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update-motd(5) File Formats Manual 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 re-
mote 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 in-
formation.
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 /run/motd.dynamic. The order of
script execution is determined by the run-parts(8) --lsbsysinit option (basically alpha-
betical order, with a few caveats).
On Ubuntu systems, /etc/motd is typically a symbolic link to /run/motd.dynamic.
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=/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 in-
stance:
/etc/update-motd/05-lsb-release
#!/bin/sh
echo
lsb-release -a
FILES
/etc/motd, /run/motd.dynamic, /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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