What are you trying to do ?
The "root" account on Ubuntu based systems is not activated and available .. DO NOT activate it unless you know what youre doing.
It's normally a good idea to steer clear of a root terminal and run commands that need root permissions with "sudo <command>"
If you MUST have a TRUE root prompt (denoted by a # prompt instead of a $ prompt), run:
enter YOUR password .. you will now be at a # prompt with elevated privileges, and your "Home" directory will be /root
To go back to a normal $ prompt run:
will get you a root prompt where your "Home" directory is still /home/<username>
will get you back to a normal $ prompt
BE CAREFUL whilst using "sudo su" .. anything written to YOUR "Home" directory will be written as root, with root as the owner .. which runs the risk of making your account unbootable.
MUCH safer to not use a root prompt at all, and just use "sudo" to run commands that need elevated privileges .. or "gksudo" if it's a GUI application.