285 lines
6.6 KiB
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285 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 GETSOCKOPT</TITLE>
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</HEAD><BODY>
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<H1>GETSOCKOPT</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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getsockopt, setsockopt - get and set options on sockets
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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/sys/types.h">sys/types.h</A>></B> /* See NOTES */
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<B>#include <<A HREF="file:///usr/include/sys/socket.h">sys/socket.h</A>></B>
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<B>int getsockopt(int </B><I>sockfd</I><B>, int </B><I>level</I><B>, int </B><I>optname</I><B>,</B>
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<B> void *</B><I>optval</I><B>, socklen_t *</B><I>optlen</I><B>);</B>
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<B>int setsockopt(int </B><I>sockfd</I><B>, int </B><I>level</I><B>, int </B><I>optname</I><B>,</B>
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<B> const void *</B><I>optval</I><B>, socklen_t </B><I>optlen</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>getsockopt</B>()
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and
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<B>setsockopt</B>()
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manipulate options for the socket referred to by the file descriptor
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<I>sockfd</I>.
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Options may exist at multiple
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protocol levels; they are always present at the uppermost
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socket level.
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<P>
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When manipulating socket options, the level at which the
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option resides and the name of the option must be specified.
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To manipulate options at the sockets API level,
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<I>level</I>
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is specified as
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<B>SOL_SOCKET</B>.
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To manipulate options at any
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other level the protocol number of the appropriate protocol
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controlling the option is supplied.
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For example,
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to indicate that an option is to be interpreted by the
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<B>TCP</B>
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protocol,
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<I>level</I>
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should be set to the protocol number of
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<B>TCP</B>;
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see
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<B><A HREF="/cgi-bin/man/man2html?3+getprotoent">getprotoent</A></B>(3).
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<P>
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The arguments
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<I>optval</I>
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and
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<I>optlen</I>
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are used to access option values for
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<B>setsockopt</B>().
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For
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<B>getsockopt</B>()
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they identify a buffer in which the value for the
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requested option(s) are to be returned.
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For
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<B>getsockopt</B>(),
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<I>optlen</I>
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is a value-result argument, initially containing the
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size of the buffer pointed to by
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<I>optval</I>,
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and modified on return to indicate the actual size of
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the value returned.
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If no option value is to be supplied or returned,
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<I>optval</I>
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may be NULL.
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<P>
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<I>Optname</I>
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and any specified options are passed uninterpreted to the appropriate
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protocol module for interpretation.
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The include file
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<I><<A HREF="file:///usr/include/sys/socket.h">sys/socket.h</A>></I>
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contains definitions for socket level options, described below.
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Options at
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other protocol levels vary in format and name; consult the appropriate
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entries in section 4 of the manual.
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<P>
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Most socket-level options utilize an
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<I>int</I>
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argument for
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<I>optval</I>.
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For
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<B>setsockopt</B>(),
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the argument should be nonzero to enable a boolean option, or zero if the
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option is to be disabled.
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<P>
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For a description of the available socket options see
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<B><A HREF="/cgi-bin/man/man2html?7+socket">socket</A></B>(7)
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and the appropriate protocol man pages.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, zero is returned for the standard options.
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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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<P>
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Netfilter allows the programmer
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to define custom socket options with associated handlers; for such
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options, the return value on success is the value returned by the handler.
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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="1"><B>EBADF</B>
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<DD>
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The argument
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<I>sockfd</I>
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is not a valid file descriptor.
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<DT id="2"><B>EFAULT</B>
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<DD>
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The address pointed to by
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<I>optval</I>
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is not in a valid part of the process address space.
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For
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<B>getsockopt</B>(),
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this error may also be returned if
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<I>optlen</I>
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is not in a valid part of the process address space.
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<DT id="3"><B>EINVAL</B>
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<DD>
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<I>optlen</I>
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invalid in
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<B>setsockopt</B>().
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In some cases this error can also occur for an invalid value in
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<I>optval</I>
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(e.g., for the
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<B>IP_ADD_MEMBERSHIP</B>
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option described in
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<B><A HREF="/cgi-bin/man/man2html?7+ip">ip</A></B>(7)).
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<DT id="4"><B>ENOPROTOOPT</B>
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<DD>
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The option is unknown at the level indicated.
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<DT id="5"><B>ENOTSOCK</B>
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<DD>
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The file descriptor
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<I>sockfd</I>
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does not refer to a socket.
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</DL>
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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,
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SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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POSIX.1 does not require the inclusion of
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<I><<A HREF="file:///usr/include/sys/types.h">sys/types.h</A>></I>,
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and this header file is not required on Linux.
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However, some historical (BSD) implementations required this header
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file, and portable applications are probably wise to include it.
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<P>
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For background on the
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<I>socklen_t</I>
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type, see
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<B><A HREF="/cgi-bin/man/man2html?2+accept">accept</A></B>(2).
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<A NAME="lbAI"> </A>
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<H2>BUGS</H2>
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Several of the socket options should be handled at lower levels of the
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system.
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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+ioctl">ioctl</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+socket">socket</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+getprotoent">getprotoent</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?5+protocols">protocols</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?7+ip">ip</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+packet">packet</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+socket">socket</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+tcp">tcp</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+udp">udp</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+unix">unix</A></B>(7)
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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="6"><A HREF="#lbAB">NAME</A><DD>
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<DT id="7"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="8"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="9"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="10"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="11"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="12"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="13"><A HREF="#lbAI">BUGS</A><DD>
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<DT id="14"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="15"><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: 00:05:32 GMT, March 31, 2021
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</BODY>
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</HTML>
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