Execute a command at shutdown

To dismount TrueCrypt volumes at shutdown and reboot time, I created a script, put it in/etc/init.d/ and symlinked it into the needed /etc/rc?.d/ directories using update-rc.d.
Here is the detail:

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/etc/init.d/truecrypt:
#!/bin/bash

case "$1" in
  start)
	#do nothing; I will mount the volume I need when I need it
	;;
  stop)
	#dismount all volumes
	truecrypt -d
	;;
  *)
	echo $"Usage: $0 -d"
	exit 1
esac

exit $?

Then I launched this command:

update-rc.d truecrypt stop 25 0 1 6 .

that created these symbolic links:

/etc/rc0.d/K25truecrypt -> ../init.d/truecrypt
/etc/rc1.d/K25truecrypt -> ../init.d/truecrypt
/etc/rc6.d/K25truecrypt -> ../init.d/truecrypt

It means that at runlevel 0, 1 and 6 (halt, single-user and reboot) /etc/init.d/truecrypt stop will be executed after all the scripts with the name starting in K, for kill, and coming before it in alphabetical order.
If I wanted to run a script at start too I would symlink the script like this:

update-rc.d myscript start 25 2 3 4 5 . stop 25 0 1 6 .

It means that at runlevel 2, 3, 4 and 5 (multiuser runlevels) /etc/init.d/myscript start would be executed after all the scripts with the name starting in S, for start, in alphabetical order, and at runlevel 0, 1 and 6 /etc/init.d/myscript stop will be executed.
man init or debian.org for more info about runlevel.

Posted by: Z24 | Sun, Aug 27 2006 | Category: /linux | Permanent link | home
Tagged as: command-line, linux, programming, script, shell

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