# sudo passwd root
This command will immediately request to enter your password, and then re-enter the password again. Enter the correct password and the command line with the root account will be started.
To enable root accounts in Gnome, open the gdm.conf file, which is usually located at /etc/X11/gdm/gdm.conf and changes the AllowRoot condition to:
AllowRoot = true
Save this file. Exit Gnome and reopen it to activate your settings.