Enabling the root account
Enabling the Root account is rarely necessary. Almost everything you need to do as administrator of an Ubuntu system can be done via sudo or gksudo. If you really need a persistent Root login, the best alternative is to simulate a Root login shell using the following command...
To enable the Root account (i.e. set a password) use:
sudo passwd root
Use at your own risk!
Logging in to X as root may cause very serious trouble. If you believe you need a root account to perform a certain action, please consult the official support channels first, to make sure there is not a better alternative.
Re-disabling your root account
If for some reason you have enabled your root account and wish to disable it again, use the following command in terminal...
sudo passwd -dl root