lines that start with \fb.\e"\fp) should be .pp .rs .b \&.th .i "title section date source manual" .re .pp for details of the arguments that should be supplied to the .b th command, see .br man\-pages (7). .pp note that bsd mdoc-formatted pages begin with the .b dd command, not the .b th command. .ss sections sections are started with .b \&.sh followed by the heading name. .\" the following doesn't seem to be required (see debian bug 411303), .\" if the name contains spaces and appears .\" on the same line as .\" .br \&.sh , .\" then place the heading in double quotes. .pp the only mandatory heading is name, which should be the first section and be followed on the next line by a one-line description of the program: .pp .rs \&.sh name .br item \e- description .re .pp it is extremely important that this format is followed, and that there is a backslash before the single dash which follows the item name. this syntax is used by the .br mandb (8) program to create a database of short descriptions for the .br whatis (1) and .br apropos (1) commands. (see .br lexgrog (1) for further details on the syntax of the name section.) .pp for a list of other sections that might appear in a manual page, see .br man\-pages (7). .ss fonts the commands to select the type face are: .tp 4 .b \&.b bold .tp .b \&.bi bold alternating with italics (especially useful for function specifications) .tp .b \&.br bold alternating with roman (especially useful for referring to other manual pages) .tp .b \&.i italics .tp .b \&.ib italics alternating with bold .tp .b \&.ir italics alternating with roman .tp .b \&.rb roman alternating with bold .tp .b \&.ri roman alternating with italics .tp .b \&.sb small alternating with bold .tp .b \&.sm small (useful for acronyms) .pp traditionally, each command can have up to six arguments, but the gnu implementation removes this limitation (you might still want to limit yourself to 6 arguments for portability's sake). arguments are delimited by spaces. double quotes can be used to specify an argument which contains spaces. for the macros that produce alternating type faces, the arguments will be printed next to each other without intervening spaces, so that the .b \&.br command can be used to specify a word in bold followed by a mark of punctuation in roman. if no arguments are given, the command is applied to the following line of text. .ss other macros and strings below are other relevant macros and predefined strings. unless noted otherwise, all macros cause a break (end the current line of text). many of these macros set or use the "prevailing indent". the "prevailing indent" value is set by any macro with the parameter .i i below; macros may omit .i i in which case the current prevailing indent will be used. as a result, successive indented paragraphs can use the same indent without respecifying the indent value. a normal (nonindented) paragraph resets the prevailing indent value to its default value (0.5 inches). by default, a given indent is measured in ens; try to use ens or ems as units for indents, since these will automatically adjust to font size changes. the other key macro definitions are: .ss normal paragraphs .tp 9m .b \&.lp same as .b \&.pp (begin a new paragraph). .tp .b \&.p same as .b \&.pp (begin a new paragraph). .tp .b \&.pp begin a new paragraph and reset prevailing indent. .ss relative margin indent .tp 9m .bi \&.rs " i" start relative margin indent: moves the left margin .i i to the right (if .i i is omitted, the prevailing indent value is used). a new prevailing indent is set to 0.5 inches. as a result, all following paragraph(s) will be indented until the corresponding .br \&.re . .tp .b \&.re end relative margin indent and restores the previous value of the prevailing indent. .ss indented paragraph macros .tp 9m .bi \&.hp " i" begin paragraph with a hanging indent (the first line of the paragraph is at the left margin of normal paragraphs, and the rest of the paragraph's lines are indented). .tp .bi \&.ip " x i" indented paragraph with optional hanging tag. if the tag .i x is omitted, the entire following paragraph is indented by .ir i . if the tag .i x is provided, it is hung at the left margin before the following indented paragraph (this is just like .b \&.tp except the tag is included with the command instead of being on the following line). if the tag is too long, the text after the tag will be moved down to the next line (text will not be lost or garbled). for bulleted lists, use this macro with \e(bu (bullet) or \e(em (em dash) as the tag, and for numbered lists, use the number or letter followed by a period as the tag; this simplifies translation to other formats. .tp .bi \&.tp " i" begin paragraph with hanging tag. the tag is given on the next line, but its results are like those of the .b \&.ip command. .ss hypertext link macros .tp .bi \&.ur " url" insert a hypertext link to the uri (url) .ir url , with all text up to the following .b \&.ue macro as the link text. .tp .b \&.ue \c .ri [ trailer ] terminate the link text of the preceding .b \&.ur macro, with the optional .i trailer (if present, usually a closing parenthesis and/or end-of-sentence punctuation) immediately following. for non-html output devices (e.g., .br "man \-tutf8" ), the link text is followed by the url in angle brackets; if there is no link text, the url is printed as its own link text, surrounded by angle brackets. (angle brackets may not be available on all output devices.) for the html output device, the link text is hyperlinked to the url; if there is no link text, the url is printed as its own link text. .pp these macros have been supported since gnu troff 1.20 (2009-01-05) and heirloom doctools troff since 160217 (2016-02-17). .ss miscellaneous macros .tp 9m .b \&.dt reset tabs to default tab values (every 0.5 inches); does not cause a break. .tp .bi \&.pd " d" set inter-paragraph vertical distance to d (if omitted, d=0.4v); does not cause a break. .tp .bi \&.ss " t" subheading .i t (like .br \&.sh , but used for a subsection inside a section). .ss predefined strings the .b man package has the following predefined strings: .ip \e*r registration symbol: \*r .ip \e*s change to default font size .ip \e*(tm trademark symbol: \*(tm .ip \e*(lq left angled double quote: \*(lq .ip \e*(rq right angled double quote: \*(rq .ss safe subset although technically .b man is a troff macro package, in reality a large number of other tools process man page files that don't implement all of troff's abilities. thus, it's best to avoid some of troff's more exotic abilities where possible to permit these other tools to work correctly. avoid using the various troff preprocessors (if you must, go ahead and use .br tbl (1), but try to use the .b ip and .b tp commands instead for two-column tables). avoid using computations; most other tools can't process them. use simple commands that are easy to translate to other formats. the following troff macros are believed to be safe (though in many cases they will be ignored by translators): .br \e" , .br . , .br ad , .br bp , .br br , .br ce , .br de , .br ds , .br el , .br ie , .br if , .br fi , .br ft , .br hy , .br ig , .br in , .br na , .br ne , .br nf , .br nh , .br ps , .br so , .br sp , .br ti , .br tr . .pp you may also use many troff escape sequences (those sequences beginning with \e). when you need to include the backslash character as normal text, use \ee. other sequences you may use, where x or xx are any characters and n is any digit, include: .br \e\(aq , .br \e\(ga , .br \e- , .br \e. , .br \e" , .br \e% , .br \e*x , .br \e*(xx , .br \e(xx , .br \e$n , .br \enx , .br \en(xx , .br \efx , and .br \ef(xx . avoid using the escape sequences for drawing graphics. .pp do not use the optional parameter for .b bp (break page). use only positive values for .b sp (vertical space). don't define a macro .rb ( de ) with the same name as a macro in this or the mdoc macro package with a different meaning; it's likely that such redefinitions will be ignored. every positive indent .rb ( in ) should be paired with a matching negative indent (although you should be using the .b rs and .b re macros instead). the condition test .rb ( if,ie ) should only have \(aqt\(aq or \(aqn\(aq as the condition. only translations .rb ( tr ) that can be ignored should be used. font changes .rb ( ft and the \fb\ef\fp escape sequence) should only have the values 1, 2, 3, 4, r, i, b, p, or cw (the ft command may also have no parameters). .pp if you use capabilities beyond these, check the results carefully on several tools. once you've confirmed that the additional capability is safe, let the maintainer of this document know about the safe command or sequence that should be added to this list. .sh files .ir /usr/share/groff/ [*/] tmac/an.tmac .br .i /usr/man/whatis .sh notes by all means include full urls (or uris) in the text itself; some tools such as .br man2html (1) can automatically turn them into hypertext links. you can also use the .b ur and .b ue macros to identify links to related information. if you include urls, use the full url (e.g., .ur http://www.kernel.org .ue ) to ensure that tools can automatically find the urls. .pp tools processing these files should open the file and examine the first nonwhitespace character. a period (.) or single quote (\(aq) at the beginning of a line indicates a troff-based file (such as man or mdoc). a left angle bracket (<) indicates an sgml/xml-based file (such as html or docbook). anything else suggests simple ascii text (e.g., a "catman" result). .pp many man pages begin with \fb\(aq\e"\fp followed by a space and a list of characters, indicating how the page is to be preprocessed. for portability's sake to non-troff translators we recommend that you avoid using anything other than .br tbl (1), and linux can detect that automatically. however, you might want to include this information so your man page can be handled by other (less capable) systems. here are the definitions of the preprocessors invoked by these characters: .tp 3 .b e eqn(1) .tp .b g grap(1) .tp .b p pic(1) .tp .b r refer(1) .tp .b t tbl(1) .tp .b v vgrind(1) .sh bugs most of the macros describe formatting (e.g., font type and spacing) instead of marking semantic content (e.g., this text is a reference to another page), compared to formats like mdoc and docbook (even html has more semantic markings). this situation makes it harder to vary the .b man format for different media, to make the formatting consistent for a given media, and to automatically insert cross-references. by sticking to the safe subset described above, it should be easier to automate transitioning to a different reference page format in the future. .pp the sun macro .b tx is not implemented. .\" .sh authors .\" .ip \(em 3m .\" james clark (jjc@jclark.com) wrote the implementation of the macro package. .\" .ip \(em .\" rickard e. faith (faith@cs.unc.edu) wrote the initial version of .\" this manual page. .\" .ip \(em .\" jens schweikhardt (schweikh@noc.fdn.de) wrote the linux man-page mini-howto .\" (which influenced this manual page). .\" .ip \(em .\" david a. wheeler (dwheeler@ida.org) heavily modified this .\" manual page, such as adding detailed information on sections and macros. .sh see also .br apropos (1), .br groff (1), .br lexgrog (1), .br man (1), .br man2html (1), .br whatis (1), .br groff_man (7), .br groff_www (7), .br man\-pages (7), .br mdoc (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 2002 walter harms (walter.harms@informatik.uni-oldenburg.de) .\" .\" %%%license_start(gpl_noversion_oneline) .\" distributed under gpl .\" %%%license_end .\" .\" based on the description in glibc source and infopages .\" .\" corrections and additions, aeb .th envz_add 3 2021-03-22 "" "linux programmer's manual" .sh name envz_add, envz_entry, envz_get, envz_merge, envz_remove, envz_strip \- environment string support .sh synopsis .nf .b "#include " .pp .bi "error_t envz_add(char **restrict " envz ", size_t *restrict " envz_len , .bi " const char *restrict " name \ ", const char *restrict " value ); .pp .bi "char *envz_entry(const char *restrict " envz ", size_t " envz_len , .bi " const char *restrict " name ); .pp .bi "char *envz_get(const char *restrict " envz ", size_t " envz_len , .bi " const char *restrict " name ); .pp .bi "error_t envz_merge(char **restrict " envz ", size_t *restrict " envz_len , .bi " const char *restrict " envz2 ", size_t " envz2_len , .bi " int " override ); .pp .bi "void envz_remove(char **restrict " envz ", size_t *restrict " envz_len , .bi " const char *restrict " name ); .pp .bi "void envz_strip(char **restrict " envz ", size_t *restrict " envz_len ); .fi .sh description these functions are glibc-specific. .pp an argz vector is a pointer to a character buffer together with a length, see .br argz_add (3). an envz vector is a special argz vector, namely one where the strings have the form "name=value". everything after the first \(aq=\(aq is considered to be the value. if there is no \(aq=\(aq, the value is taken to be null. (while the value in case of a trailing \(aq=\(aq is the empty string "".) .pp these functions are for handling envz vectors. .pp .br envz_add () adds the string .ri \&" name = value \&" (in case .i value is non-null) or .ri \&" name \&" (in case .i value is null) to the envz vector .ri ( *envz ,\ *envz_len ) and updates .i *envz and .ir *envz_len . if an entry with the same .i name existed, it is removed. .pp .br envz_entry () looks for .i name in the envz vector .ri ( envz ,\ envz_len ) and returns the entry if found, or null if not. .pp .br envz_get () looks for .i name in the envz vector .ri ( envz ,\ envz_len ) and returns the value if found, or null if not. (note that the value can also be null, namely when there is an entry for .i name without \(aq=\(aq sign.) .pp .br envz_merge () adds each entry in .i envz2 to .ir *envz , as if with .br envz_add (). if .i override is true, then values in .i envz2 will supersede those with the same name in .ir *envz , otherwise not. .pp .br envz_remove () removes the entry for .i name from .ri ( *envz ,\ *envz_len ) if there was one. .pp .br envz_strip () removes all entries with value null. .sh return value all envz functions that do memory allocation have a return type of .ir error_t (an integer type), and return 0 for success, and .b enomem if an allocation error occurs. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br envz_add (), .br envz_entry (), .br envz_get (), .br envz_merge (), .br envz_remove (), .br envz_strip () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to these functions are a gnu extension. .sh examples .ex #include #include #include int main(int argc, char *argv[], char *envp[]) { int e_len = 0; char *str; for (int i = 0; envp[i] != null; i++) e_len += strlen(envp[i]) + 1; str = envz_entry(*envp, e_len, "home"); printf("%s\en", str); str = envz_get(*envp, e_len, "home"); printf("%s\en", str); exit(exit_success); } .ee .sh see also .br argz_add (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2007 by michael kerrisk .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" 2007-07-31, mtk, created .