sigqueue(3) - Linux manual page (original) (raw)

sigqueue(3) Library Functions Manual sigqueue(3)

NAME top

   sigqueue - queue a signal and data to a process

LIBRARY top

   Standard C library (_libc_, _-lc_)

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)](../man2/kill.2.html).  As with [kill(2)](../man2/kill.2.html), 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)](../man2/sigaction.2.html), then it can obtain this
   data via the _sivalue_ field of the _siginfot_ structure passed as
   the second argument to the handler.  Furthermore, the _sicode_
   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](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **EAGAIN** The limit of signals which may be queued has been reached.
          (See [signal(7)](../man7/signal.7.html) 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)](../man2/kill.2.html).

   **ESRCH** No process has a PID matching _pid_.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **sigqueue**()                           │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

VERSIONS top

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 siginfot 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() */

STANDARDS top

   POSIX.1-2008.

HISTORY top

   Linux 2.2.  POSIX.1-2001.

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)](../man3/sigwait.3.html)), then at least some signal must be delivered to this
   thread before this function returns.

COLOPHON top

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   man-pages@man7.org

Linux man-pages 6.10 2024-07-23 sigqueue(3)

Pages that refer to this page:kill(1), kill(1@@procps-ng), pgrep(1), systemctl(1), clone(2), getrlimit(2), kill(2), ptrace(2), rt_sigqueueinfo(2), sigaction(2), signal(2), signalfd(2), sigprocmask(2), sigwaitinfo(2), id_t(3type), psignal(3), pthread_sigqueue(3), sigevent(3type), org.freedesktop.systemd1(5), credentials(7), signal(7)