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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SIGQUEUE(3) Linux Programmer's Manual SIGQUEUE(3)
sigqueue - queue a signal and data to a process
#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.
sigqueue() and the underlying rt_sigqueueinfo() system call first
appeared in Linux 2.2.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────┼───────────────┼─────────┤
│sigqueue() │ Thread safety │ MT-Safe │
└───────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008.
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.
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() */
kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
pthread_sigqueue(3), sigwait(3), signal(7)
This page is part of release 4.12 of the Linux 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/.
Linux 2015-07-23 SIGQUEUE(3)
Pages that refer to this page: kill(1), getrlimit(2), kill(2), ptrace(2), rt_sigqueueinfo(2), sigaction(2), signal(2), signalfd(2), sigprocmask(2), sigwaitinfo(2), psignal(3), pthread_sigqueue(3), credentials(7), signal(7), signal-safety(7)