Sudoers - Community Ubuntu Documentation

Shutting Down From The Console Without A Password

Often people want to be able to shut their computers down without requiring a password to do so. This is particularly useful in media PCs where you want to be able to use the shutdown command in the media centre to shutdown the whole computer.

To do this you need to add some cmnd aliases as follows:

Cmnd_Alias SHUTDOWN_CMDS = /sbin/shutdown, /sbin/halt, /sbin/reboot

You also need to add a user specification (at the end of the file after the "%admin ALL = (ALL) ALL" line so it takes effect - see above for details):

ALL=(ALL) NOPASSWD: SHUTDOWN_CMDS

Obviously you need to replace "" with the username of the user who needs to be able to shutdown the pc without a password. You can use a user alias here as normal.

via Sudoers - Community Ubuntu Documentation.