Grant users shutdown and reboot privilege

This far in my Xmonad setup I've had to su as root to shutdown or reboot.  Use sudo to allow normal users to shutdown the system. Install the sudo package.

ROOTPROMPT$> apt-get install sudo

UPDATE: The /etc/sudoers file (at least since sudo 1.8.5) suggests adding local content to /etc/sudoers.d instead of altering the /etc/sudoers file with visudo.  I created the following power_conf file to have the same effect as the visudo method described later:

#/etc/sudoers.d/poweroff_conf
[USERNAME] [HOST] = NOPASSWD: /sbin/shutdown -h now, /sbin/poweroff, /sbin/reboot

The manual suggest 0440 permissions for all files in this directory.

ROOTPROMPT$> chmod 0440 /etc/sudoers.d/power_conf

Previous Method: The old way to grant normal users these privileges is to directly modify the /etc/sudoers file using visudo (installed with the sudo package).

#/etc/sudoers
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the man page for details on how to write a sudoers file.
#

Defaults        env_reset

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification
root    ALL=(ALL) ALL

# Allow members of group sudo to execute any command
# (Note that later entries override this, so you might need to move
# it further down)
%sudo ALL=(ALL) ALL
[USERNAME] [HOSTNAME] = NOPASSWD: /sbin/shutdown -h now, /sbin/poweroff, /sbin/reboot
#
#includedir /etc/sudoers.d

Add the highlighted line to your /etc/sudoers file, substituting your username for [USERNAME] and your hostname for [HOSTNAME].  The 'NOPASSWD' command lets the user issue these commands without entering their password.  This command gives shutdown, poweroff, and reboot privileges to the user, but only for the commands issued exactly as entered in this file.  For example, to shutdown as user:

USERPROMPT$ sudo /sbin/shutdown -h now 

will work, but

USERPROMPT$ sudo /sbin/shutdown

will not.  I learned how to set this up from http://www.debian-administration.org/articles/33.  Be careful which privileges you grant to users.