sigqueue(3) Library Functions Manual sigqueue(3)
NAME
sigqueue - queue a signal and data to a process
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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
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 (ei-
ther 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 ar-
gument to the handler. Furthermore, the si_code field of that struc-
ture will be set to SI_QUEUE.
RETURN VALUE
On success, sigqueue() returns 0, indicating that the signal was suc-
cessfully queued to the receiving process. Otherwise, -1 is returned
and errno is set to indicate the error.
ERRORS
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.
VERSIONS
sigqueue() and the underlying rt_sigqueueinfo(2) system call first ap-
peared in Linux 2.2.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│sigqueue() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2001, POSIX.1-2008.
NOTES
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 re-
turns.
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 sig-
info_t structure that will be supplied to the receiving process's sig-
nal 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() */
SEE ALSO
kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
pthread_sigqueue(3), sigwait(3), signal(7)
Linux man-pages 6.03 2022-12-15 sigqueue(3)
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