NAME
	  exit,	atexit,	_exit -	Terminates a process

     LIBRARY
	  Standard C Library (libc.a): atexit(), _exit()

     SYNOPSIS
	  #include <stdlib.h>

	  void exit (
		  int status );

	  void _exit (
		  int status );

	  int atexit (
		  void	(*function) ( void ) );

     PARAMETERS
	  status    Indicates the status of the	process.

	  function  Points to a	function that is called	at normal pro-
		    cess termination for cleanup processing. A push-
		    down stack of functions is kept, such that the
		    last function registered is	the first function
		    called.  Any function which	is registered more
		    than once will be repeated.	 Up to 32 functions
		    can	be specified with atexit().

     DESCRIPTION
	  The atexit() function	registers functions to be called at
	  normal process termination for cleanup processing.

	  The exit() function terminates the calling process after
	  calling the Standard I/O Library _cleanup() function to
	  flush	any buffered output.  Then it calls any	functions
	  registered previously	for the	process	by the atexit()	func-
	  tion,	in the reverse order to	that in	which they were
	  registered. In addition, the exit() function flushes all
	  open output streams, closes all open streams,	and removes
	  all files created by the tmpfile() function.	Finally, it
	  calls	the _exit() function, which completes process termina-
	  tion and does	not return.

	  The _exit() function terminates the calling process and
	  causes the following to occur:

	  o    All of the file descriptors, directory streams, and
	       message catalog descriptors open	in the calling process
	       are closed. Since the exit() function terminates	the
	       process,	any errors encountered during these close
	       operations go unreported.

	  o    Terminating a process by	exiting	does not terminate its
	       child processes.	 Instead, the parent process ID	of all
	       of the calling process child processes and zombie child
	       processes is set	to the process ID of init.  The	init
	       process thus inherits each of these processes, catches
	       the SIGCHLD signals they	generate, and calls the	wait()
	       function	for each of them.

	  o    If the parent process of	the calling process is running
	       a wait()	or waitpid() function, it is notified of the
	       termination of the calling process and the low-order 8
	       bits (that is, bits 0377	or 0xFF) of the	status parame-
	       ter are made available to it.

	  o    If the parent process is	not running a wait() or
	       waitpid() function when the child process terminates,
	       it may do so later on, and the child's status will be
	       returned	to it at that time.  Meanwhile,	the child pro-
	       cess is transformed into	a zombie process, and its
	       parent process is sent a	SIGCHLD	signal to notify it of
	       the termination of a child process.
	       A zombie	process	is a process that occupies a slot in
	       the process table, but has no other space allocated to
	       it either in user or kernel space. The process table
	       slot that it occupies is	partially overlaid with	time
	       accounting information to be used by the	times()	func-
	       tion. (See the sys/proc.h header	file.)
	       A process remains a zombie until	its parent issues one
	       of the wait functions. At this time, the	zombie is laid
	       to rest,	and its	process	table entry is released.

	  o    The parent process is sent a SIGCHLD signal when	a
	       child terminates; however, since	the default action for
	       this signal is to ignore	it, the	signal usually is not
	       seen.
	       If an exiting child's parent is ignoring	the SIGCHLD
	       signal, the child's parent process ID is	changed	to
	       that of the initialization process, init, which will
	       catch the SIGCHLD signal	and call the wait() function.

	  o    If the process is a controlling process,	a SIGHUP sig-
	       nal is sent to each process in the foreground process
	       group of	the controlling	terminal belonging to the cal-
	       ling process.  The controlling terminal is disassoci-
	       ated from the session, allowing it to be	acquired by a
	       new controlling process.

	  o    If the exit of a	process	causes a process group to
	       become orphaned,	and if any member of the newly
	       orphaned	process	group is stopped, then a SIGHUP	signal
	       is sent to each newly orphaned process.

	  o    Each attached shared memory segment is detached and the
	       value of	shm_nattach in the data	structure associated
	       with its	shared memory identifier is decremented	by 1.

	  o    For each	semaphore for which the	calling	process	has
	       set a semadj value, that	semadj value is	added to the
	       semval of the specified semaphore. (The semop() func-
	       tion provides information about semaphore operations.)

	  o    If the process has a process lock, text lock, or	data
	       lock, an	unlock is performed. (See the plock() func-
	       tion.)

	  o    An accounting record is written on the accounting file
	       if the system accounting	routine	is enabled. (The
	       acct() function provides	information about enabling
	       accounting routines.)

	  o    Locks set by the	fcntl(), flock(),and lockf() functions
	       are removed.

	  If a thread calls the	_exit()	function, the entire process
	  exits	and all	threads	within the process are terminated.

     NOTES
	  The system init process is used to assist cleanup of ter-
	  minating processes. If the code for the init process is
	  replaced, the	program	must be	prepared to accept SIGCHLD
	  signals and issue a wait() function for each.

	  AES Support Level: Full use

     RETURN VALUES
	  The exit() function and _exit() function do not return.  The
	  atexit() function returns 0 (zero) if	successful, and	a
	  nonzero value	if there has been an attempt to	register more
	  exit() functions than	can be held in the atexit() array.

     RELATED INFORMATION
	  Functions: acct(2), sigaction(2), times(3), wait(2),
	  sigvec(2)