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<h4 class="subsection">25.6.5 Termination Internals</h4>

<p>The <code>_exit</code> function is the primitive used for process termination
by <code>exit</code>.  It is declared in the header file <samp><span class="file">unistd.h</span></samp>. 
<a name="index-unistd_002eh-3144"></a>
<!-- unistd.h -->
<!-- POSIX.1 -->

<div class="defun">
&mdash; Function: void <b>_exit</b> (<var>int status</var>)<var><a name="index-g_t_005fexit-3145"></a></var><br>
<blockquote><p>The <code>_exit</code> function is the primitive for causing a process to
terminate with status <var>status</var>.  Calling this function does not
execute cleanup functions registered with <code>atexit</code> or
<code>on_exit</code>. 
</p></blockquote></div>

<!-- stdlib.h -->
<!-- ISO -->
<div class="defun">
&mdash; Function: void <b>_Exit</b> (<var>int status</var>)<var><a name="index-g_t_005fExit-3146"></a></var><br>
<blockquote><p>The <code>_Exit</code> function is the ISO&nbsp;C<!-- /@w --> equivalent to <code>_exit</code>. 
The ISO&nbsp;C<!-- /@w --> committee members were not sure whether the definitions of
<code>_exit</code> and <code>_Exit</code> were compatible so they have not used the
POSIX name.

        <p>This function was introduced in ISO&nbsp;C99<!-- /@w --> and is declared in
<samp><span class="file">stdlib.h</span></samp>. 
</p></blockquote></div>

   <p>When a process terminates for any reason&mdash;either because the program
terminates, or as a result of a signal&mdash;the
following things happen:

     <ul>
<li>All open file descriptors in the process are closed.  See <a href="Low_002dLevel-I_002fO.html#Low_002dLevel-I_002fO">Low-Level I/O</a>. 
Note that streams are not flushed automatically when the process
terminates; see <a href="I_002fO-on-Streams.html#I_002fO-on-Streams">I/O on Streams</a>.

     <li>A process exit status is saved to be reported back to the parent process
via <code>wait</code> or <code>waitpid</code>; see <a href="Process-Completion.html#Process-Completion">Process Completion</a>.  If the
program exited, this status includes as its low-order 8 bits the program
exit status.

     <li>Any child processes of the process being terminated are assigned a new
parent process.  (On most systems, including GNU, this is the <code>init</code>
process, with process ID 1.)

     <li>A <code>SIGCHLD</code> signal is sent to the parent process.

     <li>If the process is a session leader that has a controlling terminal, then
a <code>SIGHUP</code> signal is sent to each process in the foreground job,
and the controlling terminal is disassociated from that session. 
See <a href="Job-Control.html#Job-Control">Job Control</a>.

     <li>If termination of a process causes a process group to become orphaned,
and any member of that process group is stopped, then a <code>SIGHUP</code>
signal and a <code>SIGCONT</code> signal are sent to each process in the
group.  See <a href="Job-Control.html#Job-Control">Job Control</a>. 
</ul>

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