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sigqueue(3) — Linux manual page

sigqueue(3) Library Functions Manual sigqueue(3)

NAME top

 sigqueue - queue a signal and data to a process

LIBRARY top

 Standard C library (libc, -lc)

SYNOPSIS top

 #include <signal.h>
 int sigqueue(pid_t pid, int sig, const union sigval value);
 Feature Test Macro Requirements for glibc (see
 feature_test_macros(7)):
 sigqueue():
 _POSIX_C_SOURCE >= 199309L

DESCRIPTION top

 sigqueue() sends the signal specified in sig to the process whose
 PID is given in pid. The permissions required to send a signal
 are the same as for kill(2). As with kill(2), the null signal (0)
 can be used to check if a process with a given PID exists.
 The value argument is used to specify an accompanying item of data
 (either an integer or a pointer value) to be sent with the signal,
 and has the following type:
 union sigval {
 int sival_int;
 void *sival_ptr;
 };
 If the receiving process has installed a handler for this signal
 using the SA_SIGINFO flag to sigaction(2), then it can obtain this
 data via the si_value field of the siginfo_t structure passed as
 the second argument to the handler. Furthermore, the si_code
 field of that structure will be set to SI_QUEUE.

RETURN VALUE top

 On success, sigqueue() returns 0, indicating that the signal was
 successfully queued to the receiving process. Otherwise, -1 is
 returned and errno  is set to indicate the error.

ERRORS top

 EAGAIN The limit of signals which may be queued has been reached.
 (See signal(7) for further information.)
 EINVAL sig was invalid.
 EPERM The process does not have permission to send the signal to
 the receiving process. For the required permissions, see
 kill(2).
 ESRCH No process has a PID matching pid.

ATTRIBUTES top

 For an explanation of the terms used in this section, see
 attributes(7).
 ┌──────────────────────────────────────┬───────────────┬─────────┐
 │ Interface │ Attribute │ Value │
 ├──────────────────────────────────────┼───────────────┼─────────┤
 │ sigqueue() │ Thread safety │ MT-Safe │
 └──────────────────────────────────────┴───────────────┴─────────┘

VERSIONS top

 C library/kernel differences
 On Linux, sigqueue() is implemented using the rt_sigqueueinfo(2)
 system call. The system call differs in its third argument, which
 is the siginfo_t structure that will be supplied to the receiving
 process's signal handler or returned by the receiving process's
 sigtimedwait(2) call. Inside the glibc sigqueue() wrapper, this
 argument, uinfo, is initialized as follows:
 uinfo.si_signo = sig; /* Argument supplied to sigqueue() */
 uinfo.si_code = SI_QUEUE;
 uinfo.si_pid = getpid(); /* Process ID of sender */
 uinfo.si_uid = getuid(); /* Real UID of sender */
 uinfo.si_value = val; /* Argument supplied to sigqueue() */

STANDARDS top

 POSIX.1-2008.

HISTORY top

 Linux 2.2. POSIX.1-2001.

NOTES top

 If this function results in the sending of a signal to the process
 that invoked it, and that signal was not blocked by the calling
 thread, and no other threads were willing to handle this signal
 (either by having it unblocked, or by waiting for it using
 sigwait(3)), then at least some signal must be delivered to this
 thread before this function returns.

SEE ALSO top

 kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
 pthread_sigqueue(3), sigwait(3), signal(7)

COLOPHON top

 This page is part of the man-pages (Linux kernel and C library
 user-space interface documentation) project. Information about
 the project can be found at 
 ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
 for this manual page, see
 ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
 This page was obtained from the tarball man-pages-6.10.tar.gz
 fetched from
 ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
 2025年02月02日. If you discover any rendering problems in this HTML
 version of the page, or you believe there is a better or more up-
 to-date source for the page, or you have corrections or
 improvements to the information in this COLOPHON (which is not
 part of the original manual page), send a mail to
 man-pages@man7.org
Linux man-pages 6.10 2024年07月23日 sigqueue(3)

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Pages that refer to this page: kill(1), kill(1@@procps-ng), pgrep(1), systemctl(1), clone(2), getrlimit(2), kill(2), ptrace(2), rt_sigqueueinfo(2), sigaction(2), signal(2), signalfd(2), sigprocmask(2), sigwaitinfo(2), id_t(3type), psignal(3), pthread_sigqueue(3), sigevent(3type), org.freedesktop.systemd1(5), credentials(7), signal(7)

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