Enabling hibernation in Ubuntu server 12.04

In Ubuntu 12.04 and newer, hibernation has been disabled by default in policykit.

Type the following command:

sudo nano /etc/polkit-1/localauthority/50-local.d/com.ubuntu.enable-hibernate.pkla

Fill it with this:

[Re-enable hibernate by default]
Identity=unix-user:*
Action=org.freedesktop.upower.hibernate
ResultActive=yes

Save by pressing Ctrl-O then enter and then exit nano by pressing Ctrl-X.