# sigqueue

## 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
           (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



           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



           **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_.
    


## ATTRIBUTES



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


## VERSIONS



       **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() */
    


## STANDARDS



           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 returns.
    


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