wait(2)                                                   wait(2)



     NAME
          wait - wait for child process to stop or terminate

     SYNOPSIS
          int wait(stat_loc)
          int *stat_loc;

          int wait((int*)0)

     DESCRIPTION
          wait suspends the calling process until one of the immediate
          children terminates or until a child that is being traced
          stops, because it has hit a break point.  The wait system
          call will return prematurely if a signal is received and if
          a child process stopped or terminated prior to the call on
          wait, return is immediate.

          If stat_loc (taken as an integer) is nonzero, 16 bits of in-
          formation called status are stored in the low order 16 bits
          of the location pointed to by stat_loc.  status can be used
          to differentiate between stopped and terminated child
          processes and if the child process terminated, status iden-
          tifies the cause of termination and passes useful informa-
          tion to the parent.  This is accomplished in the following
          manner:

               If the child process stopped, the high order 8 bits of
               status will contain the number of the signal that
               caused the process to stop and the low order 8 bits
               will be set equal to 0177.

               If the child process terminated due to an exit call,
               the low order 8 bits of status will be zero and the
               high order 8 bits will contain the low order 8 bits of
               the argument that the child process passed to exit; see
               exit(2).

               If the child process terminated due to a signal, the
               high order 8 bits of status will be zero and the low
               order 8 bits will contain the number of the signal that
               caused the termination. In addition, if the low order
               seventh bit (i.e., bit 200) is set, a ``core image''
               will have been produced; see signal(3).

          If a parent process terminates without waiting for its child
          processes to terminate, the parent process ID of each child
          process is set to 1. This means the initialization process
          inherits the child processes; see intro(2).

     RETURN VALUE
          If wait returns due to the receipt of a signal, a value of
          -1 is returned to the calling process and errno is set to



     April, 1990                                                     1

     wait(2)                                                   wait(2)



          EINTR.  If wait returns due to a stopped or terminated child
          process, the process ID of the child is returned to the cal-
          ling process.  Otherwise, a value of -1 is returned and
          errno is set to indicate the error.

     ERRORS
          wait will fail and return immediately if one or more of the
          following are true:

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

     SEE ALSO
          exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2),
          wait3(2N), signal(3).

     WARNINGS
          See WARNINGS in signal(3).





































     2                                                     April, 1990