262 lines
6.6 KiB
HTML
262 lines
6.6 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PTHREAD_ATTR_SETGUARDSIZE</TITLE>
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</HEAD><BODY>
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<H1>PTHREAD_ATTR_SETGUARDSIZE</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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pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard size
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attribute in thread attributes object
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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/pthread.h">pthread.h</A>></B>
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<B>int pthread_attr_setguardsize(pthread_attr_t *</B><I>attr</I><B>, size_t </B><I>guardsize</I><B>);</B>
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<B>int pthread_attr_getguardsize(const pthread_attr_t *</B><I>attr</I><B>, size_t *</B><I>guardsize</I><B>);</B>
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Compile and link with <I>-pthread</I>.
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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>pthread_attr_setguardsize</B>()
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function sets the guard size attribute of the
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thread attributes object referred to by
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<I>attr</I>
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to the value specified in
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<I>guardsize</I>.
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<P>
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If
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<I>guardsize</I>
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is greater than 0,
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then for each new thread created using
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<I>attr</I>
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the system allocates an additional region of at least
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<I>guardsize</I>
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bytes at the end of the thread's stack to act as the guard area
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for the stack (but see BUGS).
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<P>
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If
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<I>guardsize</I>
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is 0, then new threads created with
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<I>attr</I>
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will not have a guard area.
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<P>
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The default guard size is the same as the system page size.
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<P>
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If the stack address attribute has been set in
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<I>attr</I>
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(using
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_attr_setstack">pthread_attr_setstack</A></B>(3)
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or
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_attr_setstackaddr">pthread_attr_setstackaddr</A></B>(3)),
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meaning that the caller is allocating the thread's stack,
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then the guard size attribute is ignored
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(i.e., no guard area is created by the system):
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it is the application's responsibility to handle stack overflow
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(perhaps by using
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<B><A HREF="/cgi-bin/man/man2html?2+mprotect">mprotect</A></B>(2)
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to manually define a guard area at the end of the stack
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that it has allocated).
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<P>
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The
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<B>pthread_attr_getguardsize</B>()
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function returns the guard size attribute of the
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thread attributes object referred to by
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<I>attr</I>
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in the buffer pointed to by
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<I>guardsize</I>.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, these functions return 0;
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on error, they return a nonzero error number.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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POSIX.1 documents an
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<B>EINVAL</B>
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error if
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<I>attr</I>
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or
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<I>guardsize</I>
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is invalid.
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On Linux these functions always succeed
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(but portable and future-proof applications should nevertheless
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handle a possible error return).
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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These functions are provided by glibc since version 2.1.
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<A NAME="lbAH"> </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>pthread_attr_setguardsize</B>(),
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<B>pthread_attr_getguardsize</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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<A NAME="lbAI"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008.
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<A NAME="lbAJ"> </A>
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<H2>NOTES</H2>
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A guard area consists of virtual memory pages that are protected
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to prevent read and write access.
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If a thread overflows its stack into the guard area,
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then, on most hard architectures, it receives a
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<B>SIGSEGV</B>
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signal, thus notifying it of the overflow.
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Guard areas start on page boundaries,
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and the guard size is internally rounded up to
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the system page size when creating a thread.
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(Nevertheless,
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<B>pthread_attr_getguardsize</B>()
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returns the guard size that was set by
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<B>pthread_attr_setguardsize</B>().)
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<P>
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Setting a guard size of 0 may be useful to save memory
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in an application that creates many threads
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and knows that stack overflow can never occur.
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<P>
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Choosing a guard size larger than the default size
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may be necessary for detecting stack overflows
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if a thread allocates large data structures on the stack.
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<A NAME="lbAK"> </A>
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<H2>BUGS</H2>
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As at glibc 2.8, the NPTL threading implementation includes
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the guard area within the stack size allocation,
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rather than allocating extra space at the end of the stack,
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as POSIX.1 requires.
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(This can result in an
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<B>EINVAL</B>
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error from
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_create">pthread_create</A></B>(3)
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if the guard size value is too large,
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leaving no space for the actual stack.)
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<P>
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The obsolete LinuxThreads implementation did the right thing,
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allocating extra space at the end of the stack for the guard area.
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<A NAME="lbAL"> </A>
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<H2>EXAMPLE</H2>
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See
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_getattr_np">pthread_getattr_np</A></B>(3).
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<A NAME="lbAM"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+mprotect">mprotect</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_attr_init">pthread_attr_init</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_attr_setstack">pthread_attr_setstack</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_attr_setstacksize">pthread_attr_setstacksize</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_create">pthread_create</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+pthreads">pthreads</A></B>(7)
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<A NAME="lbAN"> </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">ERRORS</A><DD>
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<DT id="6"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="7"><A HREF="#lbAH">ATTRIBUTES</A><DD>
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<DT id="8"><A HREF="#lbAI">CONFORMING TO</A><DD>
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<DT id="9"><A HREF="#lbAJ">NOTES</A><DD>
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<DT id="10"><A HREF="#lbAK">BUGS</A><DD>
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<DT id="11"><A HREF="#lbAL">EXAMPLE</A><DD>
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<DT id="12"><A HREF="#lbAM">SEE ALSO</A><DD>
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<DT id="13"><A HREF="#lbAN">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: 00:05:53 GMT, March 31, 2021
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