\" .th timeradd 3 2021-03-22 "linux" "linux programmer's manual" .sh name timeradd, timersub, timercmp, timerclear, timerisset \- timeval operations .sh synopsis .nf .b #include .pp .bi "void timeradd(struct timeval *" a ", struct timeval *" b , .bi " struct timeval *" res ); .bi "void timersub(struct timeval *" a ", struct timeval *" b , .bi " struct timeval *" res ); .pp .bi "void timerclear(struct timeval *" tvp ); .bi "int timerisset(struct timeval *" tvp ); .pp .bi "int timercmp(struct timeval *" a ", struct timeval *" b ", " cmp ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp all functions shown above: .nf since glibc 2.19: _default_source glibc 2.19 and earlier: _bsd_source .fi .sh description the macros are provided to operate on .i timeval structures, defined in .i as: .pp .in +4n .ex struct timeval { time_t tv_sec; /* seconds */ suseconds_t tv_usec; /* microseconds */ }; .ee .in .pp .br timeradd () adds the time values in .i a and .ir b , and places the sum in the .i timeval pointed to by .ir res . the result is normalized such that .i res\->tv_usec has a value in the range 0 to 999,999. .pp .br timersub () subtracts the time value in .i b from the time value in .ir a , and places the result in the .i timeval pointed to by .ir res . the result is normalized such that .i res\->tv_usec has a value in the range 0 to 999,999. .pp .br timerclear () zeros out the .i timeval structure pointed to by .ir tvp , so that it represents the epoch: 1970-01-01 00:00:00 +0000 (utc). .pp .br timerisset () returns true (nonzero) if either field of the .i timeval structure pointed to by .i tvp contains a nonzero value. .pp .br timercmp () compares the timer values in .i a and .i b using the comparison operator .ir cmp , and returns true (nonzero) or false (0) depending on the result of the comparison. some systems (but not linux/glibc), have a broken .br timercmp () implementation, .\" hp-ux, tru64, irix have a definition like: .\"#define timercmp(tvp, uvp, cmp) \ .\" ((tvp)->tv_sec cmp (uvp)->tv_sec || \ .\" (tvp)->tv_sec == (uvp)->tv_sec && (tvp)->tv_usec cmp (uvp)->tv_usec) in which .i cmp of .ir >= , .ir <= , and .i == do not work; portable applications can instead use .pp !timercmp(..., <) !timercmp(..., >) !timercmp(..., !=) .sh return value .br timerisset () and .br timercmp () return true (nonzero) or false (0). .sh errors no errors are defined. .sh conforming to not in posix.1. present on most bsd derivatives. .sh see also .br gettimeofday (2), .br time (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 1995 jim van zandt .\" and copyright 2008, linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified 2002-07-27 walter harms .\" (walter.harms@informatik.uni-oldenburg.de) .\" .th expm1 3 2021-03-22 "" "linux programmer's manual" .sh name expm1, expm1f, expm1l \- exponential minus 1 .sh synopsis .nf .b #include .pp .bi "double expm1(double " x ); .bi "float expm1f(float " x ); .bi "long double expm1l(long double " x ); .pp .fi link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br expm1 (): .nf _isoc99_source || _posix_c_source >= 200112l || _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .pp .br expm1f (), .br expm1l (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description these functions return a value equivalent to .pp .nf exp(x) \- 1 .fi .pp the result is computed in a way that is accurate even if the value of .i x is near zero\(ema case where .i "exp(x) \- 1" would be inaccurate due to subtraction of two numbers that are nearly equal. .sh return value on success, these functions return .ir "exp(x)\ \-\ 1" . .pp if .i x is a nan, a nan is returned. .pp if .i x is +0 (\-0), +0 (\-0) is returned. .pp if .i x is positive infinity, positive infinity is returned. .pp if .i x is negative infinity, \-1 is returned. .pp if the result overflows, a range error occurs, and the functions return .rb \- huge_val , .rb \- huge_valf , or .rb \- huge_vall , respectively. .sh errors see .br math_error (7) for information on how to determine whether an error has occurred when calling these functions. .pp the following errors can occur: .tp range error, overflow .i errno is set to .br erange (but see bugs). an overflow floating-point exception .rb ( fe_overflow ) is raised. .\" .\" posix.1 specifies an optional range error (underflow) if .\" x is subnormal. glibc does not implement this. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br expm1 (), .br expm1f (), .br expm1l () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to c99, posix.1-2001, posix.1-2008. .\" bsd. .sh bugs before glibc 2.17, .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778 on certain architectures (e.g., x86, but not x86_64) .br expm1 () raised a bogus underflow floating-point exception for some large negative .i x values (where the function result approaches \-1). .pp before approximately glibc version 2.11, .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814 .\" e.g., expm1(1e5) through expm1(1.00199970127e5), .\" but not expm1(1.00199970128e5) and beyond. .br expm1 () raised a bogus invalid floating-point exception in addition to the expected overflow exception, and returned a nan instead of positive infinity, for some large positive .i x values. .pp before version 2.11, .\" it looks like the fix was in 2.11, or possibly 2.12. .\" i have no test system for 2.11, but 2.12 passes. .\" from the source (sysdeps/i386/fpu/s_expm1.s) it looks .\" like the changes were in 2.11. the glibc implementation did not set .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788 .i errno to .b erange when a range error occurred. .sh see also .br exp (3), .br log (3), .br log1p (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/mkstemp.3 .so man3/lrint.3 .so man3/expm1.3 .so man3/rpc.3 .\" copyright 2002 walter harms (walter.harms@informatik.uni-oldenburg.de) .\" and copyright 2008, linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(gpl_noversion_oneline) .\" distributed under gpl .\" %%%license_end .\" .\" based on glibc infopages .\" .th lgamma 3 2021-03-22 "" "linux programmer's manual" .sh name lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam \- log gamma function .sh synopsis .nf .b #include .pp .bi "double lgamma(double " x ); .bi "float lgammaf(float " x ); .bi "long double lgammal(long double " x ); .pp .bi "double lgamma_r(double " x ", int *" signp ); .bi "float lgammaf_r(float " x ", int *" signp ); .bi "long double lgammal_r(long double " x ", int *" signp ); .pp .bi "extern int " signgam ; .fi .pp link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .nf .br lgamma (): _isoc99_source || _posix_c_source >= 200112l || _xopen_source || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .pp .br lgammaf (), .br lgammal (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .pp .br lgamma_r (), .br lgammaf_r (), .br lgammal_r (): .nf /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .pp .ir signgam : .nf _xopen_source || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description for the definition of the gamma function, see .br tgamma (3). .pp the .br lgamma (), .br lgammaf (), and .br lgammal () functions return the natural logarithm of the absolute value of the gamma function. the sign of the gamma function is returned in the external integer .i signgam declared in .ir . it is 1 when the gamma function is positive or zero, \-1 when it is negative. .pp since using a constant location .i signgam is not thread-safe, the functions .br lgamma_r (), .br lgammaf_r (), and .br lgammal_r () have been introduced; they return the sign via the argument .ir signp . .sh return value on success, these functions return the natural logarithm of gamma(x). .pp if .i x is a nan, a nan is returned. .pp if .i x is 1 or 2, +0 is returned. .pp if .i x is positive infinity or negative infinity, positive infinity is returned. .pp if .i x is a nonpositive integer, a pole error occurs, and the functions return .rb + huge_val , .rb + huge_valf , or .rb + huge_vall , respectively. .pp if the result overflows, a range error occurs, .\" e.g., lgamma(dbl_max) and the functions return .br huge_val , .br huge_valf , or .br huge_vall , respectively, with the correct mathematical sign. .sh errors see .br math_error (7) for information on how to determine whether an error has occurred when calling these functions. .pp the following errors can occur: .tp pole error: \fix\fp is a nonpositive integer .i errno is set to .br erange (but see bugs). a divide-by-zero floating-point exception .rb ( fe_divbyzero ) is raised. .tp range error: result overflow .i errno is set to .br erange . an overflow floating-point exception .rb ( fe_overflow ) is raised. .\" glibc (as at 2.8) also supports an inexact .\" exception for various cases. .sh conforming to the .br lgamma () functions are specified in c99, posix.1-2001, and posix.1-2008. .i signgam is specified in posix.1-2001 and posix.1-2008, but not in c99. the .br lgamma_r () functions are nonstandard, but present on several other systems. .sh bugs in glibc 2.9 and earlier, .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6777 when a pole error occurs, .i errno is set to .br edom ; instead of the posix-mandated .br erange . since version 2.10, glibc does the right thing. .sh see also .br tgamma (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" this manpage is copyright (c) 2006 silicon graphics, inc. .\" christoph lameter .\" .\" %%%license_start(verbatim_two_para) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" %%%license_end .\" .\" fixme should programs normally be using move_pages() directly, or should .\" they rather be using interfaces in the numactl package? .\" (e.g., compare with recommendation in mbind(2)). .\" does this page need to give advice on this topic? .\" .th move_pages 2 2021-03-22 "linux" "linux programmer's manual" .sh name move_pages \- move individual pages of a process to another node .sh synopsis .nf .b #include .pp .bi "long move_pages(int " pid ", unsigned long " count ", void **" pages , .bi " const int *" nodes ", int *" status ", int " flags ); .fi .pp link with \fi\-lnuma\fp. .pp .ir note : there is no glibc wrapper for this system call; see notes. .sh description .br move_pages () moves the specified .i pages of the process .i pid to the memory nodes specified by .ir nodes . the result of the move is reflected in .ir status . the .i flags indicate constraints on the pages to be moved. .pp .i pid is the id of the process in which pages are to be moved. if .i pid is 0, then .br move_pages () moves pages of the calling process. .pp to move pages in another process requires the following privileges: .ip * 3 in kernels up to and including linux 4.12: the caller must be privileged .rb ( cap_sys_nice ) or the real or effective user id of the calling process must match the real or saved-set user id of the target process. .ip * the older rules allowed the caller to discover various virtual address choices made by the kernel that could lead to the defeat of address-space-layout randomization for a process owned by the same uid as the caller, the rules were changed starting with linux 4.13. since linux 4.13, .\" commit 197e7e521384a23b9e585178f3f11c9fa08274b9 permission is governed by a ptrace access mode .b ptrace_mode_read_realcreds check with respect to the target process; see .br ptrace (2). .pp .i count is the number of pages to move. it defines the size of the three arrays .ir pages , .ir nodes , and .ir status . .pp .i pages is an array of pointers to the pages that should be moved. these are pointers that should be aligned to page boundaries. .\" fixme describe the result if pointers in the 'pages' array are .\" not aligned to page boundaries addresses are specified as seen by the process specified by .ir pid . .pp .i nodes is an array of integers that specify the desired location for each page. each element in the array is a node number. .i nodes can also be null, in which case .br move_pages () does not move any pages but instead will return the node where each page currently resides, in the .i status array. obtaining the status of each page may be necessary to determine pages that need to be moved. .pp .i status is an array of integers that return the status of each page. the array contains valid values only if .br move_pages () did not return an error. preinitialization of the array to a value which cannot represent a real numa node or valid error of status array could help to identify pages that have been migrated. .pp .i flags specify what types of pages to move. .b mpol_mf_move means that only pages that are in exclusive use by the process are to be moved. .b mpol_mf_move_all means that pages shared between multiple processes can also be moved. the process must be privileged .rb ( cap_sys_nice ) to use .br mpol_mf_move_all . .ss page states in the status array the following values can be returned in each element of the .i status array. .tp .b 0..max_numnodes identifies the node on which the page resides. .tp .b \-eacces the page is mapped by multiple processes and can be moved only if .b mpol_mf_move_all is specified. .tp .b \-ebusy the page is currently busy and cannot be moved. try again later. this occurs if a page is undergoing i/o or another kernel subsystem is holding a reference to the page. .tp .b \-efault this is a zero page or the memory area is not mapped by the process. .tp .b \-eio unable to write back a page. the page has to be written back in order to move it since the page is dirty and the filesystem does not provide a migration function that would allow the move of dirty pages. .tp .b \-einval a dirty page cannot be moved. the filesystem does not provide a migration function and has no ability to write back pages. .tp .b \-enoent the page is not present. .tp .b \-enomem unable to allocate memory on target node. .sh return value on success .br move_pages () returns zero. .\" fixme . is the following quite true: does the wrapper in numactl .\" do the right thing? on error, it returns \-1, and sets .i errno to indicate the error. if positive value is returned, it is the number of nonmigrated pages. .sh errors .tp .b positive value the number of nonmigrated pages if they were the result of nonfatal reasons (since .\" commit a49bd4d7163707de377aee062f17befef6da891b linux 4.17). .tp .b e2big too many pages to move. since linux 2.6.29, .\" commit 3140a2273009c01c27d316f35ab76a37e105fdd8 the kernel no longer generates this error. .tp .b eacces .\" fixme clarify "current cpuset" in the description of the eacces error. .\" is that the cpuset of the caller or the target? one of the target nodes is not allowed by the current cpuset. .tp .b efault parameter array could not be accessed. .tp .b einval flags other than .b mpol_mf_move and .b mpol_mf_move_all was specified or an attempt was made to migrate pages of a kernel thread. .tp .b enodev one of the target nodes is not online. .tp .b eperm the caller specified .b mpol_mf_move_all without sufficient privileges .rb ( cap_sys_nice ). or, the caller attempted to move pages of a process belonging to another user but did not have privilege to do so .rb ( cap_sys_nice ). .tp .b esrch process does not exist. .sh versions .br move_pages () first appeared on linux in version 2.6.18. .sh conforming to this system call is linux-specific. .sh notes glibc does not provide a wrapper for this system call. for information on library support, see .br numa (7). .pp use .br get_mempolicy (2) with the .b mpol_f_mems_allowed flag to obtain the set of nodes that are allowed by .\" fixme clarify "current cpuset". is that the cpuset of the caller .\" or the target? the current cpuset. note that this information is subject to change at any time by manual or automatic reconfiguration of the cpuset. .pp use of this function may result in pages whose location (node) violates the memory policy established for the specified addresses (see .br mbind (2)) and/or the specified process (see .br set_mempolicy (2)). that is, memory policy does not constrain the destination nodes used by .br move_pages (). .pp the .i header is not included with glibc, but requires installing .i libnuma\-devel or a similar package. .sh see also .br get_mempolicy (2), .br mbind (2), .br set_mempolicy (2), .br numa (3), .br numa_maps (5), .br cpuset (7), .br numa (7), .br migratepages (8), .br numastat (8) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man2/unimplemented.2 .\" copyright (c) 2002 andries brouwer .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" this replaces an earlier man page written by walter harms .\" . .\" .\" corrected return types; from fabian; 2004-10-05 .