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Linux 2.6 - man page for update-motd (linux section 5)

update-motd(5)									   update-motd(5)

NAME
       update-motd - dynamic MOTD generation

SYNOPSIS
       /etc/update-motd.d/*

DESCRIPTION
       UNIX/Linux  system  adminstrators  often  communicate important information to console and
       remote users by maintaining text  in  the  file	/etc/motd,  which  is  displayed  by  the
       pam_motd(8) module on interactive shell logins.

       Traditionally,  this file is static text, typically installed by the distribution and only
       updated on release upgrades, or overwritten by  the  local  administrator  with	pertinent
       information.

       Ubuntu introduced the update-motd framework, by which the motd(5) is dynamically assembled
       from a collection of scripts at login.

       Executable scripts in /etc/update-motd.d/* are executed by pam_motd(8) as the root user at
       each  login,  and  this information is concatenated in /var/run/motd.  The order of script
       execution is determined by the run-parts(8) --lsbsysinit  option  (basically  alphabetical
       order, with a few caveats).

       On Ubuntu systems, /etc/motd is typically a symbolic link to /var/run/motd.

BEST PRACTICES
       MOTD  fragments	must  be scripts in /etc/update-motd.d, must be executable, and must emit
       information on standard out.

       Scripts should be named named NN-xxxxxx where NN is a two digit	number	indicating  their
       position in the MOTD, and xxxxxx is an appropriate name for the script.

       Scripts must not have filename extensions, per run-parts(8) --lsbsysinit instructions.

       Packages  should  add  scripts  directly  into /etc/update-motd.d, rather than symlinks to
       other scripts, such that administrators can modify or remove these  scripts  and  upgrades
       will  not  wipe the local changes.  Consider using a simple shell script that simply calls
       exec on the external utility.

       Long running operations (such as network calls) or resource intensive scripts should cache
       output, and only update that output if it is deemed expired.  For instance:

	 /etc/update-motd.d/50-news
	 #!/bin/sh
	 out=/var/run/foo
	 script="w3m -dump http://news.google.com/"
	 if [ -f "$out" ]; then
	   # Output exists, print it
	   echo
	   cat "$out"
	   # See if it's expired, and background update
	   lastrun=$(stat -c %Y "$out") || lastrun=0
	   expiration=$(expr $lastrun + 86400)
	   if [ $(date +%s) -ge $expiration ]; then
	     $script > "$out" &
	   fi
	 else
	   # No cache at all, so update in the background
	   $script > "$out" &
	 fi

       Scripts	should	emit  a  blank line before output, and end with a newline character.  For
       instance:

	 /etc/update-motd/05-lsb-release
	 #!/bin/sh
	 echo
	 lsb-release -a


FILES
       /etc/motd, /var/run/motd, /etc/update-motd.d

SEE ALSO
       motd(5), pam_motd(8), run-parts(8)

AUTHOR
       This manpage and the update-motd framework was written by Dustin Kirkland <kirkland@canon-
       ical.com>  for Ubuntu systems (but may be used by others).  Permission is granted to copy,
       distribute and/or modify this document under the terms of the GNU General Public  License,
       Version 3 published by the Free Software Foundation.

       On  Debian  systems,  the  complete text of the GNU General Public License can be found in
       /usr/share/common-licenses/GPL.

update-motd				  13 April 2010 			   update-motd(5)


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