How to recover user password in ubuntu 12.04 ?

If you mean your login password there is no way to get it back, if you could it would not be very secure. You can reset it however: see here -

http://www.psychocats.net/ubuntu/resetpassword

or here

http://askubuntu.com/questions/24006/how-do-i-reset-a-lost-administrative-password

or here

http://www.howtogeek.com/howto/linux/reset-your-forgotten-ubuntu-password-in-2-minutes-or-less/

If you mean some other password. You will need to be more specific: What's the password for?

Thank you sir ,
I already have done with "http://www.psychocats.net/ubuntu/resetpassword" .
but I requested to enter root password, How can I get root password ?

It works for most people but there is another way. See here
https://help.ubuntu.com/community/LostPassword

There is no root password in Ubuntu. The account is disabled and there is no password, the root shell just drops to the prompt and you can reset any password there.

What is the output of:

lsb_release -a; uname -a

Thanks

actionparsnip , if he set a root password then the psychocat's website cannot save him.
Yes the root password is disabled by default , but you can enable it with 2-3 commands in terminal.

Then you cannot be dropped to a root shell if you don't give the root password.