sudo passwd ubuntu
Then create your password, you will need to already be in Terminal
Ubuntu user: You will have to sudo once you login to do anything powerful
To create a usable root user’s account on a live cd, you can set the root password then su. This has not been possible in previous versions of Ubuntu as their user model made you remember to sudo before each command requiring root access.
sudo passwd root
It’s easier just to sudo command for one time use, instead of creating a root user to su to.
As of Ubuntu 9.10, I haven’t been able to login with “demo” or “Ubuntu” as the password for live session username “Ubuntu”.
If you are running most other types of linux like Debian, Red Hat, Mepis, Suse and others, they have an actual root user with an account.
If you’ve forgot your root password and need to reset it, Make Magazine has a nice writeup here: