If you ever need to enable the root user in Ubuntu 14.04 LTS linux installation, you can do so as follows:
Open a terminal window and type the following commands:
sudo su -c
Enter a strong password and restart the computer.
To make sure that you can login as root, open a new terminal window and at the $ prompt, enter:
Enter the root password. If you get the # prompt, then you are logged in as the root user.
Now you can manage the system by explicitly logging in as root user.
There could be a need to disable root login. You can do that in a terminal window as follows:
sudo passwd -dl root