The hibernate menu is disabled by default in ubuntu 12.04 due to some reasons like it din’t work in many computers. So you can re-enable it in ubuntu 12.04. Here is how you can enable hibernate in ubuntu 12.04 LTS.
Be Safe – Always save your work before hibernating.
First check if hibernate works correctly in your system. You can use the command line to test if hibernate works on your computer.
a. Open the Terminal by pressing Ctrl+Alt+t or by searching for terminal in the dash.
b. Now type
sudo pm-hibernate into the terminal and press Enter.
Enter your password when asked.
c. After the computer turns off, switch it back on. Did your open applications re-open?
If hibernate doesn’t work, check if your swap partition is at least as large as your available RAM.
To enable the hibernate option in the menus, use your favorite text editor to create/edit
/etc/polkit-1/localauthority/50-local.d/com.ubuntu.enable-hibernate.pkla file. Add the following to the file and save:
[Re-enable hibernate by default]
Restart your computer and hibernate option is back!
killall unity-panel-service to just reset the menu.
Some users will then need to run
sudo update-grub to get the hibernate option to be available in the power menu.
You can follow official documentation here.