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exit(2)								      exit(2)



NAME

  exit,	atexit,	_exit -	Terminates a process

LIBRARY

  Standard C Library (libc)

SYNOPSIS

  #include <&lt;stdlib.h>&gt;

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

  void exit(
	  int status);

  #include <&lt;unistd.h>&gt;

  void _exit(
	  int status);

STANDARDS

  Interfaces documented	on this	reference page conform to industry standards
  as follows:

  exit(), _exit(), atexit(): XSH4.2

  Refer	to the standards(5) reference page for more information	about indus-
  try standards	and associated tags.

PARAMETERS

  status    Indicates the status of the	process.

  function  Points to a	function that is called	at normal process termination
	    for	cleanup	processing.  The number	of exit	handlers that can be
	    specified with the atexit()	function is limited by the amount of
	    available virtual memory.

DESCRIPTION

  The atexit() function	registers functions to be called at normal process
  termination for cleanup processing.  The function adds a single exit
  handler to a list of handlers	to be called at	process	termination.  The
  system calls the functions in	reverse	order, calling the function at the
  top of the list first.  Any function that is registered more than once will
  be repeated.

  The exit() function terminates the calling process after calling the
  _cleanup() function to flush any buffered output.  Then it calls any
  functions registered previously for the process by the atexit() function,
  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 termination and does
  not return.

  The _exit() and exit() functions terminate the calling process and cause
  the following	to occur:

    +  All of the file descriptors and directory streams open in the calling
       process are closed.  Since the exit() function terminates the process,
       any errors encountered during these close operations go unreported.
       Message catalog descriptors and conversion descriptors opened in	the
       calling process are also	closed with no reporting of errors.

    +  The parent process ID of	all the	calling	process' existing child
       processes and zombie processes is reset.	 The child processes continue
       executing; however, their parent	process	ID is set to the process ID
       of init.	 The init process thus adopts each of these processes,
       catches the SIGCHLD signals that	they generate, and calls the wait()
       function	for each of them.

    +  If the parent process of	the calling process is running a wait()	or
       waitpid() function, that	parent process is notified that	the calling
       process is being	terminated. The	low-order 8 bits (that is, bits	0377
       or 0xFF)	of the status parameter	are made available to the parent pro-
       cess.

       [XSH4.2]	 This behavior also applies if the parent process is running
       a wait3() or waitid() function.	In addition, this behavior only
       applies when the	parent process of the calling process has neither set
       its SA_NOCLDWAIT	flag nor set SIGCHLD to	SIG_IGN.

    +  If the parent process is	not running a wait() or	waitpid() function
       when the	child process terminates, the parent process receives a
       SIGCHLD signal to notify	it that	the child process is terminating.
       The child process is transformed	into a zombie process.

       Once the	parent process calls the wait()	or waitpid() routine, the
       child process completes termination and the low-order 8 bits (that is,
       bits 0377 or 0xFF) of the status	parameter are made available to	it.

       [XSH4.2]	 This behavior also applies to the wait3() and waitid()	func-
       tions.  In addition, this behavior only applies when the	parent pro-
       cess has	not set	its SA_NOCLDWAIT flag or set SIGCHLD to	SIG_IGN.

    +  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 the process is a controlling process,	the system sends a SIGHUP
       signal to each process executing	in the foreground on the terminal
       that belongs to the calling process.  The terminal is disassociated
       from the	session, allowing it to	be acquired by a new controlling pro-
       cess.

    +  If the termination of a process causes a	process	group to become
       orphaned, and if	any member of the newly	orphaned process group is
       stopped,	a SIGHUP signal, followed by a SIGCONT signal, is sent to
       each newly orphaned process.

    +  [XSH4.2]	  If the parent	process	has set	its SA_NOCLDWAIT flag or set
       SIGCHLD to SIG_IGN, the status is discarded, and	the lifetime of	the
       calling process ends immediately.

    +  [XSH4.2]	 Each mapped memory object is unmapped.

    +  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. (For more information about the data
       structure, see shmget(2).)

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

    +  [Tru64 UNIX]  If	the process has	a process lock,	text lock, or data
       lock, an	unlock is performed. (See the plock() function.)

    +  [Tru64 UNIX]  An	accounting record is written to	the accounting file
       if the system accounting	routine	is enabled. (The acct()	function pro-
       vides information about enabling	accounting routines.)

    +  [Tru64 UNIX]  Locks set by the fcntl(), flock(),	and lockf() functions
       are removed.

  [Tru64 UNIX]	If a thread calls the _exit() function,	the entire process
  exits	and all	threads	within the process are terminated.

NOTES

  [XSH4.2]  An application should call sysconf() to obtain the value of
  {ATEXIT_MAX},	the number of handlers that can	be registered. There is	no
  way for an application to tell how many functions have already been
  registered with atexit().

  To prematurely terminate atexit handler processing from within a handler,
  _exit() can be called. It is not recommended to call exit() from within an
  atexit handler.

RETURN VALUES

  The exit() function and _exit() function do not return.

  The atexit() function	returns	0 (zero) if successful.	The function fails if
  an application attempts to register more process cleanup functions than
  available virtual memory allows.  In this case, the function returns a
  nonzero value.

RELATED	INFORMATION

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

  Standards: standards(5)