sigqueue(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

SIGQUEUE(3)             Linux Programmer's Manual            SIGQUEUE(3)

NAME         top

       sigqueue - queue a signal and data to a process

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.

VERSIONS         top

       sigqueue() and the underlying rt_sigqueueinfo() system call first
       appeared in Linux 2.2.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             Attribute     Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │sigqueue()                            │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

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.

   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() */

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 release 5.11 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                          2021-03-22                    SIGQUEUE(3)

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