I have a LiveCD started as a default user. How to login as root?Here it is said that there are boot parameters. How and when to set them? 
How to login as superuser\administrator in Scientific Linux 6 LiveCD?
root;not root user;livecd;scientific linux
Have you tried just using su?Most of the time the default user on a livecd has passwordless sudo, and can also su passwordlessly to any other user.