on_exit - register a function to be called at normal process termination


#include <stdlib.h>

int on_exit(void (*function)(int , void *), void *arg);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

on_exit(): Since glibc 2.19: _DEFAULT_SOURCE Glibc 2.19 and earlier: _BSD_SOURCE || _SVID_SOURCE


The on_exit() function registers the given function to be called at normal process termination, whether via exit(3) or via return from the program's main(). The function is passed the status argument given to the last call to exit(3) and the arg argument from on_exit().

The same function may be registered multiple times: it is called once for each registration.

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 on_exit() 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
on_exit() Thread safety MT-Safe


This function comes from SunOS 4, but is also present in glibc. It no longer occurs in Solaris (SunOS 5). Portable application should avoid this function, and use the standard atexit(3) instead.


By the time function is executed, stack (auto) variables may already have gone out of scope. Therefore, arg should not be a pointer to a stack variable; it may however be a pointer to a heap variable or a global variable.


_exit(2), atexit(3), exit(3)


This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at