How To Shutdown Ubuntu Automatically X Minutes After Starting Up?

Question

How would one automatically shutdown an ubuntu OS 30 minutes after it was turned on? Or 15 minutes after it was turned on? Etc?

I tried creating an init.d script like so:

shutdown -h +5

But my box does not shut down after 5 minutes.

Answer 1

You could use cron and the @reboot flag to schedule the shutdown if you add this to the root crontab:
@reboot shutdown -h +30

Answer 2

/etc/init.d contains the launch scripts, but doesn't actually tell each runlevel what it should do. The actual scripts are called as symlinks from /etc/rc[0-6].d where [0-6] is the runlevel you're entering.

More specifically, the symlinks are given the name:

[SK]nnScript where [SK] is Start or Kill, nn is the order (lower first) and Script is the name of the file in /etc/init.d. Scripts scheduled to start are called with --start and those to be stopped --stop as switches.

On debian/ubuntu you can populate those scripts with:

update-rc.d --defaults <yourscript>

so that the appropriate symlinks get created in /etc/rc[0-6].d/

I'd strongly recommend though that you just symlink it yourself into runlevel 2 (default):

ln -s /etc/init.d/<myscript> /etc/rc2.d/S50<myscript>

As calling shutdown when shutting down (level 0), going single user (level 1) or rebooting (level 6) is probably not that wise an idea.