BSD 2.11 - man page for wait4 (bsd section 2)

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WAIT(2) 										  WAIT(2)

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

       #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;

       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  suc-
       cessful 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  cer-
       tain child processes, that need resource utilization statistics accummulated by child pro-
       cesses, 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 pro-

       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.

       See sigvec(2) for a list of termination signals.  A status of 0 indicates normal  termina-

       If  a  parent  process terminates without waiting for all of its child processes to termi-
       nate, the remaining child processes are assigned the parent process 1 ID (the init process

       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.

       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
       detected 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 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.

       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.

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

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