\" .th ecvt_r 3 2021-03-22 "gnu" "linux programmer's manual" .sh name ecvt_r, fcvt_r, qecvt_r, qfcvt_r \- convert a floating-point number to a string .sh synopsis .nf .b #include .pp .bi "int ecvt_r(double " number ", int " ndigits ", int *restrict " decpt , .bi " int *restrict " sign ", char *restrict " buf ", size_t " len ); .bi "int fcvt_r(double " number ", int " ndigits ", int *restrict " decpt , .bi " int *restrict " sign ", char *restrict " buf ", size_t " len ); .pp .bi "int qecvt_r(long double " number ", int " ndigits \ ", int *restrict " decpt , .bi " int *restrict " sign ", char *restrict " buf ", size_t " len ); .bi "int qfcvt_r(long double " number ", int " ndigits \ ", int *restrict " decpt , .bi " int *restrict " sign ", char *restrict " buf ", size_t " len ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br ecvt_r (), .br fcvt_r (), .br qecvt_r (), .br qfcvt_r (): .nf /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _svid_source || _bsd_source .fi .sh description the functions .br ecvt_r (), .br fcvt_r (), .br qecvt_r (), and .br qfcvt_r () are identical to .br ecvt (3), .br fcvt (3), .br qecvt (3), and .br qfcvt (3), respectively, except that they do not return their result in a static buffer, but instead use the supplied .i buf of size .ir len . see .br ecvt (3) and .br qecvt (3). .sh return value these functions return 0 on success, and \-1 otherwise. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br ecvt_r (), .br fcvt_r (), .br qecvt_r (), .br qfcvt_r () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to these functions are gnu extensions. .sh notes these functions are obsolete. instead, .br sprintf (3) is recommended. .sh see also .br ecvt (3), .br qecvt (3), .br sprintf (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/rpc.3 .\" copyright (c) 2013, peter schiffer (pschiffe@redhat.com) .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .th mtrace 1 2021-03-22 "gnu" "linux user manual" .sh name mtrace \- interpret the malloc trace log .sh synopsis .nf .br mtrace " [\fioption\fr]... [\fibinary\fr] \fimtracedata\fr" .fi .sh description .b mtrace is a perl script used to interpret and provide human readable output of the trace log contained in the file .ir mtracedata , whose contents were produced by .br mtrace (3). if .i binary is provided, the output of .b mtrace also contains the source file name with line number information for problem locations (assuming that .i binary was compiled with debugging information). .pp for more information about the .br mtrace (3) function and .b mtrace script usage, see .br mtrace (3). .sh options .tp .bi \fb\-\-help print help and exit. .tp .bi \fb\-\-version print version information and exit. .sh bugs for bug reporting instructions, please see: .ur http://www.gnu.org/software/libc/bugs.html .ue . .sh see also .br memusage (1), .br mtrace (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/qecvt.3 .so man3/tailq.3 .so man3/cacosh.3 .\" copyright (c) 2014 michael kerrisk .\" and copyright (c) 2014 david herrmann .\" .\" %%%license_start(gplv2+) .\" .\" this program is free software; you can redistribute it and/or modify .\" it under the terms of the gnu general public license as published by .\" the free software foundation; either version 2 of the license, or .\" (at your option) any later version. .\" .\" this program is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .th memfd_create 2 2021-03-22 linux "linux programmer's manual" .sh name memfd_create \- create an anonymous file .sh synopsis .nf .br "#define _gnu_source" " /* see feature_test_macros(7) */" .b #include .pp .bi "int memfd_create(const char *" name ", unsigned int " flags ");" .fi .sh description .br memfd_create () creates an anonymous file and returns a file descriptor that refers to it. the file behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on. however, unlike a regular file, it lives in ram and has a volatile backing storage. once all references to the file are dropped, it is automatically released. anonymous memory is used for all backing pages of the file. therefore, files created by .br memfd_create () have the same semantics as other anonymous .\" david herrmann: .\" memfd uses vm_noreserve so each page is accounted on first access. .\" this means, the overcommit-limits (see __vm_enough_memory()) and the .\" memory-cgroup limits (mem_cgroup_try_charge()) are applied. note that .\" those are accounted on "current" and "current->mm", that is, the .\" process doing the first page access. memory allocations such as those allocated using .br mmap (2) with the .br map_anonymous flag. .pp the initial size of the file is set to 0. following the call, the file size should be set using .br ftruncate (2). (alternatively, the file may be populated by calls to .br write (2) or similar.) .pp the name supplied in .i name is used as a filename and will be displayed as the target of the corresponding symbolic link in the directory .ir /proc/self/fd/ . the displayed name is always prefixed with .ir memfd: and serves only for debugging purposes. names do not affect the behavior of the file descriptor, and as such multiple files can have the same name without any side effects. .pp the following values may be bitwise ored in .ir flags to change the behavior of .br memfd_create (): .tp .br mfd_cloexec set the close-on-exec .rb ( fd_cloexec ) flag on the new file descriptor. see the description of the .b o_cloexec flag in .br open (2) for reasons why this may be useful. .tp .br mfd_allow_sealing allow sealing operations on this file. see the discussion of the .b f_add_seals and .br f_get_seals operations in .br fcntl (2), and also notes, below. the initial set of seals is empty. if this flag is not set, the initial set of seals will be .br f_seal_seal , meaning that no other seals can be set on the file. .\" fixme why is the mfd_allow_sealing behavior not simply the default? .\" is it worth adding some text explaining this? .tp .br mfd_hugetlb " (since linux 4.14)" .\" commit 749df87bd7bee5a79cef073f5d032ddb2b211de8 the anonymous file will be created in the hugetlbfs filesystem using huge pages. see the linux kernel source file .i documentation/admin\-guide/mm/hugetlbpage.rst for more information about hugetlbfs. .\" commit 47b9012ecdc747f6936395265e677d41e11a31ff specifying both .b mfd_hugetlb and .b mfd_allow_sealing in .i flags is supported since linux 4.16. .tp .br mfd_huge_2mb ", " mfd_huge_1gb ", " "..." used in conjunction with .b mfd_hugetlb to select alternative hugetlb page sizes (respectively, 2\ mb, 1\ gb, ...) on systems that support multiple hugetlb page sizes. definitions for known huge page sizes are included in the header file .i . .ip for details on encoding huge page sizes not included in the header file, see the discussion of the similarly named constants in .br mmap (2). .pp unused bits in .i flags must be 0. .pp as its return value, .br memfd_create () returns a new file descriptor that can be used to refer to the file. this file descriptor is opened for both reading and writing .rb ( o_rdwr ) and .b o_largefile is set for the file descriptor. .pp with respect to .br fork (2) and .br execve (2), the usual semantics apply for the file descriptor created by .br memfd_create (). a copy of the file descriptor is inherited by the child produced by .br fork (2) and refers to the same file. the file descriptor is preserved across .br execve (2), unless the close-on-exec flag has been set. .sh return value on success, .br memfd_create () returns a new file descriptor. on error, \-1 is returned and .i errno is set to indicate the error. .sh errors .tp .b efault the address in .ir name points to invalid memory. .tp .b einval .i flags included unknown bits. .tp .b einval .i name was too long. (the limit is .\" name_max - strlen("memfd:") 249 bytes, excluding the terminating null byte.) .tp .b einval both .b mfd_hugetlb and .b mfd_allow_sealing were specified in .ir flags . .tp .b emfile the per-process limit on the number of open file descriptors has been reached. .tp .b enfile the system-wide limit on the total number of open files has been reached. .tp .b enomem there was insufficient memory to create a new anonymous file. .sh versions the .br memfd_create () system call first appeared in linux 3.17; glibc support was added in version 2.27. .tp .b eperm the .b mfd_hugetlb flag was specified, but the caller was not privileged (did not have the .b cap_ipc_lock capability) and is not a member of the .i sysctl_hugetlb_shm_group group; see the description of .i /proc/sys/vm/sysctl_hugetlb_shm_group in .br proc (5). .sh conforming to the .br memfd_create () system call is linux-specific. .sh notes .\" see also http://lwn.net/articles/593918/ .\" and http://lwn.net/articles/594919/ and http://lwn.net/articles/591108/ the .br memfd_create () system call provides a simple alternative to manually mounting a .br tmpfs (5) filesystem and creating and opening a file in that filesystem. the primary purpose of .br memfd_create () is to create files and associated file descriptors that are used with the file-sealing apis provided by .br fcntl (2). .pp the .br memfd_create () system call also has uses without file sealing (which is why file-sealing is disabled, unless explicitly requested with the .br mfd_allow_sealing flag). in particular, it can be used as an alternative to creating files in .ir tmp or as an alternative to using the .br open (2) .b o_tmpfile in cases where there is no intention to actually link the resulting file into the filesystem. .ss file sealing in the absence of file sealing, processes that communicate via shared memory must either trust each other, or take measures to deal with the possibility that an untrusted peer may manipulate the shared memory region in problematic ways. for example, an untrusted peer might modify the contents of the shared memory at any time, or shrink the shared memory region. the former possibility leaves the local process vulnerable to time-of-check-to-time-of-use race conditions (typically dealt with by copying data from the shared memory region before checking and using it). the latter possibility leaves the local process vulnerable to .br sigbus signals when an attempt is made to access a now-nonexistent location in the shared memory region. (dealing with this possibility necessitates the use of a handler for the .br sigbus signal.) .pp dealing with untrusted peers imposes extra complexity on code that employs shared memory. memory sealing enables that extra complexity to be eliminated, by allowing a process to operate secure in the knowledge that its peer can't modify the shared memory in an undesired fashion. .pp an example of the usage of the sealing mechanism is as follows: .ip 1. 3 the first process creates a .br tmpfs (5) file using .br memfd_create (). the call yields a file descriptor used in subsequent steps. .ip 2. the first process sizes the file created in the previous step using .br ftruncate (2), maps it using .br mmap (2), and populates the shared memory with the desired data. .ip 3. the first process uses the .br fcntl (2) .b f_add_seals operation to place one or more seals on the file, in order to restrict further modifications on the file. (if placing the seal .br f_seal_write , then it will be necessary to first unmap the shared writable mapping created in the previous step. otherwise, behavior similar to .br f_seal_write can be achieved by using .br f_seal_future_write , which will prevent future writes via .br mmap (2) and .br write (2) from succeeding while keeping existing shared writable mappings). .ip 4. a second process obtains a file descriptor for the .br tmpfs (5) file and maps it. among the possible ways in which this could happen are the following: .rs .ip * 3 the process that called .br memfd_create () could transfer the resulting file descriptor to the second process via a unix domain socket (see .br unix (7) and .br cmsg (3)). the second process then maps the file using .br mmap (2). .ip * the second process is created via .br fork (2) and thus automatically inherits the file descriptor and mapping. (note that in this case and the next, there is a natural trust relationship between the two processes, since they are running under the same user id. therefore, file sealing would not normally be necessary.) .ip * the second process opens the file .ir /proc//fd/ , where .i is the pid of the first process (the one that called .br memfd_create ()), and .i is the number of the file descriptor returned by the call to .br memfd_create () in that process. the second process then maps the file using .br mmap (2). .re .ip 5. the second process uses the .br fcntl (2) .b f_get_seals operation to retrieve the bit mask of seals that has been applied to the file. this bit mask can be inspected in order to determine what kinds of restrictions have been placed on file modifications. if desired, the second process can apply further seals to impose additional restrictions (so long as the .br f_seal_seal seal has not yet been applied). .sh examples below are shown two example programs that demonstrate the use of .br memfd_create () and the file sealing api. .pp the first program, .ir t_memfd_create.c , creates a .br tmpfs (5) file using .br memfd_create (), sets a size for the file, maps it into memory, and optionally places some seals on the file. the program accepts up to three command-line arguments, of which the first two are required. the first argument is the name to associate with the file, the second argument is the size to be set for the file, and the optional third argument is a string of characters that specify seals to be set on file. .pp the second program, .ir t_get_seals.c , can be used to open an existing file that was created via .br memfd_create () and inspect the set of seals that have been applied to that file. .pp the following shell session demonstrates the use of these programs. first we create a .br tmpfs (5) file and set some seals on it: .pp .in +4n .ex $ \fb./t_memfd_create my_memfd_file 4096 sw &\fp [1] 11775 pid: 11775; fd: 3; /proc/11775/fd/3 .ee .in .pp at this point, the .i t_memfd_create program continues to run in the background. from another program, we can obtain a file descriptor for the file created by .br memfd_create () by opening the .ir /proc/[pid]/fd file that corresponds to the file descriptor opened by .br memfd_create (). using that pathname, we inspect the content of the .ir /proc/[pid]/fd symbolic link, and use our .i t_get_seals program to view the seals that have been placed on the file: .pp .in +4n .ex $ \fbreadlink /proc/11775/fd/3\fp /memfd:my_memfd_file (deleted) $ \fb./t_get_seals /proc/11775/fd/3\fp existing seals: write shrink .ee .in .ss program source: t_memfd_create.c \& .ex #define _gnu_source #include #include #include #include #include #include #include #define errexit(msg) do { perror(msg); exit(exit_failure); \e } while (0) int main(int argc, char *argv[]) { int fd; unsigned int seals; char *addr; char *name, *seals_arg; ssize_t len; if (argc < 3) { fprintf(stderr, "%s name size [seals]\en", argv[0]); fprintf(stderr, "\et\(aqseals\(aq can contain any of the " "following characters:\en"); fprintf(stderr, "\et\etg \- f_seal_grow\en"); fprintf(stderr, "\et\ets \- f_seal_shrink\en"); fprintf(stderr, "\et\etw \- f_seal_write\en"); fprintf(stderr, "\et\etw \- f_seal_future_write\en"); fprintf(stderr, "\et\ets \- f_seal_seal\en"); exit(exit_failure); } name = argv[1]; len = atoi(argv[2]); seals_arg = argv[3]; /* create an anonymous file in tmpfs; allow seals to be placed on the file. */ fd = memfd_create(name, mfd_allow_sealing); if (fd == \-1) errexit("memfd_create"); /* size the file as specified on the command line. */ if (ftruncate(fd, len) == \-1) errexit("truncate"); printf("pid: %jd; fd: %d; /proc/%jd/fd/%d\en", (intmax_t) getpid(), fd, (intmax_t) getpid(), fd); /* code to map the file and populate the mapping with data omitted. */ /* if a \(aqseals\(aq command\-line argument was supplied, set some seals on the file. */ if (seals_arg != null) { seals = 0; if (strchr(seals_arg, \(aqg\(aq) != null) seals |= f_seal_grow; if (strchr(seals_arg, \(aqs\(aq) != null) seals |= f_seal_shrink; if (strchr(seals_arg, \(aqw\(aq) != null) seals |= f_seal_write; if (strchr(seals_arg, \(aqw\(aq) != null) seals |= f_seal_future_write; if (strchr(seals_arg, \(aqs\(aq) != null) seals |= f_seal_seal; if (fcntl(fd, f_add_seals, seals) == \-1) errexit("fcntl"); } /* keep running, so that the file created by memfd_create() continues to exist. */ pause(); exit(exit_success); } .ee .ss program source: t_get_seals.c \& .ex #define _gnu_source #include #include #include #include #include #include #define errexit(msg) do { perror(msg); exit(exit_failure); \e } while (0) int main(int argc, char *argv[]) { int fd; unsigned int seals; if (argc != 2) { fprintf(stderr, "%s /proc/pid/fd/fd\en", argv[0]); exit(exit_failure); } fd = open(argv[1], o_rdwr); if (fd == \-1) errexit("open"); seals = fcntl(fd, f_get_seals); if (seals == \-1) errexit("fcntl"); printf("existing seals:"); if (seals & f_seal_seal) printf(" seal"); if (seals & f_seal_grow) printf(" grow"); if (seals & f_seal_write) printf(" write"); if (seals & f_seal_future_write) printf(" future_write"); if (seals & f_seal_shrink) printf(" shrink"); printf("\en"); /* code to map the file and access the contents of the resulting mapping omitted. */ exit(exit_success); } .ee .sh see also .br fcntl (2), .br ftruncate (2), .br mmap (2), .br shmget (2), .br shm_open (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright (c) 2010, michael kerrisk .