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5.9 KiB
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284 lines
5.9 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of POSIX_FALLOCATE</TITLE>
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</HEAD><BODY>
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<H1>POSIX_FALLOCATE</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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posix_fallocate - allocate file space
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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>
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<B>int posix_fallocate(int </B><I>fd</I><B>, off_t </B><I>offset</I><B>, off_t </B><I>len</I><B>);</B>
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</PRE>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>posix_fallocate</B>():
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<DL COMPACT><DT id="1"><DD>
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_POSIX_C_SOURCE >= 200112L
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The function
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<B>posix_fallocate</B>()
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ensures that disk space is allocated for the file referred to by the
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file descriptor
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<I>fd</I>
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for the bytes in the range starting at
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<I>offset</I>
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and continuing for
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<I>len</I>
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bytes.
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After a successful call to
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<B>posix_fallocate</B>(),
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subsequent writes to bytes in the specified range are
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guaranteed not to fail because of lack of disk space.
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<P>
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If the size of the file is less than
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<I>offset</I>+<I>len</I>,
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then the file is increased to this size;
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otherwise the file size is left unchanged.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<B>posix_fallocate</B>()
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returns zero on success, or an error number on failure.
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Note that
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<I>errno</I>
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is not set.
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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="2"><B>EBADF</B>
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<DD>
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<I>fd</I>
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is not a valid file descriptor, or is not opened for writing.
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<DT id="3"><B>EFBIG</B>
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<DD>
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<I>offset+len</I>
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exceeds the maximum file size.
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<DT id="4"><B>EINTR</B>
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<DD>
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A signal was caught during execution.
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<DT id="5"><B>EINVAL</B>
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<DD>
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<I>offset</I>
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was less than 0, or
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<I>len</I>
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was less than or equal to 0, or the underlying filesystem does not
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support the operation.
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<DT id="6"><B>ENODEV</B>
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<DD>
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<I>fd</I>
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does not refer to a regular file.
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<DT id="7"><B>ENOSPC</B>
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<DD>
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There is not enough space left on the device containing the file
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referred to by
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<I>fd</I>.
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<DT id="8"><B>ESPIPE</B>
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<DD>
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<I>fd</I>
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refers to a pipe.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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<B>posix_fallocate</B>()
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is available since glibc 2.1.94.
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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>posix_fallocate</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe (but see NOTES)<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.
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<P>
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POSIX.1-2008 says that an implementation
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<I>shall</I>
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give the
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<B>EINVAL</B>
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error if
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<I>len</I>
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was 0, or
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<I>offset</I>
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was less than 0.
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POSIX.1-2001 says that an implementation
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<I>shall</I>
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give the
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<B>EINVAL</B>
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error if
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<I>len</I>
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is less than 0, or
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<I>offset</I>
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was less than 0, and
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<I>may</I>
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give the error if
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<I>len</I>
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equals zero.
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<A NAME="lbAJ"> </A>
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<H2>NOTES</H2>
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In the glibc implementation,
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<B>posix_fallocate</B>()
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is implemented using the
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<B><A HREF="/cgi-bin/man/man2html?2+fallocate">fallocate</A></B>(2)
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system call, which is MT-safe.
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If the underlying filesystem does not support
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<B><A HREF="/cgi-bin/man/man2html?2+fallocate">fallocate</A></B>(2),
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then the operation is emulated with the following caveats:
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<DL COMPACT>
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<DT id="9">*<DD>
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The emulation is inefficient.
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<DT id="10">*<DD>
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There is a race condition where concurrent writes from another thread or
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process could be overwritten with null bytes.
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<DT id="11">*<DD>
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There is a race condition where concurrent file size increases by
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another thread or process could result in a file whose size is smaller
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than expected.
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<DT id="12">*<DD>
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If
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<I>fd</I>
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has been opened with the
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<B>O_APPEND</B>
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or
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<B>O_WRONLY</B>
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flags, the function fails with the error
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<B>EBADF</B>.
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</DL>
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<P>
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In general, the emulation is not MT-safe.
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On Linux, applications may use
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<B><A HREF="/cgi-bin/man/man2html?2+fallocate">fallocate</A></B>(2)
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if they cannot tolerate the emulation caveats.
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In general, this is
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only recommended if the application plans to terminate the operation if
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<B>EOPNOTSUPP</B>
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is returned, otherwise the application itself will need to implement a
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fallback with all the same problems as the emulation provided by glibc.
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+fallocate">fallocate</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+fallocate">fallocate</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+posix_fadvise">posix_fadvise</A></B>(2)
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<A NAME="lbAL"> </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="13"><A HREF="#lbAB">NAME</A><DD>
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<DT id="14"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="15"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="16"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="17"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="18"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="19"><A HREF="#lbAH">ATTRIBUTES</A><DD>
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<DT id="20"><A HREF="#lbAI">CONFORMING TO</A><DD>
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<DT id="21"><A HREF="#lbAJ">NOTES</A><DD>
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<DT id="22"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="23"><A HREF="#lbAL">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: 00:05:52 GMT, March 31, 2021
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