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wait4(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 processes).
     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 intro(2), System
     call restart.

RETURN VALUES

     If wait() returns due to a stopped or terminated child process, the
     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.

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.

SEE ALSO

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

HISTORY

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

FreeBSD 5.4			April 19, 1994			   FreeBSD 5.4

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