\" .\" %%%license_start(gplv2+_doc_full) .\" this is free documentation; you can redistribute it and/or .\" modify it under the terms of the gnu general public license as .\" published by the free software foundation; either version 2 of .\" the license, or (at your option) any later version. .\" .\" the gnu general public license's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" this manual is distributed in the hope that it will be useful, .\" but without any warranty; without even the implied warranty of .\" merchantability or fitness for a particular purpose. see the .\" gnu general public license for more details. .\" .\" you should have received a copy of the gnu general public .\" license along with this manual; if not, see .\" . .\" %%%license_end .\" .th lio_listio 3 2021-03-22 "" "linux programmer's manual" .sh name lio_listio \- initiate a list of i/o requests .sh synopsis .nf .b "#include " .pp .bi "int lio_listio(int " mode ", struct aiocb *restrict const " aiocb_list [restrict], .bi " int " nitems ", struct sigevent *restrict " sevp ); .pp link with \fi\-lrt\fp. .fi .sh description the .br lio_listio () function initiates the list of i/o operations described by the array .ir aiocb_list . .pp the .i mode operation has one of the following values: .tp .b lio_wait the call blocks until all operations are complete. the .i sevp argument is ignored. .tp .b lio_nowait the i/o operations are queued for processing and the call returns immediately. when all of the i/o operations complete, asynchronous notification occurs, as specified by the .ir sevp argument; see .br sigevent (7) for details. if .ir sevp is null, no asynchronous notification occurs. .pp the .i aiocb_list argument is an array of pointers to .i aiocb structures that describe i/o operations. these operations are executed in an unspecified order. the .i nitems argument specifies the size of the array .ir aiocb_list . null pointers in .i aiocb_list are ignored. .pp in each control block in .ir aiocb_list , the .i aio_lio_opcode field specifies the i/o operation to be initiated, as follows: .tp .br lio_read initiate a read operation. the operation is queued as for a call to .br aio_read (3) specifying this control block. .tp .br lio_write initiate a write operation. the operation is queued as for a call to .br aio_write (3) specifying this control block. .tp .br lio_nop ignore this control block. .pp the remaining fields in each control block have the same meanings as for .br aio_read (3) and .br aio_write (3). the .i aio_sigevent fields of each control block can be used to specify notifications for the individual i/o operations (see .br sigevent (7)). .sh return value if .i mode is .br lio_nowait , .br lio_listio () returns 0 if all i/o operations are successfully queued. otherwise, \-1 is returned, and .i errno is set to indicate the error. .pp if .i mode is .br lio_wait , .br lio_listio () returns 0 when all of the i/o operations have completed successfully. otherwise, \-1 is returned, and .i errno is set to indicate the error. .pp the return status from .br lio_listio () provides information only about the call itself, not about the individual i/o operations. one or more of the i/o operations may fail, but this does not prevent other operations completing. the status of individual i/o operations in .ir aiocb_list can be determined using .br aio_error (3). when an operation has completed, its return status can be obtained using .br aio_return (3). individual i/o operations can fail for the reasons described in .br aio_read (3) and .br aio_write (3). .sh errors the .br lio_listio () function may fail for the following reasons: .tp .b eagain out of resources. .tp .b eagain .\" doesn't happen in glibc(?) the number of i/o operations specified by .i nitems would cause the limit .br aio_max to be exceeded. .tp .b eintr .i mode was .br lio_wait and a signal was caught before all i/o operations completed; see .br signal (7). (this may even be one of the signals used for asynchronous i/o completion notification.) .tp .b einval .i mode is invalid, or .\" doesn't happen in glibc(?) .i nitems exceeds the limit .br aio_listio_max . .tp .b eio one of more of the operations specified by .ir aiocb_list failed. .\" e.g., ioa_reqprio or aio_lio_opcode was invalid the application can check the status of each operation using .br aio_return (3). .pp if .br lio_listio () fails with the error .br eagain , .br eintr , or .br eio , then some of the operations in .ir aiocb_list may have been initiated. if .br lio_listio () fails for any other reason, then none of the i/o operations has been initiated. .sh versions the .br lio_listio () function is available since glibc 2.1. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br lio_listio () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008. .sh notes it is a good idea to zero out the control blocks before use. the control blocks must not be changed while the i/o operations are in progress. the buffer areas being read into or written from .\" or the control block of the operation must not be accessed during the operations or undefined results may occur. the memory areas involved must remain valid. .pp simultaneous i/o operations specifying the same .i aiocb structure produce undefined results. .sh see also .br aio_cancel (3), .br aio_error (3), .br aio_fsync (3), .br aio_return (3), .br aio_suspend (3), .br aio_write (3), .br aio (7) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/y0.3 .so man3/strchr.3 .\" copyright (c) 1998 andries brouwer (aeb@cwi.nl) .\" and copyright (c) 2002, 2006, 2008, 2012, 2013, 2015 michael kerrisk .\" and copyright guillem jover .\" and copyright (c) 2010 andi kleen .\" and copyright (c) 2012 cyrill gorcunov .\" and copyright (c) 2014 dave hansen / intel .\" and copyright (c) 2016 eugene syromyatnikov .\" and copyright (c) 2018 konrad rzeszutek wilk .\" and copyright (c) 2020 dave martin .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" modified thu nov 11 04:19:42 met 1999, aeb: added pr_get_pdeathsig .\" modified 27 jun 02, michael kerrisk .\" added pr_set_dumpable, pr_get_dumpable, .\" pr_set_keepcaps, pr_get_keepcaps .\" modified 2006-08-30 guillem jover .\" updated linux versions where the options where introduced. .\" added pr_set_timing, pr_get_timing, pr_set_name, pr_get_name, .\" pr_set_unalign, pr_get_unalign, pr_set_fpemu, pr_get_fpemu, .\" pr_set_fpexc, pr_get_fpexc .\" 2008-04-29 serge hallyn, document pr_capbset_read and pr_capbset_drop .\" 2008-06-13 erik bosman, .\" document pr_get_tsc and pr_set_tsc. .\" 2008-06-15 mtk, document pr_set_seccomp, pr_get_seccomp .\" 2009-10-03 andi kleen, document pr_mce_kill .\" 2012-04 cyrill gorcunov, document pr_set_mm .\" 2012-04-25 michael kerrisk, document pr_task_perf_events_disable and .\" pr_task_perf_events_enable .\" 2012-09-20 kees cook, update pr_set_seccomp for mode 2 .\" 2012-09-20 kees cook, document pr_set_no_new_privs, pr_get_no_new_privs .\" 2012-10-25 michael kerrisk, document pr_set_timerslack and .\" pr_get_timerslack .\" 2013-01-10 kees cook, document pr_set_ptracer .\" 2012-02-04 michael kerrisk, document pr_{set,get}_child_subreaper .\" 2014-11-10 dave hansen, document pr_mpx_{en,dis}able_management .\" .\" .th prctl 2 2021-03-22 "linux" "linux programmer's manual" .sh name prctl \- operations on a process or thread .sh synopsis .nf .b #include .pp .bi "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 , .bi " unsigned long " arg4 ", unsigned long " arg5 ); .fi .sh description .br prctl () manipulates various aspects of the behavior of the calling thread or process. .pp note that careless use of some .br prctl () operations can confuse the user-space run-time environment, so these operations should be used with care. .pp .br prctl () is called with a first argument describing what to do (with values defined in \fi\fp), and further arguments with a significance depending on the first one. the first argument can be: .\" .\" prctl pr_cap_ambient .tp .br pr_cap_ambient " (since linux 4.3)" .\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08 reads or changes the ambient capability set of the calling thread, according to the value of .ir arg2 , which must be one of the following: .rs .\" .tp .b pr_cap_ambient_raise the capability specified in .i arg3 is added to the ambient set. the specified capability must already be present in both the permitted and the inheritable sets of the process. this operation is not permitted if the .b secbit_no_cap_ambient_raise securebit is set. .tp .b pr_cap_ambient_lower the capability specified in .i arg3 is removed from the ambient set. .tp .b pr_cap_ambient_is_set the .br prctl () call returns 1 if the capability in .i arg3 is in the ambient set and 0 if it is not. .tp .br pr_cap_ambient_clear_all all capabilities will be removed from the ambient set. this operation requires setting .i arg3 to zero. .re .ip in all of the above operations, .i arg4 and .i arg5 must be specified as 0. .ip higher-level interfaces layered on top of the above operations are provided in the .br libcap (3) library in the form of .br cap_get_ambient (3), .br cap_set_ambient (3), and .br cap_reset_ambient (3). .\" prctl pr_capbset_read .tp .br pr_capbset_read " (since linux 2.6.25)" return (as the function result) 1 if the capability specified in .i arg2 is in the calling thread's capability bounding set, or 0 if it is not. (the capability constants are defined in .ir .) the capability bounding set dictates whether the process can receive the capability through a file's permitted capability set on a subsequent call to .br execve (2). .ip if the capability specified in .i arg2 is not valid, then the call fails with the error .br einval . .ip a higher-level interface layered on top of this operation is provided in the .br libcap (3) library in the form of .br cap_get_bound (3). .\" prctl pr_capbset_drop .tp .br pr_capbset_drop " (since linux 2.6.25)" if the calling thread has the .b cap_setpcap capability within its user namespace, then drop the capability specified by .i arg2 from the calling thread's capability bounding set. any children of the calling thread will inherit the newly reduced bounding set. .ip the call fails with the error: .b eperm if the calling thread does not have the .br cap_setpcap ; .br einval if .i arg2 does not represent a valid capability; or .br einval if file capabilities are not enabled in the kernel, in which case bounding sets are not supported. .ip a higher-level interface layered on top of this operation is provided in the .br libcap (3) library in the form of .br cap_drop_bound (3). .\" prctl pr_set_child_subreaper .tp .br pr_set_child_subreaper " (since linux 3.4)" .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b if .i arg2 is nonzero, set the "child subreaper" attribute of the calling process; if .i arg2 is zero, unset the attribute. .ip a subreaper fulfills the role of .br init (1) for its descendant processes. when a process becomes orphaned (i.e., its immediate parent terminates), then that process will be reparented to the nearest still living ancestor subreaper. subsequently, calls to .br getppid (2) in the orphaned process will now return the pid of the subreaper process, and when the orphan terminates, it is the subreaper process that will receive a .br sigchld signal and will be able to .br wait (2) on the process to discover its termination status. .ip the setting of the "child subreaper" attribute is not inherited by children created by .br fork (2) and .br clone (2). the setting is preserved across .br execve (2). .ip establishing a subreaper process is useful in session management frameworks where a hierarchical group of processes is managed by a subreaper process that needs to be informed when one of the processes\(emfor example, a double-forked daemon\(emterminates (perhaps so that it can restart that process). some .br init (1) frameworks (e.g., .br systemd (1)) employ a subreaper process for similar reasons. .\" prctl pr_get_child_subreaper .tp .br pr_get_child_subreaper " (since linux 3.4)" return the "child subreaper" setting of the caller, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_dumpable .tp .br pr_set_dumpable " (since linux 2.3.20)" set the state of the "dumpable" attribute, which determines whether core dumps are produced for the calling process upon delivery of a signal whose default behavior is to produce a core dump. .ip in kernels up to and including 2.6.12, .i arg2 must be either 0 .rb ( suid_dump_disable , process is not dumpable) or 1 .rb ( suid_dump_user , process is dumpable). between kernels 2.6.13 and 2.6.17, .\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502 the value 2 was also permitted, which caused any binary which normally would not be dumped to be dumped readable by root only; for security reasons, this feature has been removed. .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2 .\" subject: fix prctl privilege escalation (cve-2006-2451) .\" from: marcel holtmann .\" date: 2006-07-12 11:12:00 (see also the description of .i /proc/sys/fs/\:suid_dumpable in .br proc (5).) .ip normally, the "dumpable" attribute is set to 1. however, it is reset to the current value contained in the file .ir /proc/sys/fs/\:suid_dumpable (which by default has the value 0), in the following circumstances: .\" see kernel/cred.c::commit_creds() (linux 3.18 sources) .rs .ip * 3 the process's effective user or group id is changed. .ip * the process's filesystem user or group id is changed (see .br credentials (7)). .ip * the process executes .rb ( execve (2)) a set-user-id or set-group-id program, resulting in a change of either the effective user id or the effective group id. .ip * the process executes .rb ( execve (2)) a program that has file capabilities (see .br capabilities (7)), .\" see kernel/cred.c::commit_creds() but only if the permitted capabilities gained exceed those already permitted for the process. .\" also certain namespace operations; .re .ip processes that are not dumpable can not be attached via .br ptrace (2) .br ptrace_attach ; see .br ptrace (2) for further details. .ip if a process is not dumpable, the ownership of files in the process's .ir /proc/[pid] directory is affected as described in .br proc (5). .\" prctl pr_get_dumpable .tp .br pr_get_dumpable " (since linux 2.3.20)" return (as the function result) the current state of the calling process's dumpable attribute. .\" since linux 2.6.13, the dumpable flag can have the value 2, .\" but in 2.6.13 pr_get_dumpable simply returns 1 if the dumpable .\" flags has a nonzero value. this was fixed in 2.6.14. .