By default root user account is disabled for login in Ubuntu. Steps mentioned below will allow you to enable the root user and login as root on the OS.
- Login to your account and open Terminal
- sudo passwd root
- Type in the new password for UNIX
- sudo gedit /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
- At the end of the file append greeter
-show-manual–login = true
That’s all, now reboot the system and you can login to root account using manual login.