1SIGQUEUE(3)                Linux Programmer's Manual               SIGQUEUE(3)
2
3
4

NAME

6       sigqueue - queue a signal and data to a process
7

SYNOPSIS

9       #include <signal.h>
10
11       int sigqueue(pid_t pid, int sig, const union sigval value);
12
13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       sigqueue(): _POSIX_C_SOURCE >= 199309L
16

DESCRIPTION

18       sigqueue()  sends  the signal specified in sig to the process whose PID
19       is given in pid.  The permissions required to send  a  signal  are  the
20       same  as for kill(2).  As with kill(2), the null signal (0) can be used
21       to check if a process with a given PID exists.
22
23       The value argument is used to specify  an  accompanying  item  of  data
24       (either  an integer or a pointer value) to be sent with the signal, and
25       has the following type:
26
27           union sigval {
28               int   sival_int;
29               void *sival_ptr;
30           };
31
32       If the receiving process has installed a handler for this signal  using
33       the  SA_SIGINFO  flag to sigaction(2), then it can obtain this data via
34       the si_value field of the siginfo_t  structure  passed  as  the  second
35       argument to the handler.  Furthermore, the si_code field of that struc‐
36       ture will be set to SI_QUEUE.
37

RETURN VALUE

39       On success, sigqueue() returns 0, indicating that the signal  was  suc‐
40       cessfully  queued  to the receiving process.  Otherwise, -1 is returned
41       and errno is set to indicate the error.
42

ERRORS

44       EAGAIN The limit of signals which may be queued has been reached.  (See
45              signal(7) for further information.)
46
47       EINVAL sig was invalid.
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49       EPERM  The  process  does not have permission to send the signal to the
50              receiving process.  For the required permissions, see kill(2).
51
52       ESRCH  No process has a PID matching pid.
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VERSIONS

55       sigqueue() and  the  underlying  rt_sigqueueinfo()  system  call  first
56       appeared in Linux 2.2.
57

ATTRIBUTES

59       For   an   explanation   of   the  terms  used  in  this  section,  see
60       attributes(7).
61
62       ┌───────────┬───────────────┬─────────┐
63Interface  Attribute     Value   
64       ├───────────┼───────────────┼─────────┤
65sigqueue() │ Thread safety │ MT-Safe │
66       └───────────┴───────────────┴─────────┘

CONFORMING TO

68       POSIX.1-2001, POSIX.1-2008.
69

NOTES

71       If this function results in the sending of a signal to the process that
72       invoked  it, and that signal was not blocked by the calling thread, and
73       no other threads were willing to handle this signal (either  by  having
74       it  unblocked,  or  by  waiting for it using sigwait(3)), then at least
75       some signal must be delivered  to  this  thread  before  this  function
76       returns.
77
78   C library/kernel differences
79       On Linux, sigqueue() is implemented using the rt_sigqueueinfo(2) system
80       call.  The system call differs in its third argument, which is the sig‐
81       info_t  structure that will be supplied to the receiving process's sig‐
82       nal handler or returned  by  the  receiving  process's  sigtimedwait(2)
83       call.   Inside  the  glibc sigqueue() wrapper, this argument, uinfo, is
84       initialized as follows:
85
86           uinfo.si_signo = sig;      /* Argument supplied to sigqueue() */
87           uinfo.si_code = SI_QUEUE;
88           uinfo.si_pid = getpid();   /* Process ID of sender */
89           uinfo.si_uid = getuid();   /* Real UID of sender */
90           uinfo.si_value = val;      /* Argument supplied to sigqueue() */
91

SEE ALSO

93       kill(2),       rt_sigqueueinfo(2),       sigaction(2),       signal(2),
94       pthread_sigqueue(3), sigwait(3), signal(7)
95

COLOPHON

97       This  page  is  part of release 4.16 of the Linux man-pages project.  A
98       description of the project, information about reporting bugs,  and  the
99       latest     version     of     this    page,    can    be    found    at
100       https://www.kernel.org/doc/man-pages/.
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104Linux                             2017-09-15                       SIGQUEUE(3)
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