\" prctl pr_set_endian .tp .br pr_set_endian " (since linux 2.6.18, powerpc only)" set the endian-ness of the calling process to the value given in \fiarg2\fp, which should be one of the following: .\" respectively 0, 1, 2 .br pr_endian_big , .br pr_endian_little , or .b pr_endian_ppc_little (powerpc pseudo little endian). .\" prctl pr_get_endian .tp .br pr_get_endian " (since linux 2.6.18, powerpc only)" return the endian-ness of the calling process, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_fp_mode .tp .br pr_set_fp_mode " (since linux 4.0, only on mips)" .\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8 on the mips architecture, user-space code can be built using an abi which permits linking with code that has more restrictive floating-point (fp) requirements. for example, user-space code may be built to target the o32 fpxx abi and linked with code built for either one of the more restrictive fp32 or fp64 abis. when more restrictive code is linked in, the overall requirement for the process is to use the more restrictive floating-point mode. .ip because the kernel has no means of knowing in advance which mode the process should be executed in, and because these restrictions can change over the lifetime of the process, the .b pr_set_fp_mode operation is provided to allow control of the floating-point mode from user space. .ip .\" https://dmz-portal.mips.com/wiki/mips_o32_abi_-_fr0_and_fr1_interlinking the .i (unsigned int) arg2 argument is a bit mask describing the floating-point mode used: .rs .tp .br pr_fp_mode_fr when this bit is .i unset (so called .br fr=0 " or " fr0 mode), the 32 floating-point registers are 32 bits wide, and 64-bit registers are represented as a pair of registers (even- and odd- numbered, with the even-numbered register containing the lower 32 bits, and the odd-numbered register containing the higher 32 bits). .ip when this bit is .i set (on supported hardware), the 32 floating-point registers are 64 bits wide (so called .br fr=1 " or " fr1 mode). note that modern mips implementations (mips r6 and newer) support .b fr=1 mode only. .ip applications that use the o32 fp32 abi can operate only when this bit is .i unset .rb ( fr=0 ; or they can be used with fre enabled, see below). applications that use the o32 fp64 abi (and the o32 fp64a abi, which exists to provide the ability to operate with existing fp32 code; see below) can operate only when this bit is .i set .rb ( fr=1 ). applications that use the o32 fpxx abi can operate with either .br fr=0 or .br fr=1 . .tp .br pr_fp_mode_fre enable emulation of 32-bit floating-point mode. when this mode is enabled, it emulates 32-bit floating-point operations by raising a reserved-instruction exception on every instruction that uses 32-bit formats and the kernel then handles the instruction in software. (the problem lies in the discrepancy of handling odd-numbered registers which are the high 32 bits of 64-bit registers with even numbers in .b fr=0 mode and the lower 32-bit parts of odd-numbered 64-bit registers in .b fr=1 mode.) enabling this bit is necessary when code with the o32 fp32 abi should operate with code with compatible the o32 fpxx or o32 fp64a abis (which require .b fr=1 fpu mode) or when it is executed on newer hardware (mips r6 onwards) which lacks .b fr=0 mode support when a binary with the fp32 abi is used. .ip note that this mode makes sense only when the fpu is in 64-bit mode .rb ( fr=1 ). .ip note that the use of emulation inherently has a significant performance hit and should be avoided if possible. .re .ip in the n32/n64 abi, 64-bit floating-point mode is always used, so fpu emulation is not required and the fpu always operates in .b fr=1 mode. .ip this option is mainly intended for use by the dynamic linker .rb ( ld.so (8)). .ip the arguments .ir arg3 , .ir arg4 , and .ir arg5 are ignored. .\" prctl pr_get_fp_mode .tp .br pr_get_fp_mode " (since linux 4.0, only on mips)" return (as the function result) the current floating-point mode (see the description of .b pr_set_fp_mode for details). .ip on success, the call returns a bit mask which represents the current floating-point mode. .ip the arguments .ir arg2 , .ir arg3 , .ir arg4 , and .ir arg5 are ignored. .\" prctl pr_set_fpemu .tp .br pr_set_fpemu " (since linux 2.4.18, 2.5.9, only on ia64)" set floating-point emulation control bits to \fiarg2\fp. pass .b pr_fpemu_noprint to silently emulate floating-point operation accesses, or .b pr_fpemu_sigfpe to not emulate floating-point operations and send .b sigfpe instead. .\" prctl pr_get_fpemu .tp .br pr_get_fpemu " (since linux 2.4.18, 2.5.9, only on ia64)" return floating-point emulation control bits, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_fpexc .tp .br pr_set_fpexc " (since linux 2.4.21, 2.5.32, only on powerpc)" set floating-point exception mode to \fiarg2\fp. pass \fbpr_fp_exc_sw_enable\fp to use fpexc for fp exception enables, \fbpr_fp_exc_div\fp for floating-point divide by zero, \fbpr_fp_exc_ovf\fp for floating-point overflow, \fbpr_fp_exc_und\fp for floating-point underflow, \fbpr_fp_exc_res\fp for floating-point inexact result, \fbpr_fp_exc_inv\fp for floating-point invalid operation, \fbpr_fp_exc_disabled\fp for fp exceptions disabled, \fbpr_fp_exc_nonrecov\fp for async nonrecoverable exception mode, \fbpr_fp_exc_async\fp for async recoverable exception mode, \fbpr_fp_exc_precise\fp for precise exception mode. .\" prctl pr_get_fpexc .tp .br pr_get_fpexc " (since linux 2.4.21, 2.5.32, only on powerpc)" return floating-point exception mode, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_io_flusher .tp .br pr_set_io_flusher " (since linux 5.6)" if a user process is involved in the block layer or filesystem i/o path, and can allocate memory while processing i/o requests it must set \fiarg2\fp to 1. this will put the process in the io_flusher state, which allows it special treatment to make progress when allocating memory. if \fiarg2\fp is 0, the process will clear the io_flusher state, and the default behavior will be used. .ip the calling process must have the .br cap_sys_resource capability. .ip .ir arg3 , .ir arg4 , and .ir arg5 must be zero. .ip the io_flusher state is inherited by a child process created via .br fork (2) and is preserved across .br execve (2). .ip examples of io_flusher applications are fuse daemons, scsi device emulation daemons, and daemons that perform error handling like multipath path recovery applications. .\" prctl pr_get_io_flusher .tp .b pr_get_io_flusher (since linux 5.6) return (as the function result) the io_flusher state of the caller. a value of 1 indicates that the caller is in the io_flusher state; 0 indicates that the caller is not in the io_flusher state. .ip the calling process must have the .br cap_sys_resource capability. .ip .ir arg2 , .ir arg3 , .ir arg4 , and .ir arg5 must be zero. .\" prctl pr_set_keepcaps .tp .br pr_set_keepcaps " (since linux 2.2.18)" set the state of the calling thread's "keep capabilities" flag. the effect of this flag is described in .br capabilities (7). .i arg2 must be either 0 (clear the flag) or 1 (set the flag). the "keep capabilities" value will be reset to 0 on subsequent calls to .br execve (2). .\" prctl pr_get_keepcaps .tp .br pr_get_keepcaps " (since linux 2.2.18)" return (as the function result) the current state of the calling thread's "keep capabilities" flag. see .br capabilities (7) for a description of this flag. .\" prctl pr_mce_kill .tp .br pr_mce_kill " (since linux 2.6.32)" set the machine check memory corruption kill policy for the calling thread. if .i arg2 is .br pr_mce_kill_clear , clear the thread memory corruption kill policy and use the system-wide default. (the system-wide default is defined by .ir /proc/sys/vm/memory_failure_early_kill ; see .br proc (5).) if .i arg2 is .br pr_mce_kill_set , use a thread-specific memory corruption kill policy. in this case, .i arg3 defines whether the policy is .i early kill .rb ( pr_mce_kill_early ), .i late kill .rb ( pr_mce_kill_late ), or the system-wide default .rb ( pr_mce_kill_default ). early kill means that the thread receives a .b sigbus signal as soon as hardware memory corruption is detected inside its address space. in late kill mode, the process is killed only when it accesses a corrupted page. see .br sigaction (2) for more information on the .br sigbus signal. the policy is inherited by children. the remaining unused .br prctl () arguments must be zero for future compatibility. .\" prctl pr_mce_kill_get .tp .br pr_mce_kill_get " (since linux 2.6.32)" return (as the function result) the current per-process machine check kill policy. all unused .br prctl () arguments must be zero. .\" prctl pr_set_mm .tp .br pr_set_mm " (since linux 3.3)" .\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036 modify certain kernel memory map descriptor fields of the calling process. usually these fields are set by the kernel and dynamic loader (see .br ld.so (8) for more information) and a regular application should not use this feature. however, there are cases, such as self-modifying programs, where a program might find it useful to change its own memory map. .ip the calling process must have the .br cap_sys_resource capability. the value in .i arg2 is one of the options below, while .i arg3 provides a new value for the option. the .i arg4 and .i arg5 arguments must be zero if unused. .ip before linux 3.10, .\" commit 52b3694157e3aa6df871e283115652ec6f2d31e0 this feature is available only if the kernel is built with the .br config_checkpoint_restore option enabled. .rs .tp .br pr_set_mm_start_code set the address above which the program text can run. the corresponding memory area must be readable and executable, but not writable or shareable (see .br mprotect (2) and .br mmap (2) for more information). .tp .br pr_set_mm_end_code set the address below which the program text can run. the corresponding memory area must be readable and executable, but not writable or shareable. .tp .br pr_set_mm_start_data set the address above which initialized and uninitialized (bss) data are placed. the corresponding memory area must be readable and writable, but not executable or shareable. .tp .b pr_set_mm_end_data set the address below which initialized and uninitialized (bss) data are placed. the corresponding memory area must be readable and writable, but not executable or shareable. .tp .br pr_set_mm_start_stack set the start address of the stack. the corresponding memory area must be readable and writable. .tp .br pr_set_mm_start_brk set the address above which the program heap can be expanded with .br brk (2) call. the address must be greater than the ending address of the current program data segment. in addition, the combined size of the resulting heap and the size of the data segment can't exceed the .br rlimit_data resource limit (see .br setrlimit (2)). .tp .br pr_set_mm_brk set the current .br brk (2) value. the requirements for the address are the same as for the .br pr_set_mm_start_brk option. .pp the following options are available since linux 3.5. .\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7 .tp .br pr_set_mm_arg_start set the address above which the program command line is placed. .tp .br pr_set_mm_arg_end set the address below which the program command line is placed. .tp .br pr_set_mm_env_start set the address above which the program environment is placed. .tp .br pr_set_mm_env_end set the address below which the program environment is placed. .ip the address passed with .br pr_set_mm_arg_start , .br pr_set_mm_arg_end , .br pr_set_mm_env_start , and .br pr_set_mm_env_end should belong to a process stack area. thus, the corresponding memory area must be readable, writable, and (depending on the kernel configuration) have the .br map_growsdown attribute set (see .br mmap (2)). .tp .br pr_set_mm_auxv set a new auxiliary vector. the .i arg3 argument should provide the address of the vector. the .i arg4 is the size of the vector. .tp .br pr_set_mm_exe_file .\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6 supersede the .ir /proc/pid/exe symbolic link with a new one pointing to a new executable file identified by the file descriptor provided in .i arg3 argument. the file descriptor should be obtained with a regular .br open (2) call. .ip to change the symbolic link, one needs to unmap all existing executable memory areas, including those created by the kernel itself (for example the kernel usually creates at least one executable memory area for the elf .ir \.text section). .ip in linux 4.9 and earlier, the .\" commit 3fb4afd9a504c2386b8435028d43283216bf588e .br pr_set_mm_exe_file operation can be performed only once in a process's lifetime; attempting to perform the operation a second time results in the error .br eperm . this restriction was enforced for security reasons that were subsequently deemed specious, and the restriction was removed in linux 4.10 because some user-space applications needed to perform this operation more than once. .pp the following options are available since linux 3.18. .\" commit f606b77f1a9e362451aca8f81d8f36a3a112139e .tp .br pr_set_mm_map provides one-shot access to all the addresses by passing in a .i struct prctl_mm_map (as defined in \fi\fp). the .i arg4 argument should provide the size of the struct. .ip this feature is available only if the kernel is built with the .br config_checkpoint_restore option enabled. .tp .br pr_set_mm_map_size returns the size of the .i struct prctl_mm_map the kernel expects. this allows user space to find a compatible struct. the .i arg4 argument should be a pointer to an unsigned int. .ip this feature is available only if the kernel is built with the .br config_checkpoint_restore option enabled. .re .\" prctl pr_mpx_enable_management .tp .br pr_mpx_enable_management ", " pr_mpx_disable_management " (since linux 3.19, removed in linux 5.4; only on x86)" .\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c .\" see also http://lwn.net/articles/582712/ .\" see also https://gcc.gnu.org/wiki/intel%20mpx%20support%20in%20the%20gcc%20compiler enable or disable kernel management of memory protection extensions (mpx) bounds tables. the .ir arg2 , .ir arg3 , .ir arg4 , and .ir arg5 .\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88 arguments must be zero. .ip mpx is a hardware-assisted mechanism for performing bounds checking on pointers. it consists of a set of registers storing bounds information and a set of special instruction prefixes that tell the cpu on which instructions it should do bounds enforcement. there is a limited number of these registers and when there are more pointers than registers, their contents must be "spilled" into a set of tables. these tables are called "bounds tables" and the mpx .br prctl () operations control whether the kernel manages their allocation and freeing. .ip when management is enabled, the kernel will take over allocation and freeing of the bounds tables. it does this by trapping the #br exceptions that result at first use of missing bounds tables and instead of delivering the exception to user space, it allocates the table and populates the bounds directory with the location of the new table. for freeing, the kernel checks to see if bounds tables are present for memory which is not allocated, and frees them if so. .ip before enabling mpx management using .br pr_mpx_enable_management , the application must first have allocated a user-space buffer for the bounds directory and placed the location of that directory in the .i bndcfgu register. .ip these calls fail if the cpu or kernel does not support mpx. kernel support for mpx is enabled via the .br config_x86_intel_mpx configuration option. you can check whether the cpu supports mpx by looking for the .i mpx cpuid bit, like with the following command: .ip .in +4n .ex cat /proc/cpuinfo | grep \(aq mpx \(aq .ee .in .ip a thread may not switch in or out of long (64-bit) mode while mpx is enabled. .ip all threads in a process are affected by these calls. .ip the child of a .br fork (2) inherits the state of mpx management. during .br execve (2), mpx management is reset to a state as if .br pr_mpx_disable_management had been called. .ip for further information on intel mpx, see the kernel source file .ir documentation/x86/intel_mpx.txt . .ip .