Many of you might have noticed that Hibernation is disabled in Ubuntu 12.04 by default because in Ubuntu, hibernate often don’t work on new hardware models without software fixes and it would be unprofessional to provide hibernation option which will not work on some machines. That is why you do not see hibernation ability on latest Ubuntu 12.04 beta release.
Contrary disabling entirely a working hibernation functionality which will not work on some machines is not a good practice too. Fortunately there is a workaround to tackle with this situation. Thanks to dima from Ask Ubuntu.
To enable hibernation in Ubuntu 12.04 you need to edit policykit files, just follow these commands
sudo gedit /etc/polkit-1/localauthority/50-local.d/com.ubuntu.desktop.pkla
[Re-enable hibernate by default] Identity=unix-user:* Action=org.freedesktop.upower.hibernate ResultActive=yes
Now you need to restart your system, after restart you will see hibernation option.