In ubuntu by default the
su (root) password is not not set. I have set it by using the
sudo passwd (see link). But I didn't like it. Can I go back to my original state.
The root account in Ubuntu is defaultly disabled. When you enabled the root account (set a password for it) then you can disble it easy by the following command:
sudo passwd -dl root
-dmeans to delete the password (make it empty)
-lmeans lock the password of the account