\" commit f240652b6032b48ad7fa35c5e701cc4c8d697c0b .\" see also https://lkml.kernel.org/r/20190705175321.db42f0ad@viggo.jf.intel.com due to a lack of toolchain support, .br pr_mpx_enable_management " and " pr_mpx_disable_management are not supported in linux 5.4 and later. .\" prctl pr_set_name .tp .br pr_set_name " (since linux 2.6.9)" set the name of the calling thread, using the value in the location pointed to by .ir "(char\ *) arg2" . the name can be up to 16 bytes long, .\" task_comm_len in include/linux/sched.h including the terminating null byte. (if the length of the string, including the terminating null byte, exceeds 16 bytes, the string is silently truncated.) this is the same attribute that can be set via .br pthread_setname_np (3) and retrieved using .br pthread_getname_np (3). the attribute is likewise accessible via .ir /proc/self/task/[tid]/comm (see .br proc (5)), where .i [tid] is the thread id of the calling thread, as returned by .br gettid (2). .\" prctl pr_get_name .tp .br pr_get_name " (since linux 2.6.11)" return the name of the calling thread, in the buffer pointed to by .ir "(char\ *) arg2" . the buffer should allow space for up to 16 bytes; the returned string will be null-terminated. .\" prctl pr_set_no_new_privs .tp .br pr_set_no_new_privs " (since linux 3.5)" set the calling thread's .i no_new_privs attribute to the value in .ir arg2 . with .i no_new_privs set to 1, .br execve (2) promises not to grant privileges to do anything that could not have been done without the .br execve (2) call (for example, rendering the set-user-id and set-group-id mode bits, and file capabilities non-functional). once set, the .i no_new_privs attribute cannot be unset. the setting of this attribute is inherited by children created by .br fork (2) and .br clone (2), and preserved across .br execve (2). .ip since linux 4.10, the value of a thread's .i no_new_privs attribute can be viewed via the .i nonewprivs field in the .ir /proc/[pid]/status file. .ip for more information, see the kernel source file .ir documentation/userspace\-api/no_new_privs.rst .\" commit 40fde647ccb0ae8c11d256d271e24d385eed595b (or .ir documentation/prctl/no_new_privs.txt before linux 4.13). see also .br seccomp (2). .\" prctl pr_get_no_new_privs .tp .br pr_get_no_new_privs " (since linux 3.5)" return (as the function result) the value of the .i no_new_privs attribute for the calling thread. a value of 0 indicates the regular .br execve (2) behavior. a value of 1 indicates .br execve (2) will operate in the privilege-restricting mode described above. .\" prctl pr_pac_reset_keys .\" commit ba830885656414101b2f8ca88786524d4bb5e8c1 .tp .br pr_pac_reset_keys " (since linux 5.0, only on arm64)" securely reset the thread's pointer authentication keys to fresh random values generated by the kernel. .ip the set of keys to be reset is specified by .ir arg2 , which must be a logical or of zero or more of the following: .rs .tp .b pr_pac_apiakey instruction authentication key a .tp .b pr_pac_apibkey instruction authentication key b .tp .b pr_pac_apdakey data authentication key a .tp .b pr_pac_apdbkey data authentication key b .tp .b pr_pac_apgakey generic authentication \(lqa\(rq key. .ip (yes folks, there really is no generic b key.) .re .ip as a special case, if .i arg2 is zero, then all the keys are reset. since new keys could be added in future, this is the recommended way to completely wipe the existing keys when establishing a clean execution context. note that there is no need to use .br pr_pac_reset_keys in preparation for calling .br execve (2), since .br execve (2) resets all the pointer authentication keys. .ip the remaining arguments .ir arg3 ", " arg4 ", and " arg5 must all be zero. .ip if the arguments are invalid, and in particular if .i arg2 contains set bits that are unrecognized or that correspond to a key not available on this platform, then the call fails with error .br einval . .ip .b warning: because the compiler or run-time environment may be using some or all of the keys, a successful .b pr_pac_reset_keys may crash the calling process. the conditions for using it safely are complex and system-dependent. don't use it unless you know what you are doing. .ip for more information, see the kernel source file .i documentation/arm64/pointer\-authentication.rst .\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed (or .i documentation/arm64/pointer\-authentication.txt before linux 5.3). .\" prctl pr_set_pdeathsig .tp .br pr_set_pdeathsig " (since linux 2.1.57)" set the parent-death signal of the calling process to \fiarg2\fp (either a signal value in the range 1..\c .br nsig "\-1" , or 0 to clear). this is the signal that the calling process will get when its parent dies. .ip .ir warning : .\" https://bugzilla.kernel.org/show_bug.cgi?id=43300 the "parent" in this case is considered to be the .i thread that created this process. in other words, the signal will be sent when that thread terminates (via, for example, .br pthread_exit (3)), rather than after all of the threads in the parent process terminate. .ip the parent-death signal is sent upon subsequent termination of the parent thread and also upon termination of each subreaper process (see the description of .b pr_set_child_subreaper above) to which the caller is subsequently reparented. if the parent thread and all ancestor subreapers have already terminated by the time of the .br pr_set_pdeathsig operation, then no parent-death signal is sent to the caller. .ip the parent-death signal is process-directed (see .br signal (7)) and, if the child installs a handler using the .br sigaction (2) .b sa_siginfo flag, the .i si_pid field of the .i siginfo_t argument of the handler contains the pid of the terminating parent process. .ip the parent-death signal setting is cleared for the child of a .br fork (2). it is also (since linux 2.4.36 / 2.6.23) .\" commit d2d56c5f51028cb9f3d800882eb6f4cbd3f9099f cleared when executing a set-user-id or set-group-id binary, or a binary that has associated capabilities (see .br capabilities (7)); otherwise, this value is preserved across .br execve (2). the parent-death signal setting is also cleared upon changes to any of the following thread credentials: .\" fixme capability changes can also trigger this; see .\" kernel/cred.c::commit_creds in the linux 5.6 source. effective user id, effective group id, filesystem user id, or filesystem group id. .\" prctl pr_get_pdeathsig .tp .br pr_get_pdeathsig " (since linux 2.3.15)" return the current value of the parent process death signal, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_ptracer .tp .br pr_set_ptracer " (since linux 3.4)" .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb .\" commit bf06189e4d14641c0148bea16e9dd24943862215 this is meaningful only when the yama lsm is enabled and in mode 1 ("restricted ptrace", visible via .ir /proc/sys/kernel/yama/ptrace_scope ). when a "ptracer process id" is passed in \fiarg2\fp, the caller is declaring that the ptracer process can .br ptrace (2) the calling process as if it were a direct process ancestor. each .b pr_set_ptracer operation replaces the previous "ptracer process id". employing .b pr_set_ptracer with .i arg2 set to 0 clears the caller's "ptracer process id". if .i arg2 is .br pr_set_ptracer_any , the ptrace restrictions introduced by yama are effectively disabled for the calling process. .ip for further information, see the kernel source file .ir documentation/admin\-guide/lsm/yama.rst .\" commit 90bb766440f2147486a2acc3e793d7b8348b0c22 (or .ir documentation/security/yama.txt before linux 4.13). .\" prctl pr_set_seccomp .tp .br pr_set_seccomp " (since linux 2.6.23)" .\" see http://thread.gmane.org/gmane.linux.kernel/542632 .\" [patch 0 of 2] seccomp updates .\" andrea@cpushare.com set the secure computing (seccomp) mode for the calling thread, to limit the available system calls. the more recent .br seccomp (2) system call provides a superset of the functionality of .br pr_set_seccomp . .ip the seccomp mode is selected via .ir arg2 . (the seccomp constants are defined in .ir .) .ip with .ir arg2 set to .br seccomp_mode_strict , the only system calls that the thread is permitted to make are .br read (2), .br write (2), .br _exit (2) (but not .br exit_group (2)), and .br sigreturn (2). other system calls result in the delivery of a .br sigkill signal. strict secure computing mode is useful for number-crunching applications that may need to execute untrusted byte code, perhaps obtained by reading from a pipe or socket. this operation is available only if the kernel is configured with .b config_seccomp enabled. .ip with .ir arg2 set to .br seccomp_mode_filter " (since linux 3.5)," the system calls allowed are defined by a pointer to a berkeley packet filter passed in .ir arg3 . this argument is a pointer to .ir "struct sock_fprog" ; it can be designed to filter arbitrary system calls and system call arguments. this mode is available only if the kernel is configured with .b config_seccomp_filter enabled. .ip if .br seccomp_mode_filter filters permit .br fork (2), then the seccomp mode is inherited by children created by .br fork (2); if .br execve (2) is permitted, then the seccomp mode is preserved across .br execve (2). if the filters permit .br prctl () calls, then additional filters can be added; they are run in order until the first non-allow result is seen. .ip for further information, see the kernel source file .ir documentation/userspace\-api/seccomp_filter.rst .\" commit c061f33f35be0ccc80f4b8e0aea5dfd2ed7e01a3 (or .ir documentation/prctl/seccomp_filter.txt before linux 4.13). .\" prctl pr_get_seccomp .tp .br pr_get_seccomp " (since linux 2.6.23)" return (as the function result) the secure computing mode of the calling thread. if the caller is not in secure computing mode, this operation returns 0; if the caller is in strict secure computing mode, then the .br prctl () call will cause a .b sigkill signal to be sent to the process. if the caller is in filter mode, and this system call is allowed by the seccomp filters, it returns 2; otherwise, the process is killed with a .br sigkill signal. this operation is available only if the kernel is configured with .b config_seccomp enabled. .ip since linux 3.8, the .ir seccomp field of the .ir /proc/[pid]/status file provides a method of obtaining the same information, without the risk that the process is killed; see .br proc (5). .\" prctl pr_set_securebits .tp .br pr_set_securebits " (since linux 2.6.26)" set the "securebits" flags of the calling thread to the value supplied in .ir arg2 . see .br capabilities (7). .\" prctl pr_get_securebits .tp .br pr_get_securebits " (since linux 2.6.26)" return (as the function result) the "securebits" flags of the calling thread. see .br capabilities (7). .\" prctl pr_get_speculation_ctrl .tp .br pr_get_speculation_ctrl " (since linux 4.17)" return (as the function result) the state of the speculation misfeature specified in .ir arg2 . currently, the only permitted value for this argument is .br pr_spec_store_bypass (otherwise the call fails with the error .br enodev ). .ip the return value uses bits 0-3 with the following meaning: .rs .tp .br pr_spec_prctl mitigation can be controlled per thread by .br pr_set_speculation_ctrl . .tp .br pr_spec_enable the speculation feature is enabled, mitigation is disabled. .tp .br pr_spec_disable the speculation feature is disabled, mitigation is enabled. .tp .br pr_spec_force_disable same as .b pr_spec_disable but cannot be undone. .tp .br pr_spec_disable_noexec " (since linux 5.1)" same as .br pr_spec_disable , but the state will be cleared on .br execve (2). .re .ip if all bits are 0, then the cpu is not affected by the speculation misfeature. .ip if .b pr_spec_prctl is set, then per-thread control of the mitigation is available. if not set, .br prctl () for the speculation misfeature will fail. .ip the .ir arg3 , .ir arg4 , and .i arg5 arguments must be specified as 0; otherwise the call fails with the error .br einval . .\" prctl pr_set_speculation_ctrl .tp .br pr_set_speculation_ctrl " (since linux 4.17)" .\" commit b617cfc858161140d69cc0b5cc211996b557a1c7 .\" commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee sets the state of the speculation misfeature specified in .ir arg2 . the speculation-misfeature settings are per-thread attributes. .ip currently, .i arg2 must be one of: .rs .tp .b pr_spec_store_bypass set the state of the speculative store bypass misfeature. .\" commit 9137bb27e60e554dab694eafa4cca241fa3a694f .tp .br pr_spec_indirect_branch " (since linux 4.20)" set the state of the indirect branch speculation misfeature. .re .ip if .i arg2 does not have one of the above values, then the call fails with the error .br enodev . .ip the .ir arg3 argument is used to hand in the control value, which is one of the following: .rs .tp .br pr_spec_enable the speculation feature is enabled, mitigation is disabled. .tp .br pr_spec_disable the speculation feature is disabled, mitigation is enabled. .tp .br pr_spec_force_disable same as .br pr_spec_disable , but cannot be undone. a subsequent .br prctl (\c .ir arg2 , .br pr_spec_enable ) with the same value for .i arg2 will fail with the error .br eperm . .\" commit 71368af9027f18fe5d1c6f372cfdff7e4bde8b48 .tp .br pr_spec_disable_noexec " (since linux 5.1)" same as .br pr_spec_disable , but the state will be cleared on .br execve (2). currently only supported for .i arg2 equal to .b pr_spec_store_bypass. .re .ip any unsupported value in .ir arg3 will result in the call failing with the error .br erange . .ip the .i arg4 and .i arg5 arguments must be specified as 0; otherwise the call fails with the error .br einval . .ip the speculation feature can also be controlled by the .b spec_store_bypass_disable boot parameter. this parameter may enforce a read-only policy which will result in the .br prctl () call failing with the error .br enxio . for further details, see the kernel source file .ir documentation/admin\-guide/kernel\-parameters.txt . .\" prctl pr_sve_set_vl .\" commit 2d2123bc7c7f843aa9db87720de159a049839862 .\" linux-5.6/documentation/arm64/sve.rst .tp .br pr_sve_set_vl " (since linux 4.15, only on arm64)" configure the thread's sve vector length, as specified by .ir "(int) arg2" . arguments .ir arg3 ", " arg4 ", and " arg5 are ignored. .ip the bits of .i arg2 corresponding to .b pr_sve_vl_len_mask must be set to the desired vector length in bytes. this is interpreted as an upper bound: the kernel will select the greatest available vector length that does not exceed the value specified. in particular, specifying .b sve_vl_max (defined in .i ) for the .b pr_sve_vl_len_mask bits requests the maximum supported vector length. .ip in addition, the other bits of .i arg2 must be set to one of the following combinations of flags: .rs .tp .b 0 perform the change immediately. at the next .br execve (2) in the thread, the vector length will be reset to the value configured in .ir /proc/sys/abi/sve_default_vector_length . .tp .b pr_sve_vl_inherit perform the change immediately. subsequent .br execve (2) calls will preserve the new vector length. .tp .b pr_sve_set_vl_onexec defer the change, so that it is performed at the next .br execve (2) in the thread. further .br execve (2) calls will reset the vector length to the value configured in .ir /proc/sys/abi/sve_default_vector_length . .tp .b "pr_sve_set_vl_onexec | pr_sve_vl_inherit" defer the change, so that it is performed at the next .br execve (2) in the thread. further .br execve (2) calls will preserve the new vector length. .re .ip in all cases, any previously pending deferred change is canceled. .ip the call fails with error .b einval if sve is not supported on the platform, if .i arg2 is unrecognized or invalid, or the value in the bits of .i arg2 corresponding to .b pr_sve_vl_len_mask is outside the range .br sve_vl_min .. sve_vl_max or is not a multiple of 16. .ip on success, a nonnegative value is returned that describes the .i selected configuration. if .b pr_sve_set_vl_onexec was included in .ir arg2 , then the configuration described by the return value will take effect at the next .br execve (2). otherwise, the configuration is already in effect when the .b pr_sve_set_vl call returns. in either case, the value is encoded in the same way as the return value of .br pr_sve_get_vl . note that there is no explicit flag in the return value corresponding to .br pr_sve_set_vl_onexec . .ip the configuration (including any pending deferred change) is inherited across .br fork (2) and .br clone (2). .ip for more information, see the kernel source file .i documentation/arm64/sve.rst .