WAIT4(2)						     Linux Programmer's Manual							  WAIT4(2)

NAME

       wait3, wait4 - wait for process termination, BSD style

SYNOPSIS

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

       pid_t wait3(int *status, int options,
	     struct rusage *rusage);

       pid_t wait4(pid_t pid, int *status, int options,
	     struct rusage *rusage);

DESCRIPTION

       The  wait3  function  suspends execution of the current process until a child has exited, or until a signal is delivered whose action is to
       terminate the current process or to call a signal handling function.  If a child has already exited by the time of the  call  (a  so-called
       "zombie" process), the function returns immediately.  Any system resources used by the child are freed.

       The  wait4  function suspends execution of the current process until a child as specified by the pid argument has exited, or until a signal
       is delivered whose action is to terminate the current process or to call a signal handling function.  If a child as requested  by  pid  has
       already	exited by the time of the call (a so-called "zombie" process), the function returns immediately.  Any system resources used by the
       child are freed.

       The value of pid can be one of:

       < -1   which means to wait for any child process whose process group ID is equal to the absolute value of pid.

       -1     which means to wait for any child process; this is equivalent to calling wait3.

       0      which means to wait for any child process whose process group ID is equal to that of the calling process.

       > 0    which means to wait for the child whose process ID is equal to the value of pid.

       The value of options is a bitwise OR of zero or more of the following constants:

       WNOHANG
	      which means to return immediately if no child is there to be waited for.

       WUNTRACED
	      which means to also return for children which are stopped, and whose status has not been reported.

       If status is not NULL, wait3 or wait4 store status information in the location pointed to by status.

       This status can be evaluated with the following macros (these macros take the stat buffer (an int) as an argument -- not a pointer  to  the
       buffer!):

       WIFEXITED(status)
	      is non-zero if the child exited normally.

       WEXITSTATUS(status)
	      evaluates to the least significant eight bits of the return code of the child which terminated, which may have been set as the argu-
	      ment to a call to exit() or as the argument for a return statement in the main program.  This macro can only be evaluated if  WIFEX-
	      ITED returned non-zero.

       WIFSIGNALED(status)
	      returns true if the child process exited because of a signal which was not caught.

       WTERMSIG(status)
	      returns  the  number  of	the  signal  that  caused  the child process to terminate. This macro can only be evaluated if WIFSIGNALED
	      returned non-zero.

       WIFSTOPPED(status)
	      returns true if the child process which caused the return is currently stopped; this is only possible if the  call  was  done  using
	      WUNTRACED.

       WSTOPSIG(status)
	      returns the number of the signal which caused the child to stop.	This macro can only be evaluated if WIFSTOPPED returned non-zero.

       If  rusage  is  not  NULL,  the	struct rusage as defined in <sys/resource.h> it points to will be filled with accounting information.  See
       getrusage(2) for details.

RETURN VALUE

       The process ID of the child which exited, -1 on error (in particular, when no unwaited-for child processes of the specified kind exist)	or
       zero if WNOHANG was used and no child was available yet.  In the latter two cases errno will be set appropriately.

ERRORS

       ECHILD No unwaited-for child process as specified does exist.

       EINTR  if WNOHANG was not set and an unblocked signal or a SIGCHLD was caught.

NOTES

       Including  <sys/time.h> is not required these days, but increases portability.  (Indeed, <sys/resource.h> defines the rusage structure with
       fields of type struct timeval defined in <sys/time.h>.)

       The prototype for these functions is only available  if	_BSD_SOURCE  is  defined  (either  explicitly,	or  implicitly,  by  not  defining
       _POSIX_SOURCE or compiling with the -ansi flag).

CONFORMING TO

       SVr4, POSIX.1

SEE ALSO

       signal(2), getrusage(2), wait(2), signal(7)

Linux								    1997-06-23								  WAIT4(2)