250 lines
6.3 KiB
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250 lines
6.3 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of ATEXIT</TITLE>
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</HEAD><BODY>
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<H1>ATEXIT</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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atexit - register a function to be called at normal process termination
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>></B>
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<B>int atexit(void (*</B><I>function</I><B>)(void));</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>atexit</B>()
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function registers the given
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<I>function</I>
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to be
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called at normal process termination, either via
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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3)
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or via return from the program's
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<I>main</I>().
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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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<P>
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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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<P>
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POSIX.1 requires that an implementation allow at least
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<B>ATEXIT_MAX</B>
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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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<B><A HREF="/cgi-bin/man/man2html?3+sysconf">sysconf</A></B>(3).
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<P>
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When a child process is created via
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(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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<B><A HREF="/cgi-bin/man/man2html?3+exec">exec</A></B>(3)
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functions,
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all registrations are removed.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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The
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<B>atexit</B>()
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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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<A NAME="lbAF"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>atexit</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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<P>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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Functions registered using
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<B>atexit</B>()
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(and
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<B><A HREF="/cgi-bin/man/man2html?3+on_exit">on_exit</A></B>(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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<P>
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If one of the registered functions calls
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<B><A HREF="/cgi-bin/man/man2html?2+_exit">_exit</A></B>(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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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3)
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are not performed.
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<P>
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POSIX.1 says that the result of calling
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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3)
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more than once (i.e., calling
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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3)
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within a function registered using
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<B>atexit</B>())
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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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portable programs should not invoke
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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3)
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inside a function registered using
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<B>atexit</B>().
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<P>
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The
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<B>atexit</B>()
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and
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<B><A HREF="/cgi-bin/man/man2html?3+on_exit">on_exit</A></B>(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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<P>
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According to POSIX.1, the result is undefined if
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<B><A HREF="/cgi-bin/man/man2html?3+longjmp">longjmp</A></B>(3)
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is used to terminate execution of one of the functions registered using
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<B>atexit</B>().
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<A NAME="lbAI"> </A>
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<H3>Linux notes</H3>
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Since glibc 2.2.3,
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<B>atexit</B>()
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(and
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<B><A HREF="/cgi-bin/man/man2html?3+on_exit">on_exit</A></B>(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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<A NAME="lbAJ"> </A>
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<H2>EXAMPLE</H2>
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#include <<A HREF="file:///usr/include/stdio.h">stdio.h</A>>
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#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>>
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#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>>
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<P>
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void
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bye(void)
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{
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<BR> printf("That was all, folks\n");
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}
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<P>
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int
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main(void)
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{
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<BR> long a;
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<BR> int i;
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<P>
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<BR> a = sysconf(_SC_ATEXIT_MAX);
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<BR> printf("ATEXIT_MAX = %ld\n", a);
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<P>
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<BR> i = atexit(bye);
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<BR> if (i != 0) {
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<BR> fprintf(stderr, "cannot set exit function\n");
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<BR> exit(EXIT_FAILURE);
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<BR> }
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<P>
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<BR> exit(EXIT_SUCCESS);
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}
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+_exit">_exit</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+dlopen">dlopen</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+exit">exit</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+on_exit">on_exit</A></B>(3)
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<A NAME="lbAL"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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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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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="5"><A HREF="#lbAF">ATTRIBUTES</A><DD>
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<DT id="6"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="7"><A HREF="#lbAH">NOTES</A><DD>
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<DL>
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<DT id="8"><A HREF="#lbAI">Linux notes</A><DD>
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</DL>
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<DT id="9"><A HREF="#lbAJ">EXAMPLE</A><DD>
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<DT id="10"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="11"><A HREF="#lbAL">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:36 GMT, March 31, 2021
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