My Ubuntu 12.04 is missing Hibernate option so after searching a little on Google I came to know that this can solve my problem
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
Here is the link : How to enable hibernation in 12.04?
After doing this I restarted my system. when the system booted it hanged ike anything No mouse movement no terminal no nothing. I waited for more than 1 hour Hibernate option appeared but i was not able to use my system anymore. any ideas ?