Normally, user cannot login as root in the login screen, because there are no password for root user in default. In order to login as root, a password for root user have to be set manually.
To set password for root user?
Start a Terminal and type the command:
sudo passwd
You will be as to type in the new root password twice. After that, re-login as root with the new password in login screen.
It's a personal blog/note/bookmark of a idiot in Linux.
