281 lines
6.0 KiB
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281 lines
6.0 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 REMAP_FILE_PAGES</TITLE>
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</HEAD><BODY>
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<H1>REMAP_FILE_PAGES</H1>
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Section: Linux Programmer's Manual (2)<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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remap_file_pages - create a nonlinear file mapping
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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>#define _GNU_SOURCE</B> /* See <A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A>(7) */
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<B>#include <<A HREF="file:///usr/include/sys/mman.h">sys/mman.h</A>></B>
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<B>int remap_file_pages(void *</B><I>addr</I><B>, size_t </B><I>size</I><B>, int </B><I>prot</I><B>,</B>
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<B> size_t </B><I>pgoff</I><B>, int </B><I>flags</I><B>);</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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<B>Note</B>:
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this system call was marked as deprecated starting with Linux 3.16.
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In Linux 4.0, the implementation was replaced
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by a slower in-kernel emulation.
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Those few applications that use this system call should
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consider migrating to alternatives.
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This change was made because the kernel code for this system call was complex,
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and it is believed to be little used or perhaps even completely unused.
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While it had some use cases in database applications on 32-bit systems,
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those use cases don't exist on 64-bit systems.
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<P>
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The
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<B>remap_file_pages</B>()
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system call is used to create a nonlinear mapping, that is, a mapping
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in which the pages of the file are mapped into a nonsequential order
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in memory.
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The advantage of using
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<B>remap_file_pages</B>()
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over using repeated calls to
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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is that the former approach does not require the kernel to create
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additional VMA (Virtual Memory Area) data structures.
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<P>
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To create a nonlinear mapping we perform the following steps:
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<DL COMPACT>
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<DT id="1">1.<DD>
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Use
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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to create a mapping (which is initially linear).
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This mapping must be created with the
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<B>MAP_SHARED</B>
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flag.
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<DT id="2">2.<DD>
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Use one or more calls to
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<B>remap_file_pages</B>()
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to rearrange the correspondence between the pages of the mapping
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and the pages of the file.
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It is possible to map the same page of a file
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into multiple locations within the mapped region.
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</DL>
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<P>
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The
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<I>pgoff</I>
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and
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<I>size</I>
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arguments specify the region of the file that is to be relocated
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within the mapping:
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<I>pgoff</I>
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is a file offset in units of the system page size;
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<I>size</I>
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is the length of the region in bytes.
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<P>
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The
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<I>addr</I>
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argument serves two purposes.
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First, it identifies the mapping whose pages we want to rearrange.
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Thus,
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<I>addr</I>
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must be an address that falls within
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a region previously mapped by a call to
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2).
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Second,
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<I>addr</I>
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specifies the address at which the file pages
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identified by
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<I>pgoff</I>
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and
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<I>size</I>
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will be placed.
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<P>
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The values specified in
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<I>addr</I>
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and
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<I>size</I>
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should be multiples of the system page size.
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If they are not, then the kernel rounds
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<I>both</I>
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values
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<I>down</I>
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to the nearest multiple of the page size.
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<P>
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The
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<I>prot</I>
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argument must be specified as 0.
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<P>
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The
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<I>flags</I>
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argument has the same meaning as for
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2),
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but all flags other than
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<B>MAP_NONBLOCK</B>
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are ignored.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>remap_file_pages</B>()
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returns 0.
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On error, -1 is returned, and
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<I>errno</I>
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is set appropriately.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="3"><B>EINVAL</B>
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<DD>
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<I>addr</I>
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does not refer to a valid mapping
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created with the
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<B>MAP_SHARED</B>
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flag.
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<DT id="4"><B>EINVAL</B>
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<DD>
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<I>addr</I>,
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<I>size</I>,
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<I>prot</I>,
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or
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<I>pgoff</I>
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is invalid.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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The
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<B>remap_file_pages</B>()
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system call appeared in Linux 2.5.46;
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glibc support was added in version 2.3.3.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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The
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<B>remap_file_pages</B>()
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system call is Linux-specific.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Since Linux 2.6.23,
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<B>remap_file_pages</B>()
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creates non-linear mappings only
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on in-memory filesystems such as
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<B><A HREF="/cgi-bin/man/man2html?5+tmpfs">tmpfs</A></B>(5),
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hugetlbfs or ramfs.
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On filesystems with a backing store,
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<B>remap_file_pages</B>()
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is not much more efficient than using
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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to adjust which parts of the file are mapped to which addresses.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+getpagesize">getpagesize</A></B>(2),
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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+mmap2">mmap2</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?2+mremap">mremap</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+msync">msync</A></B>(2)
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<A NAME="lbAK"> </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="5"><A HREF="#lbAB">NAME</A><DD>
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<DT id="6"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="7"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="8"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="9"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="10"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="11"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="12"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="13"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="14"><A HREF="#lbAK">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: 00:05:34 GMT, March 31, 2021
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