How to Enable and Disable Ubuntu Root Password
Ubuntu is one of the few Linux distributions out there that will not enable the root account.If you want to do something with root permission on the console you have to type sudo before the command.
sudo" means superuser do. "sudo" will prompt for "Password:". Please specify user password
As you have noticed during the Ubuntu installation there was no question about the root password, as you might have been used to see during other Linux distribution installation process.Because of this your root accout is inactive.
If you want to enable root account (which is not recommended) enter the following command.