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WAIT(2)			  FreeBSD System Calls Manual		       WAIT(2)

NAME
     wait, waitpid, wait4, wait3 -- wait for process termination

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/wait.h>

     pid_t
     wait(int *status);

     #include <sys/time.h>
     #include <sys/resource.h>

     pid_t
     waitpid(pid_t wpid, int *status, int options);

     pid_t
     wait3(int *status,	int options, struct rusage *rusage);

     pid_t
     wait4(pid_t wpid, int *status, int	options, struct	rusage *rusage);

DESCRIPTION
     The wait()	function suspends execution of its calling process until
     status information	is available for a terminated child process, or	a sig-
     nal is received.  On return from a	successful wait() call,	the status
     area contains termination information about the process that exited as
     defined below.

     The wait4() system	call provides a	more general interface for programs
     that need to wait for certain child processes, that need resource uti-
     lization statistics accumulated by	child processes, or that require
     options.  The other wait functions	are implemented	using wait4().

     The wpid argument specifies the set of child processes for	which to wait.
     If	wpid is	-1, the	call waits for any child process.  If wpid is 0, the
     call waits	for any	child process in the process group of the caller.  If
     wpid is greater than zero,	the call 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 absolute value	of wpid.

     The status	argument is defined below.  The	options	argument contains the
     bitwise OR	of any of the following	options.  The WCONTINUED option	indi-
     cates that	children of the	current	process	that have continued from a job
     control stop, by receiving	a SIGCONT signal, should also have their sta-
     tus reported.  The	WNOHANG	option is used to indicate that	the call
     should not	block if there are no processes	that wish to report status.
     If	the WUNTRACED option is	set, children of the current process that are
     stopped due 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 the terminated
     process and all its children is returned (this information	is currently
     not available for stopped or continued processes).

     When the WNOHANG option is	specified and no processes wish	to report sta-
     tus, wait4() returns a process id of 0.

     The waitpid() function 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	non-zero
     (true) value:

     WIFCONTINUED(status)
	     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).

     WIFEXITED(status)
	     True if the process terminated normally by	a call to _exit(2) or
	     exit(3).

     WIFSIGNALED(status)
	     True if the process terminated due	to receipt of a	signal.

     WIFSTOPPED(status)
	     True if the process has not terminated, but has stopped and can
	     be	restarted.  This macro can be true only	if the wait call spec-
	     ified the WUNTRACED option	or if the child	process	is being
	     traced (see ptrace(2)).

     Depending on the values of	those macros, the following macros produce the
     remaining status information about	the child process:

     WEXITSTATUS(status)
	     If	WIFEXITED(status) is true, evaluates to	the low-order 8	bits
	     of	the argument passed to _exit(2)	or exit(3) by the child.

     WTERMSIG(status)
	     If	WIFSIGNALED(status) is true, evaluates to the number of	the
	     signal that caused	the termination	of the process.

     WCOREDUMP(status)
	     If	WIFSIGNALED(status) is true, evaluates as true if the termina-
	     tion of the process was accompanied by the	creation of a core
	     file containing an	image of the process when the signal was
	     received.

     WSTOPSIG(status)
	     If	WIFSTOPPED(status) is true, evaluates to the number of the
	     signal that caused	the process to stop.

NOTES
     See sigaction(2) for a list of termination	signals.  A status of 0	indi-
     cates normal termination.

     If	a parent process terminates without waiting for	all of its child pro-
     cesses to terminate, the remaining	child processes	are assigned the par-
     ent process 1 ID (the init	process	ID).

     If	a signal is caught while any of	the wait() calls are pending, the call
     may be interrupted	or restarted when the signal-catching routine returns,
     depending on the options in effect	for the	signal;	see discussion of
     SA_RESTART	in sigaction(2).

     The implementation	queues one SIGCHLD signal for each child process whose
     status has	changed, if wait() returns because the status of a child
     process is	available, the pending SIGCHLD signal associated with the
     process ID	of the child process will be discarded.	 Any other pending
     SIGCHLD signals remain pending.

     If	SIGCHLD	is blocked, wait() returns because the status of a child
     process is	available, the pending SIGCHLD signal will be cleared unless
     another status of the child process is available.

RETURN VALUES
     If	wait() returns due to a	stopped, continued, or terminated child
     process, the process ID of	the child is returned to the calling process.
     Otherwise,	a value	of -1 is returned and errno is set to indicate the
     error.

     If	wait4(), wait3(), or waitpid() returns due to a	stopped, continued, or
     terminated	child process, the process ID of the child is returned to the
     calling 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, continued 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.

ERRORS
     The wait()	function will fail and return immediately if:

     [ECHILD]		The calling process has	no existing unwaited-for child
			processes.

     [ECHILD]		No status from the terminated child process is avail-
			able because the calling process has asked the system
			to discard such	status by ignoring the signal SIGCHLD
			or setting the flag SA_NOCLDWAIT for that signal.

     [EFAULT]		The status or rusage argument points to	an illegal
			address.  (May not be detected before exit of a	child
			process.)

     [EINTR]		The call was interrupted by a caught signal, or	the
			signal did not have the	SA_RESTART flag	set.

SEE ALSO
     _exit(2), ptrace(2), sigaction(2),	exit(3), siginfo(3)

STANDARDS
     The wait()	and waitpid() functions	are defined by POSIX; wait4() and
     wait3() are not specified by POSIX.  The WCOREDUMP() macro	and the	abil-
     ity to restart a pending wait() call are extensions to the	POSIX inter-
     face.

HISTORY
     The wait()	function appeared in Version 6 AT&T UNIX.

FreeBSD	9.3		       November	12, 2005		   FreeBSD 9.3

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY

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