\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed (or .i documentation/arm64/sve.txt before linux 5.3). .ip .b warning: because the compiler or run-time environment may be using sve, using this call without the .b pr_sve_set_vl_onexec flag may crash the calling process. the conditions for using it safely are complex and system-dependent. don't use it unless you really know what you are doing. .\" prctl pr_sve_get_vl .tp .br pr_sve_get_vl " (since linux 4.15, only on arm64)" get the thread's current sve vector length configuration. .ip arguments .ir arg2 ", " arg3 ", " arg4 ", and " arg5 are ignored. .ip provided that the kernel and platform support sve, this operation always succeeds, returning a nonnegative value that describes the .i current configuration. the bits corresponding to .b pr_sve_vl_len_mask contain the currently configured vector length in bytes. the bit corresponding to .b pr_sve_vl_inherit indicates whether the vector length will be inherited across .br execve (2). .ip note that there is no way to determine whether there is a pending vector length change that has not yet taken effect. .ip for more information, see the kernel source file .i documentation/arm64/sve.rst .\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed (or .i documentation/arm64/sve.txt before linux 5.3). .tp .\" prctl pr_set_syscall_user_dispatch .\" commit 1446e1df9eb183fdf81c3f0715402f1d7595d4 .br pr_set_syscall_user_dispatch " (since linux 5.11, x86 only)" configure the syscall user dispatch mechanism for the calling thread. this mechanism allows an application to selectively intercept system calls so that they can be handled within the application itself. interception takes the form of a thread-directed .b sigsys signal that is delivered to the thread when it makes a system call. if intercepted, the system call is not executed by the kernel. .ip to enable this mechanism, .i arg2 should be set to .br pr_sys_dispatch_on . once enabled, further system calls will be selectively intercepted, depending on a control variable provided by user space. in this case, .i arg3 and .i arg4 respectively identify the .i offset and .i length of a single contiguous memory region in the process address space from where system calls are always allowed to be executed, regardless of the control variable. (typically, this area would include the area of memory containing the c library.) .ip .i arg5 points to a char-sized variable that is a fast switch to allow/block system call execution without the overhead of doing another system call to re-configure syscall user dispatch. this control variable can either be set to .b syscall_dispatch_filter_block to block system calls from executing or to .b syscall_dispatch_filter_allow to temporarily allow them to be executed. this value is checked by the kernel on every system call entry, and any unexpected value will raise an uncatchable .b sigsys at that time, killing the application. .ip when a system call is intercepted, the kernel sends a thread-directed .b sigsys signal to the triggering thread. various fields will be set in the .i siginfo_t structure (see .br sigaction (2)) associated with the signal: .rs .ip * 3 .i si_signo will contain .br sigsys . .ip * .ir si_call_addr will show the address of the system call instruction. .ip * .ir si_syscall and .ir si_arch will indicate which system call was attempted. .ip * .i si_code will contain .br sys_user_dispatch . .ip * .i si_errno will be set to 0. .re .ip the program counter will be as though the system call happened (i.e., the program counter will not point to the system call instruction). .ip when the signal handler returns to the kernel, the system call completes immediately and returns to the calling thread, without actually being executed. if necessary (i.e., when emulating the system call on user space.), the signal handler should set the system call return value to a sane value, by modifying the register context stored in the .i ucontext argument of the signal handler. see .br sigaction (2), .br sigreturn (2), and .br getcontext (3) for more information. .ip if .i arg2 is set to .br pr_sys_dispatch_off , syscall user dispatch is disabled for that thread. the remaining arguments must be set to 0. .ip the setting is not preserved across .br fork (2), .br clone (2), or .br execve (2). .ip for more information, see the kernel source file .ir documentation/admin-guide/syscall-user-dispatch.rst .\" prctl pr_set_tagged_addr_ctrl .\" commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d .tp .br pr_set_tagged_addr_ctrl " (since linux 5.4, only on arm64)" controls support for passing tagged user-space addresses to the kernel (i.e., addresses where bits 56\(em63 are not all zero). .ip the level of support is selected by .ir "arg2" , which can be one of the following: .rs .tp .b 0 addresses that are passed for the purpose of being dereferenced by the kernel must be untagged. .tp .b pr_tagged_addr_enable addresses that are passed for the purpose of being dereferenced by the kernel may be tagged, with the exceptions summarized below. .re .ip the remaining arguments .ir arg3 ", " arg4 ", and " arg5 must all be zero. .\" enforcement added in .\" commit 3e91ec89f527b9870fe42dcbdb74fd389d123a95 .ip on success, the mode specified in .i arg2 is set for the calling thread and the return value is 0. if the arguments are invalid, the mode specified in .i arg2 is unrecognized, or if this feature is unsupported by the kernel or disabled via .ir /proc/sys/abi/tagged_addr_disabled , the call fails with the error .br einval . .ip in particular, if .br prctl ( pr_set_tagged_addr_ctrl , 0, 0, 0, 0) fails with .br einval , then all addresses passed to the kernel must be untagged. .ip irrespective of which mode is set, addresses passed to certain interfaces must always be untagged: .rs .ip \(bu 2 .br brk (2), .br mmap (2), .br shmat (2), .br shmdt (2), and the .i new_address argument of .br mremap (2). .ip (prior to linux 5.6 these accepted tagged addresses, but the behaviour may not be what you expect. don't rely on it.) .ip \(bu \(oqpolymorphic\(cq interfaces that accept pointers to arbitrary types cast to a .i void * or other generic type, specifically .br prctl (), .br ioctl (2), and in general .br setsockopt (2) (only certain specific .br setsockopt (2) options allow tagged addresses). .re .ip this list of exclusions may shrink when moving from one kernel version to a later kernel version. while the kernel may make some guarantees for backwards compatibility reasons, for the purposes of new software the effect of passing tagged addresses to these interfaces is unspecified. .ip the mode set by this call is inherited across .br fork (2) and .br clone (2). the mode is reset by .br execve (2) to 0 (i.e., tagged addresses not permitted in the user/kernel abi). .ip for more information, see the kernel source file .ir documentation/arm64/tagged\-address\-abi.rst . .ip .b warning: this call is primarily intended for use by the run-time environment. a successful .b pr_set_tagged_addr_ctrl call elsewhere may crash the calling process. the conditions for using it safely are complex and system-dependent. don't use it unless you know what you are doing. .\" prctl pr_get_tagged_addr_ctrl .\" commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d .tp .br pr_get_tagged_addr_ctrl " (since linux 5.4, only on arm64)" returns the current tagged address mode for the calling thread. .ip arguments .ir arg2 ", " arg3 ", " arg4 ", and " arg5 must all be zero. .ip if the arguments are invalid or this feature is disabled or unsupported by the kernel, the call fails with .br einval . in particular, if .br prctl ( pr_get_tagged_addr_ctrl , 0, 0, 0, 0) fails with .br einval , then this feature is definitely either unsupported, or disabled via .ir /proc/sys/abi/tagged_addr_disabled . in this case, all addresses passed to the kernel must be untagged. .ip otherwise, the call returns a nonnegative value describing the current tagged address mode, encoded in the same way as the .i arg2 argument of .br pr_set_tagged_addr_ctrl . .ip for more information, see the kernel source file .ir documentation/arm64/tagged\-address\-abi.rst . .\" .\" prctl pr_task_perf_events_disable .tp .br pr_task_perf_events_disable " (since linux 2.6.31)" disable all performance counters attached to the calling process, regardless of whether the counters were created by this process or another process. performance counters created by the calling process for other processes are unaffected. for more information on performance counters, see the linux kernel source file .ir tools/perf/design.txt . .ip originally called .br pr_task_perf_counters_disable ; .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28 renamed (retaining the same numerical value) in linux 2.6.32. .\" .\" prctl pr_task_perf_events_enable .tp .br pr_task_perf_events_enable " (since linux 2.6.31)" the converse of .br pr_task_perf_events_disable ; enable performance counters attached to the calling process. .ip originally called .br pr_task_perf_counters_enable ; .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28 renamed .\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6 in linux 2.6.32. .\" .\" prctl pr_set_thp_disable .tp .br pr_set_thp_disable " (since linux 3.15)" .\" commit a0715cc22601e8830ace98366c0c2bd8da52af52 set the state of the "thp disable" flag for the calling thread. if .i arg2 has a nonzero value, the flag is set, otherwise it is cleared. setting this flag provides a method for disabling transparent huge pages for jobs where the code cannot be modified, and using a malloc hook with .br madvise (2) is not an option (i.e., statically allocated data). the setting of the "thp disable" flag is inherited by a child created via .br fork (2) and is preserved across .br execve (2). .\" prctl pr_get_thp_disable .tp .br pr_get_thp_disable " (since linux 3.15)" return (as the function result) the current setting of the "thp disable" flag for the calling thread: either 1, if the flag is set, or 0, if it is not. .\" prctl pr_get_tid_address .tp .br pr_get_tid_address " (since linux 3.5)" .\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d return the .i clear_child_tid address set by .br set_tid_address (2) and the .br clone (2) .b clone_child_cleartid flag, in the location pointed to by .ir "(int\ **)\ arg2" . this feature is available only if the kernel is built with the .br config_checkpoint_restore option enabled. note that since the .br prctl () system call does not have a compat implementation for the amd64 x32 and mips n32 abis, and the kernel writes out a pointer using the kernel's pointer size, this operation expects a user-space buffer of 8 (not 4) bytes on these abis. .\" prctl pr_set_timerslack .tp .br pr_set_timerslack " (since linux 2.6.28)" .\" see https://lwn.net/articles/369549/ .\" commit 6976675d94042fbd446231d1bd8b7de71a980ada each thread has two associated timer slack values: a "default" value, and a "current" value. this operation sets the "current" timer slack value for the calling thread. .i arg2 is an unsigned long value, then maximum "current" value is ulong_max and the minimum "current" value is 1. if the nanosecond value supplied in .ir arg2 is greater than zero, then the "current" value is set to this value. if .i arg2 is equal to zero, the "current" timer slack is reset to the thread's "default" timer slack value. .ip the "current" timer slack is used by the kernel to group timer expirations for the calling thread that are close to one another; as a consequence, timer expirations for the thread may be up to the specified number of nanoseconds late (but will never expire early). grouping timer expirations can help reduce system power consumption by minimizing cpu wake-ups. .ip the timer expirations affected by timer slack are those set by .br select (2), .br pselect (2), .br poll (2), .br ppoll (2), .br epoll_wait (2), .br epoll_pwait (2), .br clock_nanosleep (2), .br nanosleep (2), and .br futex (2) (and thus the library functions implemented via futexes, including .\" list obtained by grepping for futex usage in glibc source .br pthread_cond_timedwait (3), .br pthread_mutex_timedlock (3), .br pthread_rwlock_timedrdlock (3), .br pthread_rwlock_timedwrlock (3), and .br sem_timedwait (3)). .ip timer slack is not applied to threads that are scheduled under a real-time scheduling policy (see .br sched_setscheduler (2)). .ip when a new thread is created, the two timer slack values are made the same as the "current" value of the creating thread. thereafter, a thread can adjust its "current" timer slack value via .br pr_set_timerslack . the "default" value can't be changed. the timer slack values of .ir init (pid 1), the ancestor of all processes, are 50,000 nanoseconds (50 microseconds). the timer slack value is inherited by a child created via .br fork (2), and is preserved across .br execve (2). .ip since linux 4.6, the "current" timer slack value of any process can be examined and changed via the file .ir /proc/[pid]/timerslack_ns . see .br proc (5). .\" prctl pr_get_timerslack .tp .br pr_get_timerslack " (since linux 2.6.28)" return (as the function result) the "current" timer slack value of the calling thread. .\" prctl pr_set_timing .tp .br pr_set_timing " (since linux 2.6.0)" .\" precisely: linux 2.6.0-test4 set whether to use (normal, traditional) statistical process timing or accurate timestamp-based process timing, by passing .b pr_timing_statistical .\" 0 or .b pr_timing_timestamp .\" 1 to \fiarg2\fp. .b pr_timing_timestamp is not currently implemented (attempting to set this mode will yield the error .br einval ). .\" pr_timing_timestamp doesn't do anything in 2.6.26-rc8, .\" and looking at the patch history, it appears .\" that it never did anything. .\" prctl pr_get_timing .tp .br pr_get_timing " (since linux 2.6.0)" .\" precisely: linux 2.6.0-test4 return (as the function result) which process timing method is currently in use. .\" prctl pr_set_tsc .tp .br pr_set_tsc " (since linux 2.6.26, x86 only)" set the state of the flag determining whether the timestamp counter can be read by the process. pass .b pr_tsc_enable to .i arg2 to allow it to be read, or .b pr_tsc_sigsegv to generate a .b sigsegv when the process tries to read the timestamp counter. .\" prctl pr_get_tsc .tp .br pr_get_tsc " (since linux 2.6.26, x86 only)" return the state of the flag determining whether the timestamp counter can be read, in the location pointed to by .ir "(int\ *) arg2" . .\" prctl pr_set_unalign .tp .b pr_set_unalign (only on: ia64, since linux 2.3.48; parisc, since linux 2.6.15; powerpc, since linux 2.6.18; alpha, since linux 2.6.22; .\" sh: 94ea5e449ae834af058ef005d16a8ad44fcf13d6 .\" tile: 2f9ac29eec71a696cb0dcc5fb82c0f8d4dac28c9 sh, since linux 2.6.34; tile, since linux 3.12) set unaligned access control bits to \fiarg2\fp. pass \fbpr_unalign_noprint\fp to silently fix up unaligned user accesses, or \fbpr_unalign_sigbus\fp to generate .b sigbus on unaligned user access. alpha also supports an additional flag with the value of 4 and no corresponding named constant, which instructs kernel to not fix up unaligned accesses (it is analogous to providing the .br uac_nofix flag in .br ssi_nvpairs operation of the .br setsysinfo () system call on tru64). .