WAIT(2) 							System Calls 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 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
       statistics accummulated 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 cur-
       rently 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 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(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 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 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 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 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 call-
       ing process.  If there are no children not previously awaited, -1 is returned with errno set to [ECHILD].  Otherwise, if WNOHANG is  speci-
       fied 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 extensions to the POSIX interface.

SEE ALSO

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

4th Berkeley Distribution					  March 12, 1993							   WAIT(2)