WAIT(2)             UNIX Programmer's Manual		  WAIT(2)


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

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

     pid = wait(status)
     int pid;
     union wait *status;

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

     pid = waitpid(wpid, status, options);
     int pid;
     int wpid;
     union wait *status;
     int options;

     pid = wait3(status, options, rusage);
     int pid;
     union wait *status;
     int options;
     struct rusage *rusage;

     pid = wait4(wpid, status, options, rusage);
     int pid;
     int wpid;
     union wait *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 received.	On return from a success-
     ful wait call, the status area contains termination informa-
     tion about the process that exited as defined below.

     The wait4 call provides a more general interface for pro-
     grams that need to wait for certain child processes, that
     need resource utilization statistics accummulated by child
     processes, or that require options.  The other wait func-
     tions 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


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WAIT(2)             UNIX Programmer's Manual		  WAIT(2)


     whose process group id equals the absolute value of wpid .

     The status parameter is defined below.  The options parame-
     ter 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 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 non-zero (true) value:

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

     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 mac-
     ros produce the remaining status information about the child
     process:

     WEXITSTATUS(status) - If WIFEXITED(status) is true, evalu-
     ates to the low-order 8 bits of the argument passed to
     _exit(2) or exit(2) 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 termination of the process was accompanied by


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WAIT(2)             UNIX Programmer's Manual		  WAIT(2)


     the creation of a core file containing an image of the pro-
     cess 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 sigvec(2) for a list of termination signals.  A status
     of 0 indicates normal termination.

     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 pend-
     ing, 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 pro-
     cess, 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 detected or a caught signal aborts the call, a value of
     -1 is returned and errno is set to indicate the error.

ERRORS
     Wait() will fail and return immediately if:

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

     [EFAULT]	    The status or rusage arguments point 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 had the SV_INTERRUPT 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 ability to restart a pending wait call are


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WAIT(2)             UNIX Programmer's Manual		  WAIT(2)


     extensions to the POSIX interface.

SEE ALSO
     exit(2) , sigvec(2) A wait function call appeared in Version
     6 AT&T UNIX.


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