257 lines
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257 lines
6.6 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 CRONTAB</TITLE>
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</HEAD><BODY>
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<H1>CRONTAB</H1>
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Section: User Commands (1)<BR>Updated: 19 April 2010<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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crontab - maintain crontab files for individual users (Vixie Cron)
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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crontab [ -u user ] file
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<BR>
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crontab [ -u user ] [ -i ] { -e | -l | -r }
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<I>crontab</I>
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is the program used to install, deinstall or list the tables
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used to drive the
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<I><A HREF="/cgi-bin/man/man2html?8+cron">cron</A></I>(8)
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daemon in Vixie Cron. Each user can have their own crontab, and though
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these are files in /var/spool/cron/crontabs,
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they are not intended to be edited directly.
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<P>
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If the
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<I>/etc/cron.allow</I>
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file exists, then you must be listed (one user per line) therein in order to be
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allowed to use this command. If the
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<I>/etc/cron.allow</I>
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file does not exist but the
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<I>/etc/cron.deny</I>
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file does exist, then you must <B>not</B> be listed in the
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<I>/etc/cron.deny</I>
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file in order to use this command.
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<P>
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If neither of these files exists, then depending on site-dependent
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configuration parameters, only the super user will be allowed to use this
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command, or all users will be able to use this command.
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<P>
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If both files exist then
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<I>/etc/cron.allow</I>
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takes precedence. Which means that
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<I>/etc/cron.deny</I>
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is not considered and your user must be listed in
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<I>/etc/cron.allow</I>
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in order to be able to use the crontab.
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<P>
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Regardless of the existence of any of these files, the root administrative
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user is always allowed to setup a crontab. For standard Debian systems, all
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users may use this command.
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<P>
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If the
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<I>-u</I>
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option is given, it specifies the name of the user whose crontab is to be
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used (when listing) or modified (when editing). If this option is not given,
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<I>crontab</I>
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examines "your" crontab, i.e., the crontab of the person executing the
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command. Note that
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<I><A HREF="/cgi-bin/man/man2html?8+su">su</A></I>(8)
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can confuse
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<I>crontab</I>
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and that if you are running inside of
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<I><A HREF="/cgi-bin/man/man2html?8+su">su</A></I>(8)
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you should always use the
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<I>-u</I>
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option for safety's sake.
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<P>
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The first form of this command is used to install a new crontab from some
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named file or standard input if the pseudo-filename ``-'' is given.
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<P>
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The
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<I>-l</I>
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option causes the current crontab to be displayed on standard output. See
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the note under
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<B>DEBIAN SPECIFIC</B>
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below.
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<P>
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The
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<I>-r</I>
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option causes the current crontab to be removed.
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<P>
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The
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<I>-e</I>
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option is used to edit the current crontab using the editor specified by
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the <FONT SIZE="-1">VISUAL</FONT> or <FONT SIZE="-1">EDITOR</FONT> environment variables.
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After you exit
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from the editor, the modified crontab will be installed automatically. If
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neither of the environment variables is defined, then the
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default editor /usr/bin/editor is used.
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<P>
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The
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<I>-i</I>
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option modifies the -r option to prompt the user for a 'y/Y' response
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before actually removing the crontab.
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<A NAME="lbAE"> </A>
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<H2>DEBIAN SPECIFIC</H2>
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The "out-of-the-box" behaviour for
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<I>crontab -l</I>
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is to display the three line "DO NOT EDIT THIS FILE" header
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that is placed at the
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beginning of the crontab when it is installed. The problem is that
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it makes the sequence
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<P>
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crontab -l | crontab -
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<P>
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non-idempotent --- you keep adding copies of the header. This causes
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pain to scripts that use sed to edit a crontab. Therefore, the default
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behaviour of the
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<B>-l</B>
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option has been changed to not output such header. You may obtain the
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original behaviour by setting the environment variable
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<B>CRONTAB_NOHEADER</B>
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to 'N', which will cause the
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<I>crontab -l</I>
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command to emit the extraneous header.
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<A NAME="lbAF"> </A>
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<H2>SEE ALSO</H2>
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<A HREF="/cgi-bin/man/man2html?5+crontab">crontab</A>(5), <A HREF="/cgi-bin/man/man2html?8+cron">cron</A>(8)
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<A NAME="lbAG"> </A>
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<H2>FILES</H2>
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<PRE>
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/etc/cron.allow
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/etc/cron.deny
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/var/spool/cron/crontabs
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</PRE>
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<P>
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The files
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<I>/etc/cron.allow</I>
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and
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<I>/etc/cron.deny</I>
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if, they exist, must be either world-readable, or readable by group
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``crontab''. If they are not, then cron will deny access to all users until the
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permissions are fixed.
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<P>
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There is one file for each user's crontab under the /var/spool/cron/crontabs
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directory. Users are not allowed to edit the files under that directory
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directly to ensure that only users allowed by the system to run periodic tasks
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can add them, and only syntactically correct crontabs will be written there.
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This is enforced by having the directory writable only by the
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<I>crontab</I>
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group and configuring
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<I>crontab</I>
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command with the setgid bid set for that specific group.
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<A NAME="lbAH"> </A>
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<H2>STANDARDS</H2>
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The
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<I>crontab</I>
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command conforms to IEEE Std1003.2-1992 (``POSIX''). This new command syntax
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differs from previous versions of Vixie Cron, as well as from the classic
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SVR3 syntax.
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<P>
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<A NAME="lbAI"> </A>
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<H2>DIAGNOSTICS</H2>
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A fairly informative usage message appears if you run it with a bad command
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line.
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<P>
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cron requires that each entry in a crontab end in a newline character. If the
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last entry in a crontab is missing the newline, cron will consider the crontab
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(at least partially) broken and refuse to install it.
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<P>
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The files under
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<I>/var/spool/cron/crontabs</I>
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are named based on the user's account name.
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Crontab jobs will not be run for users whose accounts have been
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renamed either due to changes in the local system or because they are
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managed through a central user database (external to the system, for
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example an LDAP directory).
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<P>
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<P>
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<A NAME="lbAJ"> </A>
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<H2>AUTHOR</H2>
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Paul Vixie <<A HREF="mailto:paul@vix.com">paul@vix.com</A>> is the author of
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<I>cron</I>
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and original creator of this manual page. This page has also been modified for
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Debian by Steve Greenland, Javier Fernandez-Sanguino and Christian Kastner.
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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="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">DEBIAN SPECIFIC</A><DD>
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<DT id="5"><A HREF="#lbAF">SEE ALSO</A><DD>
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<DT id="6"><A HREF="#lbAG">FILES</A><DD>
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<DT id="7"><A HREF="#lbAH">STANDARDS</A><DD>
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<DT id="8"><A HREF="#lbAI">DIAGNOSTICS</A><DD>
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<DT id="9"><A HREF="#lbAJ">AUTHOR</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: 00:05:09 GMT, March 31, 2021
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