[ubuntu] root password lost while upgrading to Ubuntu 12.04

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http://ubuntuforums.org – While studying "Learning the Shell" As I try terminal entries, I GET 'Permission Denied". Then I try "su" to become the root user. When I use the password that I entered as I installed Ubuntu 11.04, I get Authentication failure. and cannot use the lesson commands. I am the sole user and should be able to be root user. when I am a user (not root) the password I use after the session timed out works properly. When I updated to Ubuntu 12.04, I had no opportunity to enter a password. How do I get to What the computer has for root password? (Hardware)