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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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sigqueue(3) Library Functions Manual sigqueue(3)
sigqueue - queue a signal and data to a process
Standard C library (libc, -lc)
#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
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.
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.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ sigqueue() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
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() */
POSIX.1-2008.
Linux 2.2. POSIX.1-2001.
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.
kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
pthread_sigqueue(3), sigwait(3), signal(7)
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-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. 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 6.15 2025-05-17 sigqueue(3)
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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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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