1WAIT(2) Linux Programmer's Manual WAIT(2)
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6 wait, waitpid, waitid - wait for process to change state
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9 #include <sys/types.h>
10 #include <sys/wait.h>
11 pid_t wait(int *wstatus);
13 pid_t waitpid(pid_t pid, int *wstatus, int options);
15 int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
17 /* This is the glibc and POSIX interface; see
18 NOTES for information on the raw system call. */
19 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
21 waitid():
23 Since glibc 2.26: _XOPEN_SOURCE >= 500 ||
24 _POSIX_C_SOURCE >= 200809L
25 Glibc 2.25 and earlier:
26 _XOPEN_SOURCE
27 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
28 || /* Glibc versions <= 2.19: */ _BSD_SOURCE
29
31 All of these system calls are used to wait for state changes in a child
32 of the calling process, and obtain information about the child whose
33 state has changed. A state change is considered to be: the child ter‐
34 minated; the child was stopped by a signal; or the child was resumed by
35 a signal. In the case of a terminated child, performing a wait allows
36 the system to release the resources associated with the child; if a
37 wait is not performed, then the terminated child remains in a "zombie"
38 state (see NOTES below).
39 If a child has already changed state, then these calls return immedi‐
41 ately. Otherwise, they block until either a child changes state or a
42 signal handler interrupts the call (assuming that system calls are not
43 automatically restarted using the SA_RESTART flag of sigaction(2)). In
44 the remainder of this page, a child whose state has changed and which
45 has not yet been waited upon by one of these system calls is termed
46 waitable.
47 wait() and waitpid()
49 The wait() system call suspends execution of the calling thread until
50 one of its children terminates. The call wait(&wstatus) is equivalent
51 to:
52 waitpid(-1, &wstatus, 0);
54 The waitpid() system call suspends execution of the calling thread
56 until a child specified by pid argument has changed state. By default,
57 waitpid() waits only for terminated children, but this behavior is mod‐
58 ifiable via the options argument, as described below.
59 The value of pid can be:
61 < -1 meaning wait for any child process whose process group ID is
63 equal to the absolute value of pid.
64 -1 meaning wait for any child process.
66 0 meaning wait for any child process whose process group ID is
68 equal to that of the calling process.
69 > 0 meaning wait for the child whose process ID is equal to the
71 value of pid.
72 The value of options is an OR of zero or more of the following