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

       │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

   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 5.06 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

Linux                             2017-09-15                       SIGQUEUE(3)