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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified 1993-03-29, David Metcalfe
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.\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
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.\" Modified 2003-10-25, Walter Harms
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.\"
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.TH ATEXIT 3 2017-09-15 "Linux" "Linux Programmer's Manual"
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.SH NAME
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atexit \- register a function to be called at normal process termination
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.PP
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.BI "int atexit(void (*" function )(void));
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.fi
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.SH DESCRIPTION
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The
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.BR atexit ()
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function registers the given
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.I function
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to be
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called at normal process termination, either via
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.BR exit (3)
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or via return from the program's
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.IR main ().
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Functions so registered are called in
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the reverse order of their registration; no arguments are passed.
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.PP
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The same function may be registered multiple times:
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it is called once for each registration.
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.PP
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POSIX.1 requires that an implementation allow at least
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.\" POSIX.1-2001, POSIX.1-2008
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.B ATEXIT_MAX
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(32) such functions to be registered.
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The actual limit supported by an implementation can be obtained using
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.BR sysconf (3).
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.PP
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When a child process is created via
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.BR fork (2),
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it inherits copies of its parent's registrations.
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Upon a successful call to one of the
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.BR exec (3)
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functions,
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all registrations are removed.
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.SH RETURN VALUE
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The
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.BR atexit ()
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function returns the value 0 if successful; otherwise
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it returns a nonzero value.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR atexit ()
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T} Thread safety MT-Safe
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.TE
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.sp 1
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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.SH NOTES
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Functions registered using
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.BR atexit ()
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(and
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.BR on_exit (3))
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are not called if a process terminates abnormally because
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of the delivery of a signal.
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.PP
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If one of the functions registered functions calls
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.BR _exit (2),
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then any remaining functions are not invoked,
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and the other process termination steps performed by
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.BR exit (3)
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are not performed.
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.PP
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POSIX.1 says that the result of calling
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.\" POSIX.1-2001, POSIX.1-2008
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.BR exit (3)
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more than once (i.e., calling
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.BR exit (3)
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within a function registered using
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.BR atexit ())
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is undefined.
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On some systems (but not Linux), this can result in an infinite recursion;
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.\" This can happen on OpenBSD 4.2 for example, and is documented
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.\" as occurring on FreeBSD as well.
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.\" Glibc does "the Right Thing" -- invocation of the remaining
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.\" exit handlers carries on as normal.
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portable programs should not invoke
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.BR exit (3)
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inside a function registered using
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.BR atexit ().
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.PP
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The
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.BR atexit ()
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and
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.BR on_exit (3)
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functions register functions on the same list:
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at normal process termination,
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the registered functions are invoked in reverse order
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of their registration by these two functions.
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.PP
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According to POSIX.1, the result is undefined if
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.BR longjmp (3)
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is used to terminate execution of one of the functions registered using
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.BR atexit ().
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.\" In glibc, things seem to be handled okay
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.SS Linux notes
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Since glibc 2.2.3,
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.BR atexit ()
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(and
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.BR on_exit (3))
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can be used within a shared library to establish functions
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that are called when the shared library is unloaded.
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.SH EXAMPLE
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.EX
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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void
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bye(void)
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{
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printf("That was all, folks\en");
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}
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|
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int
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main(void)
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{
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long a;
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int i;
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|
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a = sysconf(_SC_ATEXIT_MAX);
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printf("ATEXIT_MAX = %ld\en", a);
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i = atexit(bye);
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if (i != 0) {
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fprintf(stderr, "cannot set exit function\en");
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exit(EXIT_FAILURE);
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}
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|
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
|
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.BR _exit (2),
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.BR dlopen (3),
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.BR exit (3),
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.BR on_exit (3)
|
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.SH COLOPHON
|
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This page is part of release 4.15 of the Linux
|
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.I man-pages
|
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project.
|
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A description of the project,
|
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information about reporting bugs,
|
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and the latest version of this page,
|
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can be found at
|
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\%https://www.kernel.org/doc/man\-pages/.
|