270 lines
6.1 KiB
HTML
270 lines
6.1 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 AIO_READ</TITLE>
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</HEAD><BODY>
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<H1>AIO_READ</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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aio_read - asynchronous read
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/aio.h">aio.h</A>></B>
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<P>
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<B>int aio_read(struct aiocb *</B><I>aiocbp</I><B>);</B>
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<P>
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Link with <I>-lrt</I>.
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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>aio_read</B>()
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function queues the I/O request described by the buffer pointed to by
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<I>aiocbp</I>.
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This function is the asynchronous analog of
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<B><A HREF="/cgi-bin/man/man2html?2+read">read</A></B>(2).
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The arguments of the call
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<P>
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<BR> read(fd, buf, count)
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<P>
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correspond (in order) to the fields
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<I>aio_fildes</I>,
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<I>aio_buf</I>,
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and
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<I>aio_nbytes</I>
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of the structure pointed to by
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<I>aiocbp</I>.
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(See
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<B><A HREF="/cgi-bin/man/man2html?7+aio">aio</A></B>(7)
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for a description of the
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<I>aiocb</I>
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structure.)
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<P>
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The data is read starting at the absolute position
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<I>aiocbp->aio_offset</I>,
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regardless of the file offset.
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After the call,
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the value of the file offset is unspecified.
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<P>
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The "asynchronous" means that this call returns as soon as the
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request has been enqueued; the read may or may not have completed
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when the call returns.
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One tests for completion using
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<B><A HREF="/cgi-bin/man/man2html?3+aio_error">aio_error</A></B>(3).
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The return status of a completed I/O operation can be obtained by
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<B><A HREF="/cgi-bin/man/man2html?3+aio_return">aio_return</A></B>(3).
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Asynchronous notification of I/O completion can be obtained by setting
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<I>aiocbp->aio_sigevent</I>
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appropriately; see
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<B><A HREF="/cgi-bin/man/man2html?7+sigevent">sigevent</A></B>(7)
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for details.
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<P>
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If
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<B>_POSIX_PRIORITIZED_IO</B>
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is defined, and this file supports it,
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then the asynchronous operation is submitted at a priority equal
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to that of the calling process minus
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<I>aiocbp->aio_reqprio</I>.
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<P>
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The field
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<I>aiocbp->aio_lio_opcode</I>
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is ignored.
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<P>
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No data is read from a regular file beyond its maximum offset.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, 0 is returned.
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On error, the request is not enqueued, -1
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is returned, and
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<I>errno</I>
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is set appropriately.
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If an error is detected only later, it will
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be reported via
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<B><A HREF="/cgi-bin/man/man2html?3+aio_return">aio_return</A></B>(3)
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(returns status -1) and
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<B><A HREF="/cgi-bin/man/man2html?3+aio_error">aio_error</A></B>(3)
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(error status---whatever one would have gotten in
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<I>errno</I>,
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such as
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<B>EBADF</B>).
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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>EAGAIN</B>
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<DD>
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Out of resources.
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<DT id="2"><B>EBADF</B>
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<DD>
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<I>aio_fildes</I>
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is not a valid file descriptor open for reading.
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<DT id="3"><B>EINVAL</B>
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<DD>
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One or more of
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<I>aio_offset</I>,
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<I>aio_reqprio</I>,
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or
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<I>aio_nbytes</I>
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are invalid.
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<DT id="4"><B>ENOSYS</B>
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<DD>
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<B>aio_read</B>()
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is not implemented.
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<DT id="5"><B>EOVERFLOW</B>
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<DD>
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The file is a regular file, we start reading before end-of-file
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and want at least one byte, but the starting position is past
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the maximum offset for this file.
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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>aio_read</B>()
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function is available since glibc 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>aio_read</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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It is a good idea to zero out the control block before use.
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The control block must not be changed while the read operation
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is in progress.
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The buffer area being read into
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must not be accessed during the operation or undefined results may occur.
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The memory areas involved must remain valid.
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<P>
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Simultaneous I/O operations specifying the same
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<I>aiocb</I>
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structure produce undefined results.
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<A NAME="lbAK"> </A>
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<H2>EXAMPLE</H2>
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See
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<B><A HREF="/cgi-bin/man/man2html?7+aio">aio</A></B>(7).
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+aio_cancel">aio_cancel</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+aio_error">aio_error</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+aio_fsync">aio_fsync</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+aio_return">aio_return</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+aio_suspend">aio_suspend</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+aio_write">aio_write</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+lio_listio">lio_listio</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+aio">aio</A></B>(7)
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<A NAME="lbAM"> </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">VERSIONS</A><DD>
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<DT id="12"><A HREF="#lbAH">ATTRIBUTES</A><DD>
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<DT id="13"><A HREF="#lbAI">CONFORMING TO</A><DD>
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<DT id="14"><A HREF="#lbAJ">NOTES</A><DD>
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<DT id="15"><A HREF="#lbAK">EXAMPLE</A><DD>
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<DT id="16"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="17"><A HREF="#lbAM">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: 00:05:35 GMT, March 31, 2021
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