284 lines
5.9 KiB
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284 lines
5.9 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 SEM_OPEN</TITLE>
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</HEAD><BODY>
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<H1>SEM_OPEN</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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sem_open - initialize and open a named semaphore
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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/fcntl.h">fcntl.h</A>></B> /* For O_* constants */
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<B>#include <<A HREF="file:///usr/include/sys/stat.h">sys/stat.h</A>></B> /* For mode constants */
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<B>#include <<A HREF="file:///usr/include/semaphore.h">semaphore.h</A>></B>
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<B>sem_t *sem_open(const char *</B><I>name</I><B>, int </B><I>oflag</I><B>);</B>
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<B>sem_t *sem_open(const char *</B><I>name</I><B>, int </B><I>oflag</I><B>, </B>
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<B> mode_t </B><I>mode</I><B>, unsigned int </B><I>value</I><B>);</B>
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</PRE>
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<P>
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Link with <I>-pthread</I>.
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>sem_open</B>()
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creates a new POSIX semaphore or opens an existing semaphore.
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The semaphore is identified by
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<I>name</I>.
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For details of the construction of
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<I>name</I>,
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see
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<B><A HREF="/cgi-bin/man/man2html?7+sem_overview">sem_overview</A></B>(7).
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<P>
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The
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<I>oflag</I>
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argument specifies flags that control the operation of the call.
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(Definitions of the flags values can be obtained by including
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<I><<A HREF="file:///usr/include/fcntl.h">fcntl.h</A>></I>.)
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If
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<B>O_CREAT</B>
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is specified in
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<I>oflag</I>,
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then the semaphore is created if
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it does not already exist.
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The owner (user ID) of the semaphore is set to the effective
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user ID of the calling process.
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The group ownership (group ID) is set to the effective group ID
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of the calling process.
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If both
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<B>O_CREAT</B>
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and
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<B>O_EXCL</B>
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are specified in
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<I>oflag</I>,
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then an error is returned if a semaphore with the given
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<I>name</I>
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already exists.
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<P>
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If
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<B>O_CREAT</B>
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is specified in
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<I>oflag</I>,
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then two additional arguments must be supplied.
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The
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<I>mode</I>
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argument specifies the permissions to be placed on the new semaphore,
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as for
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<B><A HREF="/cgi-bin/man/man2html?2+open">open</A></B>(2).
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(Symbolic definitions for the permissions bits can be obtained by including
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<I><<A HREF="file:///usr/include/sys/stat.h">sys/stat.h</A>></I>.)
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The permissions settings are masked against the process umask.
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Both read and write permission should be granted to each class of
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user that will access the semaphore.
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The
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<I>value</I>
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argument specifies the initial value for the new semaphore.
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If
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<B>O_CREAT</B>
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is specified, and a semaphore with the given
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<I>name</I>
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already exists, then
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<I>mode</I>
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and
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<I>value</I>
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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>sem_open</B>()
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returns the address of the new semaphore;
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this address is used when calling other semaphore-related functions.
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On error,
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<B>sem_open</B>()
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returns
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<B>SEM_FAILED</B>,
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with
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<I>errno</I>
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set to indicate the error.
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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>EACCES</B>
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<DD>
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The semaphore exists, but the caller does not have permission to
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open it.
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<DT id="2"><B>EEXIST</B>
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<DD>
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Both
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<B>O_CREAT</B>
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and
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<B>O_EXCL</B>
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were specified in
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<I>oflag</I>,
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but a semaphore with this
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<I>name</I>
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already exists.
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<DT id="3"><B>EINVAL</B>
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<DD>
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<I>value</I>
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was greater than
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<B>SEM_VALUE_MAX</B>.
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<DT id="4"><B>EINVAL</B>
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<DD>
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<I>name</I>
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consists of just "/", followed by no other characters.
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<DT id="5"><B>EMFILE</B>
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<DD>
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The per-process limit on the number of open file descriptors has been reached.
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<DT id="6"><B>ENAMETOOLONG</B>
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<DD>
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<I>name</I>
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was too long.
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<DT id="7"><B>ENFILE</B>
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<DD>
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The system-wide limit on the total number of open files has been reached.
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<DT id="8"><B>ENOENT</B>
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<DD>
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The
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<B>O_CREAT</B>
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flag was not specified in
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<I>oflag</I>
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and no semaphore with this
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<I>name</I>
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exists;
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or,
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<B>O_CREAT</B>
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was specified, but
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<I>name</I>
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wasn't well formed.
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<DT id="9"><B>ENOMEM</B>
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<DD>
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Insufficient memory.
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</DL>
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<A NAME="lbAG"> </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>sem_open</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="lbAH"> </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="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+sem_close">sem_close</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_getvalue">sem_getvalue</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_post">sem_post</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_unlink">sem_unlink</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_wait">sem_wait</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+sem_overview">sem_overview</A></B>(7)
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<A NAME="lbAJ"> </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="10"><A HREF="#lbAB">NAME</A><DD>
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<DT id="11"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="12"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="13"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="14"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="15"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="16"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="17"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="18"><A HREF="#lbAJ">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: 00:05:56 GMT, March 31, 2021
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