Callbacks can be done a number of ways, but it is very trivial to add a script to fire on a specific runlevel. For instance, in Ubuntu, you have the following [http://en.wikipedia.org/wiki/Runlevel#Ubuntu](http:// “Link title”)

A simple solution, would be to install / configure “postfix” and have a bash script run the ‘mail’ command found in the mail-utils package. If you’re going to power off the machine, you can place the script in /etc/rc0.d/ This of course, is run-level 0 or “halt”. If you do an 'ls -lt’ in that directory, you’ll notice that there are symlinks:

ls -lt
total 4.0K
lrwxrwxrwx 1 root root  17 Aug 26 13:28 K09apache2 -> ../init.d/apache2*
lrwxrwxrwx 1 root root  18 Aug  5 16:54 K79quotarpc -> ../init.d/quotarpc*
lrwxrwxrwx 1 root root  15 Aug  5 16:54 K85quota -> ../init.d/quota*
lrwxrwxrwx 1 root root  17 Jul  9 13:42 K08tomcat7 -> ../init.d/tomcat7*
lrwxrwxrwx 1 root root  20 May 20 12:39 K20virtualbox -> ../init.d/virtualbox*
lrwxrwxrwx 1 root root  29 May 20 12:31 K10unattended-upgrades -> ../init.d/unattended-upgrades*
lrwxrwxrwx 1 root root  20 May 20 12:23 S35networking -> ../init.d/networking*
lrwxrwxrwx 1 root root  18 May 20 12:23 S20sendsigs -> ../init.d/sendsigs*
lrwxrwxrwx 1 root root  22 May 20 12:23 S31umountnfs.sh -> ../init.d/umountnfs.sh*
lrwxrwxrwx 1 root root  18 May 20 12:23 S40umountfs -> ../init.d/umountfs*
lrwxrwxrwx 1 root root  20 May 20 12:23 S60umountroot -> ../init.d/umountroot*
lrwxrwxrwx 1 root root  14 May 20 12:23 S90halt -> ../init.d/halt*
lrwxrwxrwx 1 root root  17 May 20 12:23 S30urandom -> ../init.d/urandom*
-rw-r--r-- 1 root root 353 Jul 26  2012 README

What I would do, is find a logical place to store your callback script and symlink it here.

-Johnny Starr
[www.thestarrlab.com](http:// “The StarrLab”)