Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
WAIT(2)			    BSD	System Calls Manual		       WAIT(2)

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

     Standard C	Library	(libc, -lc)

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

     wait(int *status);

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

     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 *rusage);

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

     The wpid parameter	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	parameter is defined below.  The options parameter contains
     the bitwise OR of any of the following options.  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 processes).

     When the WNOHANG option is	specified and no processes wish	to report sta-
     tus, 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	non-zero
     (true) value:

	     True if the process terminated normally by	a call to _exit(2) or

	     True if the process terminated due	to receipt of a	signal.

	     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:

	     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.

	     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 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 re-

	     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	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 intro(2), System
     call restart.

     If	wait() returns due to a	stopped	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	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 or exited children,	0 is returned.	If an error is de-
     tected 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 unwaited-for child

     [EFAULT]		The status or rusage arguments point to	an illegal ad-
			dress.	(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.

     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-

     ptrace(2),	sigaction(2), _exit(2),	exit(3)

     A wait() function call appeared in	Version	6 AT&T UNIX.

BSD				April 19, 1994				   BSD


Want to link to this manual page? Use this URL:

home | help