\" prctl pr_get_unalign .tp .b pr_get_unalign (see .b pr_set_unalign for information on versions and architectures.) return unaligned access control bits, in the location pointed to by .ir "(unsigned int\ *) arg2" . .sh return value on success, .br pr_cap_ambient + pr_cap_ambient_is_set , .br pr_capbset_read , .br pr_get_dumpable , .br pr_get_fp_mode , .br pr_get_io_flusher , .br pr_get_keepcaps , .br pr_mce_kill_get , .br pr_get_no_new_privs , .br pr_get_securebits , .br pr_get_speculation_ctrl , .br pr_sve_get_vl , .br pr_sve_set_vl , .br pr_get_tagged_addr_ctrl , .br pr_get_thp_disable , .br pr_get_timing , .br pr_get_timerslack , and (if it returns) .br pr_get_seccomp return the nonnegative values described above. all other .i option values return 0 on success. on error, \-1 is returned, and .i errno is set to indicate the error. .sh errors .tp .b eacces .i option is .br pr_set_seccomp and .i arg2 is .br seccomp_mode_filter , but the process does not have the .br cap_sys_admin capability or has not set the .ir no_new_privs attribute (see the discussion of .br pr_set_no_new_privs above). .tp .b eacces .i option is .br pr_set_mm , and .i arg3 is .br pr_set_mm_exe_file , the file is not executable. .tp .b ebadf .i option is .br pr_set_mm , .i arg3 is .br pr_set_mm_exe_file , and the file descriptor passed in .i arg4 is not valid. .tp .b ebusy .i option is .br pr_set_mm , .i arg3 is .br pr_set_mm_exe_file , and this the second attempt to change the .i /proc/pid/exe symbolic link, which is prohibited. .tp .b efault .i arg2 is an invalid address. .tp .b efault .i option is .br pr_set_seccomp , .i arg2 is .br seccomp_mode_filter , the system was built with .br config_seccomp_filter , and .i arg3 is an invalid address. .tp .b efault .i option is .b pr_set_syscall_user_dispatch and .i arg5 has an invalid address. .tp .b einval the value of .i option is not recognized, or not supported on this system. .tp .b einval .i option is .br pr_mce_kill or .br pr_mce_kill_get or .br pr_set_mm , and unused .br prctl () arguments were not specified as zero. .tp .b einval .i arg2 is not valid value for this .ir option . .tp .b einval .i option is .br pr_set_seccomp or .br pr_get_seccomp , and the kernel was not configured with .br config_seccomp . .tp .b einval .i option is .br pr_set_seccomp , .i arg2 is .br seccomp_mode_filter , and the kernel was not configured with .br config_seccomp_filter . .tp .b einval .i option is .br pr_set_mm , and one of the following is true .rs .ip * 3 .i arg4 or .i arg5 is nonzero; .ip * .i arg3 is greater than .b task_size (the limit on the size of the user address space for this architecture); .ip * .i arg2 is .br pr_set_mm_start_code , .br pr_set_mm_end_code , .br pr_set_mm_start_data , .br pr_set_mm_end_data , or .br pr_set_mm_start_stack , and the permissions of the corresponding memory area are not as required; .ip * .i arg2 is .br pr_set_mm_start_brk or .br pr_set_mm_brk , and .i arg3 is less than or equal to the end of the data segment or specifies a value that would cause the .b rlimit_data resource limit to be exceeded. .re .tp .b einval .i option is .br pr_set_ptracer and .i arg2 is not 0, .br pr_set_ptracer_any , or the pid of an existing process. .tp .b einval .i option is .b pr_set_pdeathsig and .i arg2 is not a valid signal number. .tp .b einval .i option is .br pr_set_dumpable and .i arg2 is neither .b suid_dump_disable nor .br suid_dump_user . .tp .b einval .i option is .br pr_set_timing and .i arg2 is not .br pr_timing_statistical . .tp .b einval .i option is .br pr_set_no_new_privs and .i arg2 is not equal to 1 or .ir arg3 , .ir arg4 , or .ir arg5 is nonzero. .tp .b einval .i option is .br pr_get_no_new_privs and .ir arg2 , .ir arg3 , .ir arg4 , or .ir arg5 is nonzero. .tp .b einval .i option is .br pr_set_thp_disable and .ir arg3 , .ir arg4 , or .ir arg5 is nonzero. .tp .b einval .i option is .br pr_get_thp_disable and .ir arg2 , .ir arg3 , .ir arg4 , or .ir arg5 is nonzero. .tp .b einval .i option is .b pr_cap_ambient and an unused argument .ri ( arg4 , .ir arg5 , or, in the case of .br pr_cap_ambient_clear_all , .ir arg3 ) is nonzero; or .ir arg2 has an invalid value; or .ir arg2 is .br pr_cap_ambient_lower , .br pr_cap_ambient_raise , or .br pr_cap_ambient_is_set and .ir arg3 does not specify a valid capability. .tp .b einval .i option was .br pr_get_speculation_ctrl or .br pr_set_speculation_ctrl and unused arguments to .br prctl () are not 0. .b einval .i option is .b pr_pac_reset_keys and the arguments are invalid or unsupported. see the description of .b pr_pac_reset_keys above for details. .tp .b einval .i option is .b pr_sve_set_vl and the arguments are invalid or unsupported, or sve is not available on this platform. see the description of .b pr_sve_set_vl above for details. .tp .b einval .i option is .b pr_sve_get_vl and sve is not available on this platform. .tp .b einval .i option is .b pr_set_syscall_user_dispatch and one of the following is true: .rs .ip * 3 .i arg2 is .b pr_sys_dispatch_off and the remaining arguments are not 0; .ip * 3 .i arg2 is .b pr_sys_dispatch_on and the memory range specified is outside the address space of the process. .ip * 3 .i arg2 is invalid. .re .tp .b einval .i option is .br pr_set_tagged_addr_ctrl and the arguments are invalid or unsupported. see the description of .b pr_set_tagged_addr_ctrl above for details. .tp .b einval .i option is .br pr_get_tagged_addr_ctrl and the arguments are invalid or unsupported. see the description of .b pr_get_tagged_addr_ctrl above for details. .tp .b enodev .i option was .br pr_set_speculation_ctrl the kernel or cpu does not support the requested speculation misfeature. .tp .b enxio .i option was .br pr_mpx_enable_management or .br pr_mpx_disable_management and the kernel or the cpu does not support mpx management. check that the kernel and processor have mpx support. .tp .b enxio .i option was .br pr_set_speculation_ctrl implies that the control of the selected speculation misfeature is not possible. see .br pr_get_speculation_ctrl for the bit fields to determine which option is available. .tp .b eopnotsupp .i option is .b pr_set_fp_mode and .i arg2 has an invalid or unsupported value. .tp .b eperm .i option is .br pr_set_securebits , and the caller does not have the .b cap_setpcap capability, or tried to unset a "locked" flag, or tried to set a flag whose corresponding locked flag was set (see .br capabilities (7)). .tp .b eperm .i option is .br pr_set_speculation_ctrl wherein the speculation was disabled with .b pr_spec_force_disable and caller tried to enable it again. .tp .b eperm .i option is .br pr_set_keepcaps , and the caller's .b secbit_keep_caps_locked flag is set (see .br capabilities (7)). .tp .b eperm .i option is .br pr_capbset_drop , and the caller does not have the .b cap_setpcap capability. .tp .b eperm .i option is .br pr_set_mm , and the caller does not have the .b cap_sys_resource capability. .tp .b eperm .ir option is .br pr_cap_ambient and .ir arg2 is .br pr_cap_ambient_raise , but either the capability specified in .ir arg3 is not present in the process's permitted and inheritable capability sets, or the .b pr_cap_ambient_lower securebit has been set. .tp .b erange .i option was .br pr_set_speculation_ctrl and .ir arg3 is not .br pr_spec_enable , .br pr_spec_disable , .br pr_spec_force_disable , nor .br pr_spec_disable_noexec . .sh versions the .br prctl () system call was introduced in linux 2.1.57. .\" the library interface was added in glibc 2.0.6 .sh conforming to this call is linux-specific. irix has a .br prctl () system call (also introduced in linux 2.1.44 as irix_prctl on the mips architecture), with prototype .pp .in +4n .ex .bi "ptrdiff_t prctl(int " option ", int " arg2 ", int " arg3 ); .ee .in .pp and options to get the maximum number of processes per user, get the maximum number of processors the calling process can use, find out whether a specified process is currently blocked, get or set the maximum stack size, and so on. .sh see also .br signal (2), .br core (5) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .so man3/nextup.3 .so man3/insque.3 .\" copyright 2001 andries brouwer . .\" and copyright 2008, linux foundation, written by michael kerrisk .\" .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .th ceil 3 2021-03-22 "" "linux programmer's manual" .sh name ceil, ceilf, ceill \- ceiling function: smallest integral value not less than argument .sh synopsis .nf .b #include .pp .bi "double ceil(double " x ); .bi "float ceilf(float " x ); .bi "long double ceill(long double " x ); .fi .pp link with \fi\-lm\fp. .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br ceilf (), .br ceill (): .nf _isoc99_source || _posix_c_source >= 200112l || /* since glibc 2.19: */ _default_source || /* glibc <= 2.19: */ _bsd_source || _svid_source .fi .sh description these functions return the smallest integral value that is not less than .ir x . .pp for example, .ir ceil(0.5) is 1.0, and .ir ceil(\-0.5) is 0.0. .sh return value these functions return the ceiling of .ir x . .pp if .i x is integral, +0, \-0, nan, or infinite, .i x itself is returned. .sh errors no errors occur. posix.1-2001 documents a range error for overflows, but see notes. .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br ceil (), .br ceilf (), .br ceill () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to c99, posix.1-2001, posix.1-2008. .pp the variant returning .i double also conforms to svr4, 4.3bsd, c89. .sh notes susv2 and posix.1-2001 contain text about overflow (which might set .i errno to .br erange , or raise an .b fe_overflow exception). in practice, the result cannot overflow on any current machine, so this error-handling stuff is just nonsense. .\" the posix.1-2001 application usage section discusses this point. (more precisely, overflow can happen only when the maximum value of the exponent is smaller than the number of mantissa bits. for the ieee-754 standard 32-bit and 64-bit floating-point numbers the maximum value of the exponent is 128 (respectively, 1024), and the number of mantissa bits is 24 (respectively, 53).) .pp the integral value returned by these functions may be too large to store in an integer type .ri ( int , .ir long , etc.). to avoid an overflow, which will produce undefined results, an application should perform a range check on the returned value before assigning it to an integer type. .sh see also .br floor (3), .br lrint (3), .br nearbyint (3), .br rint (3), .br round (3), .br trunc (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/. .\" copyright 1993 david metcalfe (david@prism.demon.co.uk) .\" .\" %%%license_start(verbatim) .\" permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" since the linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. the author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. the author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%license_end .\" .\" references consulted: .\" linux libc source code .\" lewine's _posix programmer's guide_ (o'reilly & associates, 1991) .\" 386bsd man pages .\" modified sun mar 28 00:25:51 1993, david metcalfe .\" modified sat jul 24 18:13:39 1993 by rik faith (faith@cs.unc.edu) .\" modified sun aug 20 21:47:07 2000, aeb .\" .th random 3 2021-03-22 "gnu" "linux programmer's manual" .sh name random, srandom, initstate, setstate \- random number generator .sh synopsis .nf .b #include .pp .b long random(void); .bi "void srandom(unsigned int " seed ); .pp .bi "char *initstate(unsigned int " seed ", char *" state ", size_t " n ); .bi "char *setstate(char *" state ); .fi .pp .rs -4 feature test macro requirements for glibc (see .br feature_test_macros (7)): .re .pp .br random (), .br srandom (), .br initstate (), .br setstate (): .nf _xopen_source >= 500 .\" || _xopen_source && _xopen_source_extended || /* glibc since 2.19: */ _default_source || /* glibc <= 2.19: */ _svid_source || _bsd_source .fi .sh description the .br random () function uses a nonlinear additive feedback random number generator employing a default table of size 31 long integers to return successive pseudo-random numbers in the range from 0 to 2^31\ \-\ 1. the period of this random number generator is very large, approximately .ir "16\ *\ ((2^31)\ \-\ 1)" . .pp the .br srandom () function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by .br random (). these sequences are repeatable by calling .br srandom () with the same seed value. if no seed value is provided, the .br random () function is automatically seeded with a value of 1. .pp the .br initstate () function allows a state array \fistate\fp to be initialized for use by .br random (). the size of the state array \fin\fp is used by .br initstate () to decide how sophisticated a random number generator it should use\(emthe larger the state array, the better the random numbers will be. current "optimal" values for the size of the state array \fin\fp are 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to the nearest known amount. using less than 8 bytes results in an error. \fiseed\fp is the seed for the initialization, which specifies a starting point for the random number sequence, and provides for restarting at the same point. .pp the .br setstate () function changes the state array used by the .br random () function. the state array \fistate\fp is used for random number generation until the next call to .br initstate () or .br setstate (). \fistate\fp must first have been initialized using .br initstate () or be the result of a previous call of .br setstate (). .sh return value the .br random () function returns a value between 0 and .ir "(2^31)\ \-\ 1" . the .br srandom () function returns no value. .pp the .br initstate () function returns a pointer to the previous state array. on failure, it returns null, and .i errno is set to indicate the error. .pp on success, .br setstate () returns a pointer to the previous state array. on failure, it returns null, and .i errno is set to indicate the error. .sh errors .tp .b einval the .i state argument given to .br setstate () was null. .tp .b einval a state array of less than 8 bytes was specified to .br initstate (). .sh attributes for an explanation of the terms used in this section, see .br attributes (7). .ad l .nh .ts allbox; lbx lb lb l l l. interface attribute value t{ .br random (), .br srandom (), .br initstate (), .br setstate () t} thread safety mt-safe .te .hy .ad .sp 1 .sh conforming to posix.1-2001, posix.1-2008, 4.3bsd. .sh notes the .br random () function should not be used in multithreaded programs where reproducible behavior is required. use .br random_r (3) for that purpose. .pp random-number generation is a complex topic. .i numerical recipes in c: the art of scientific computing (william h.\& press, brian p.\& flannery, saul a.\& teukolsky, william t.\& vetterling; new york: cambridge university press, 2007, 3rd ed.) provides an excellent discussion of practical random-number generation issues in chapter 7 (random numbers). .pp for a more theoretical discussion which also covers many practical issues in depth, see chapter 3 (random numbers) in donald e.\& knuth's .ir "the art of computer programming" , volume 2 (seminumerical algorithms), 2nd ed.; reading, massachusetts: addison-wesley publishing company, 1981. .sh bugs according to posix, .br initstate () should return null on error. in the glibc implementation, .i errno is (as specified) set on error, but the function does not return null. .\" http://sourceware.org/bugzilla/show_bug.cgi?id=15380 .sh see also .br getrandom (2), .br drand48 (3), .br rand (3), .br random_r (3), .br srand (3) .sh colophon this page is part of release 5.13 of the linux .i man-pages project. a description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.