how to hibernate?

I am not able to hibernate my system.... i was able to hibernate when i had windows installed,but after installing ubuntu 10.04 i am not able to hibernate....

From ubuntu golu

• You should be able to click the menu at the top-right and select "Hibernate" from the options.

  "Log Out" is selected in this image. Just click the one below it.

  

  From mac9416

• If hibernate isn't working, that's a bug. Please file it: ubuntu-bug linux

  From maco