WAIT(2)              INTERACTIVE UNIX System              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
               The wait system call 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 is non-zero, 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 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 (i.e., bit 200) is set, a ``core image''
                    will have been produced [see signal(2)].

               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)].

               The wait system call will fail and return immediately if one
               or more of the following is true:

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



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          WAIT(2)              INTERACTIVE UNIX System              WAIT(2)



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

          DIAGNOSTICS
               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
               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.












































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          WARNING
               The wait system call fails and its actions are undefined if
               stat_loc points to an invalid address.




















































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