How do DE's call ACPI functions?

Okay, first off, this is not a problem I am facing, but I would like to understand this better. If I wish to shutdown / reboot my machine from the command line I need to call: $ sudo poweroff $ sudo reboot That is, I need root privileges to make these ACPI calls. However, I start my DE, (I use XFCE) without granting it root privileges: $ startxfce4 --with-ck-launch Now, I know that the --with-ck-launch parameter helps allows XFCE to shutdown / reboot my system, but I do not understand how. What allows ConsoleKit to shutdown without root privileges? How can it change the runlevel without super-user privileges? And since it is possible, how can I shutdown my machine from the console without root privileges?