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; 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
     information 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 has terminated, status
     identifies the cause of termination and passes useful
     information 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 (that is, 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).

STATUS MESSAGES AND VALUES
     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



January 1992                                                    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
     calling process.  Otherwise, a value of -1 is returned and
     errno is set to indicate the error.

     The wait program 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.

WARNINGS
     See WARNINGS in signal(3).

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





































2                                                    January 1992