wait, waitpid, wait4, wait3 - wait for process termination
waitpid(pid_t wpid, int *status, int options);
wait3(int *status, int options, struct rusage *rusage);
wait4(pid_t wpid, int *status, int options, struct rusage
The wait() function suspends execution of its calling process until
status information is available for a terminated child process, or a signal
is received. On return from a successful wait() call,
area, if non-zero, is filled in with termination information
process that exited (see below).
The wait4() call provides a more general interface for programs that need
to wait for certain child processes, that need resource utilization
statistics accumulated by child processes, or that require
other wait functions are implemented using wait4().
The wpid parameter specifies the set of child processes for
wait. The following symbolic constants are currently defined in
#define WAIT_ANY (-1) /* any process */
#define WAIT_MYPGRP 0 /* any process in my
process group */
If wpid is set to WAIT_ANY, the call waits for any child
wpid is set to WAIT_MYPGRP, the call waits for any child
process in the
process group of the caller. If wpid is greater than zero,
waits for the process with process ID wpid. If wpid is less
than -1, the
call waits for any process whose process group ID equals the
value of wpid.
The status parameter is defined below. The options parameter contains
the bitwise OR of any of the following options:
WCONTINUED Causes status to be reported for stopped child
have been continued by receipt of a SIGCONT signal.
WNOHANG Indicates that the call should not block if
there are no processes
that wish to report status.
WUNTRACED If set, children of the current process that are
to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal also have
their status reported.
If rusage is non-zero, a summary of the resources used by
process and all its children is returned (this information
not available for stopped processes).
When the WNOHANG option is specified and no processes wish
to report status,
wait4() returns a process ID of 0.
The waitpid() call is identical to wait4() with an rusage
value of zero.
The older wait3() call is the same as wait4() with a wpid
value of -1.
The following macros may be used to test the manner of exit
of the process.
One of the first three macros will evaluate to a nonzero (true)
True if the process has not terminated, and has continued after a
job control stop. This macro can be true only if
the wait call
specified the WCONTINUED option).
True if the process terminated normally by a call to
True if the process terminated due to receipt of a
True if the process has not terminated, but has
stopped and can
be restarted. This macro can be true only if the
wait call specified
the WUNTRACED option or if the child process
traced (see ptrace(2)).
Depending on the values of those macros, the following
macros produce the
remaining status information about the child process:
If WIFEXITED(status) is true, evaluates to the loworder 8 bits
of the argument passed to _exit(2) or exit(3) by the
If WIFSIGNALED(status) is true, evaluates to the
number of the
signal that caused the termination of the process.
If WIFSIGNALED(status) is true, evaluates as true if
of the process was accompanied by the creation
of a core
file containing an image of the process when the
signal was received.
If WIFSTOPPED(status) is true, evaluates to the number of the
signal that caused the process to stop.
See sigaction(2) for a list of termination signals. A status of 0 indicates
If a parent process terminates without waiting for all of
its child processes
to terminate, the remaining child processes are assigned the parent
process 1 ID (the init process ID).
If a signal is caught while any of the wait() calls is pending, the call
may be interrupted or restarted when the signal-catching
depending on the options in effect for the signal; for further information,
If wait() returns due to a stopped or terminated child process, the process
ID of the child is returned to the calling process.
value of -1 is returned and errno is set to indicate the error.
If wait4(), wait3() or waitpid() returns due to a stopped or
child process, the process ID of the child is returned to
process. If there are no children not previously awaited,
-1 is returned
with errno set to [ECHILD]. Otherwise, if WNOHANG is specified and there
are no stopped or exited children, 0 is returned. If an error is detected
or a caught signal aborts the call, a value of -1 is returned and
errno is set to indicate the error.
wait() will fail and return immediately if:
[ECHILD] The calling process has no existing unwaitedfor child processes.
[EFAULT] The status or rusage arguments point to an illegal address.
(May not be detected before exit of a child
[EINTR] The call was interrupted by a caught signal,
or the signal
did not have the SA_RESTART flag set.
[EINVAL] Invalid or undefined flags were passed in the
_exit(2), sigaction(2), exit(3)
The wait() and waitpid() functions are defined by POSIX;
wait3() are not specified by POSIX. The WCOREDUMP() macro
and the ability
to restart a pending wait() call are extensions to the
A wait() function call appeared in Version 2 AT&T UNIX.
OpenBSD 3.6 April 19, 1994
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