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WAIT(2) 		       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 signal is re-
     ceived.  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 utilization
     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  op-
     tions.   The  WCONTINUED  option  indicates  that	children  of the current
     process that have continued from a job control stop, by receiving a SIGCONT
     signal, should also have their status 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.  The WSTOPPED option is an
     alias for WUNTRACED.  The WNOWAIT option keeps the process whose status  is
     returned  in  a  waitable state.  The process may be waited for again after
     this call completes.

     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  specified
	     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 sig-
	     nal 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  sig-
	     nal 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
     processes 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 re-
     main 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  re-
     turned 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 available
			because the calling process has asked the system to dis-
			card such status by ignoring the signal SIGCHLD or  set-
			ting the flag SA_NOCLDWAIT for that signal.

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

     [EINTR]		The call was interrupted by a caught signal, or the sig-
			nal 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  ability
     to restart a pending wait() call are extensions to the POSIX interface.

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

FreeBSD 7.1			November 12, 2005			 WAIT(2)
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