waitpid(2)                                                       waitpid(2)


   NAME
         waitpid - wait for child process to change state

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

         pid_t waitpid (pid_t pid, int *stat_loc, 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 (pid_t)-1, status is requested for any child
               process.

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

               If pid is equal to (pid_t)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 (pid_t)-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)                                                       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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