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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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atexit(3) Library Functions Manual atexit(3)
atexit - register a function to be called at normal process
termination
Standard C library (libc, -lc)
#include <stdlib.h>
int atexit(typeof(void (void)) *function);
The atexit() function registers the given function to be called at
normal process termination, either via exit(3) or via return from
the program's main(). Functions so registered are called in the
reverse order of their registration; no arguments are passed.
The same function may be registered multiple times: it is called
once for each registration.
POSIX.1 requires that an implementation allow at least ATEXIT_MAX
(32) such functions to be registered. The actual limit supported
by an implementation can be obtained using sysconf(3).
When a child process is created via fork(2), it inherits copies of
its parent's registrations. Upon a successful call to one of the
exec(3) functions, all registrations are removed.
The atexit() function returns the value 0 if successful; otherwise
it returns a nonzero value.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ atexit() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1 says that the result of calling exit(3) more than once
(i.e., calling exit(3) within a function registered using
atexit()) is undefined. On some systems (but not Linux), this can
result in an infinite recursion; portable programs should not
invoke exit(3) inside a function registered using atexit().
C11, POSIX.1-2008.
POSIX.1-2001, C89, C99, SVr4, 4.3BSD.
Functions registered using atexit() (and on_exit(3)) are not
called if a process terminates abnormally because of the delivery
of a signal.
If one of the registered functions calls _exit(2), then any
remaining functions are not invoked, and the other process
termination steps performed by exit(3) are not performed.
The atexit() and on_exit(3) functions register functions on the
same list: at normal process termination, the registered functions
are invoked in reverse order of their registration by these two
functions.
According to POSIX.1, the result is undefined if longjmp(3) is
used to terminate execution of one of the functions registered
using atexit().
Linux notes
Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a
shared library to establish functions that are called when the
shared library is unloaded.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static void
bye(void)
{
printf("That was all, folks\n");
}
int
main(void)
{
long a;
int i;
a = sysconf(_SC_ATEXIT_MAX);
printf("ATEXIT_MAX = %ld\n", a);
i = atexit(bye);
if (i != 0) {
fprintf(stderr, "cannot set exit function\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
_exit(2), dlopen(3), exit(3), on_exit(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 atexit(3)
Pages that refer to this page: execve(2), _exit(2), abort(3), dlopen(3), exit(3), on_exit(3), pmdaopenlog(3), pmfault(3), pmopenlog(3), pthread_atfork(3), pthread_exit(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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