waitpid(2)                       UNIX System V                       waitpid(2)


NAME
      waitpid - wait for child process to change state

SYNOPSIS
      #include <sys/types.h>
      #include <sys/wait.h>

      pidt waitpid (pidt pid, int *statloc, int options);

DESCRIPTION
      waitpid suspends the calling process until one of its children changes
      state; if a child process changed state prior to the call to waitpid,
      return is immediate.  pid specifies a set of child processes for which
      status is requested.

            If pid is equal to (pidt)-1, status is requested for any child
            process.

            If pid is greater than (pidt)0, it specifies the process ID of the
            child process for which status is requested.

            If pid is equal to (pidt)0 status is requested for any child
            process whose process group ID is equal to that of the calling
            process.

            If pid is less than (pidt)-1, status is requested for any child
            process whose process group ID is equal to the absolute value of
            pid.

      If waitpid returns because the status of a child process is available,
      then that status may be evaluated with the macros defined by wstat(5) .
      If the calling process had specified a non-zero value of stat_loc, the
      status of the child process will be stored in the location pointed to by
      stat_loc.

      The options argument is constructed from the bitwise inclusive OR of zero
      or more of the following flags, defined in the header file <sys/wait.h>:

      WCONTINUED     the status of any continued child process specified by
                     pid, whose status has not been reported since it
                     continued, shall also be reported to the calling process.

      WNOHANG        waitpid will not suspend execution of the calling process
                     if status is not immediately available for one of the
                     child processes specified by pid.

      WNOWAIT        keep the process whose status is returned in stat_loc in a
                     waitable state. The process may be waited for again with
                     identical results.





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waitpid(2)                       UNIX System V                       waitpid(2)


      WUNTRACED      the status of any child processes specified by pid that
                     are stopped, and whose status has not yet been reported
                     since they stopped, shall also be reported to the calling
                     process.

      waitpid with options equal to WUNTRACED and pid equal to (pid_t)-1 is
      identical to a call to wait(2).

      waitpid will fail if one or more of the following is true:

      EINTR          waitpid was interrupted due to the receipt of a signal
                     sent by the calling process.

      EINVAL         An invalid value was specified for options.

      ECHILD         The process or process group specified by pid does not
                     exist or is not a child of the calling process or can
                     never be in the states specified by options.

SEE ALSO
      exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2), signal(2),
      sigaction(2), siginfo(5), wstat(5)

DIAGNOSTICS
      If waitpid returns because the status of a child process is available,
      this function shall return a value equal to the process ID of the child
      process for which status is reported.  If waitpid returns due to the
      delivery of a signal to the calling process, a value of -1 shall be
      returned and errno shall be set to EINTR.  If this function was invoked
      with WNOHANG set in options, it has at least one child process specified
      by pid for which status is not available, and status is not available for
      any process specified by pid, a value of 0 shall be returned.  Otherwise,
      a value of -1 shall be returned, and errno shall be set to indicate the
      error.




















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