1SIGQUEUE(3) Linux Programmer's Manual SIGQUEUE(3)
2
6 sigqueue - queue a signal and data to a process
7
9 #include <signal.h>
10 int sigqueue(pid_t pid, int sig, const union sigval value);
12 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
14 sigqueue():
16 _POSIX_C_SOURCE >= 199309L
17
19 sigqueue() sends the signal specified in sig to the process whose PID
20 is given in pid. The permissions required to send a signal are the
21 same as for kill(2). As with kill(2), the null signal (0) can be used
22 to check if a process with a given PID exists.
23 The value argument is used to specify an accompanying item of data (ei‐
25 ther an integer or a pointer value) to be sent with the signal, and has
26 the following type:
27 union sigval {
29 int sival_int;
30 void *sival_ptr;
31 };
32 If the receiving process has installed a handler for this signal using
34 the SA_SIGINFO flag to sigaction(2), then it can obtain this data via
35 the si_value field of the siginfo_t structure passed as the second ar‐
36 gument to the handler. Furthermore, the si_code field of that struc‐
37 ture will be set to SI_QUEUE.
38
40 On success, sigqueue() returns 0, indicating that the signal was suc‐
41 cessfully queued to the receiving process. Otherwise, -1 is returned
42 and errno is set to indicate the error.
43
45 EAGAIN The limit of signals which may be queued has been reached. (See
46 signal(7) for further information.)
47 EINVAL sig was invalid.
49 EPERM The process does not have permission to send the signal to the
51 receiving process. For the required permissions, see kill(2).
52 ESRCH No process has a PID matching pid.
54
56 sigqueue() and the underlying rt_sigqueueinfo(2) system call first ap‐
57 peared in Linux 2.2.
58
60 For an explanation of the terms used in this section, see at‐
61 tributes(7).
62 ┌────────────────────────────────────────────┬───────────────┬─────────┐
64 │Interface │ Attribute │ Value │
65 ├────────────────────────────────────────────┼───────────────┼─────────┤
66 │sigqueue() │ Thread safety │ MT-Safe │
67 └────────────────────────────────────────────┴───────────────┴─────────┘
68
70 POSIX.1-2001, POSIX.1-2008.
71
73 If this function results in the sending of a signal to the process that
74 invoked it, and that signal was not blocked by the calling thread, and
75 no other threads were willing to handle this signal (either by having
76 it unblocked, or by waiting for it using sigwait(3)), then at least
77 some signal must be delivered to this thread before this function re‐
78 turns.
79 C library/kernel differences
81 On Linux, sigqueue() is implemented using the rt_sigqueueinfo(2) system
82 call. The system call differs in its third argument, which is the sig‐
83 info_t structure that will be supplied to the receiving process's sig‐
84 nal handler or returned by the receiving process's sigtimedwait(2)
85 call. Inside the glibc sigqueue() wrapper, this argument, uinfo, is
86 initialized as follows:
87 uinfo.si_signo = sig; /* Argument supplied to sigqueue() */
89 uinfo.si_code = SI_QUEUE;
90 uinfo.si_pid = getpid(); /* Process ID of sender */
91 uinfo.si_uid = getuid(); /* Real UID of sender */
92 uinfo.si_value = val; /* Argument supplied to sigqueue() */
93
95 kill(2), rt_sigqueueinfo(2), sigaction(2), signal(2),
96 pthread_sigqueue(3), sigwait(3), signal(7)
97
99 This page is part of release 5.13 of the Linux man-pages project. A
100 description of the project, information about reporting bugs, and the
101 latest version of this page, can be found at
102 https://www.kernel.org/doc/man-pages/.
103Linux 2021-03-22 SIGQUEUE(3)