Execute a command before shutdown

Question

I want to execute a simple command just before the computer shuts down (timing is not essential).

For startup I can use /etc/rc.local - is there something similar for shutdown?

Note that I would still like to use the integrated shutdown button from menu; i.e. I don't want to use a custom script everytime I shutdown via terminal - it needs to be automatical.

Answer 1

Linux Mint is based on Ubuntu, so I'm guesing the runlevel system is probably the same. On Ubuntu, scripts for the different runlevels are executed according to their presence in the /etc/rc[0-6].d directories. Runlevel 0 corresponds to shutdown, and 6 to reboot.

Typically the script itself is stored in /etc/init.d, and then symlinks are placed in the directories corresponding to the runlevels you require.

So in your case, write your script, store it in /etc/init.d/, then create a symlink in each of /etc/rc0.d and /etc/rc6.d (if you want both) pointing to your script.

The scripts in each runlevel directory will be executed in asciibetical order, so if the order within the runlevel matters to you, choose the name of your symlink accordingly.

Answer 2

You need to use rc.shutdown the shutdown script for the Linux Kernel. Quoting the OpenBSD man page:

When the system is shut down using the reboot(8) or halt(8) commands, or when init(8) is signalled to do so, or when a keyboard-requested halt is issued (if the architecture supports it), rc(8) is invoked with the argument ``shutdown''.

So, you simply open your rc.shutdown and add whatever shell commands you want to execute to it.

UPDATE: Since Linux Mint is based on Ubuntu, which has a different startup/shutdown procedure, here is the procedure relevant to you:

Write the shell script you wish to execute and copy it to the relevant directory in your /etc/rc*.d/. The * corresponds to the runlevel at which you want the script to execute.
Ubuntu follows the Debian runlevel numbering, so you have runlevel 0 for halt and runlevel 6 for reboot.