NAME

       sigqueue — queue a signal to a process (REALTIME)

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <signal.h>

       int
       sigqueue(pid_t pid, int signo, const union sigval value);

DESCRIPTION

       The  sigqueue()  system  call causes the signal specified by signo to be sent with the value specified by
       value to the process specified by pid.  If signo is zero (the null signal), error checking  is  performed
       but no signal is actually sent.  The null signal can be used to check the validity of PID.

       The  conditions  required  for  a process to have permission to queue a signal to another process are the
       same as for the kill(2) system call.  The sigqueue() system call queues a  signal  to  a  single  process
       specified by the pid argument.

       The sigqueue() system call returns immediately.  If the resources were available to queue the signal, the
       signal will be queued and sent to the receiving process.

       If the value of pid causes signo to be generated for the sending process, and if signo is not blocked for
       the  calling  thread  and if no other thread has signo unblocked or is waiting in a sigwait() system call
       for signo, either signo or at least the pending, unblocked signal will be delivered to the calling thread
       before sigqueue() returns.  Should any multiple pending signals in the  range  SIGRTMIN  to  SIGRTMAX  be
       selected  for  delivery,  it  is  the lowest numbered one.  The selection order between realtime and non-
       realtime signals, or between multiple pending non-realtime signals, is unspecified.

RETURN VALUES

       Upon successful completion, the value 0 is returned; otherwise the value -1 is returned  and  the  global
       variable errno is set to indicate the error.

ERRORS

       The sigqueue() system call will fail if:

       [EAGAIN]           No  resources  are  available  to  queue  the  signal.  The process has already queued
                          {SIGQUEUE_MAX} signals that are still pending at the  receiver(s),  or  a  system-wide
                          resource limit has been exceeded.

       [EINVAL]           The value of the signo argument is an invalid or unsupported signal number.

       [EPERM]            The  process  does  not  have  the  appropriate  privilege  to  send the signal to the
                          receiving process.

       [ESRCH]            The process pid does not exist.

SEE ALSO

       kill(2),  sigaction(2),  sigpending(2),  sigsuspend(2),  sigtimedwait(2),   sigwait(2),   sigwaitinfo(2),
       pause(3), pthread_sigmask(3), siginfo(3)

STANDARDS

       The sigqueue() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

HISTORY

       Support for POSIX realtime signal queue first appeared in FreeBSD 7.0.

CAVEATS

       When  using  sigqueue to send signals to a process which might have a different ABI (for instance, one is
       32-bit and the other 64-bit), the sival_int member of value can be delivered reliably, but the  sival_ptr
       may  be  truncated  in  endian dependent ways and must not be relied on.  Further, many pointer integrity
       schemes disallow sending pointers to other processes, and this technique should not be used  in  programs
       intended to be portable.

Debian                                             May 5, 2017                                       SIGQUEUE(2)