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

NAME
       wait3, wait4 - wait for process termination, BSD style

SYNOPSIS
       #define _USE_BSD
       #include <sys/types.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 pro-
       cess until a child has exited, or until a signal is deliv-
       ered  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 "zom-
       bie" process), the function returns immediately.  Any sys-
       tem resources used by the child are freed.

       The  wait4 function suspends execution of the current pro-
       cess 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"  pro-
       cess),  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 infor-
       mation 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 argument to a  call
               to  exit()  or as the argument for a return state-
               ment in the main program.  This macro can only  be
               evaluated if WIFEXITED 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.

       ERESTARTSYS
              if WNOHANG was not set and an unblocked signal or a
              SIGCHLD  was  caught. This error is returned by the
              system call.  The library interface is not  allowed
              to return ERESTARTSYS, but will return EINTR.

CONFORMING TO
       SVr4, POSIX.1

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

Linux                      23 June 1997                         1