1. Open the terminal and type:
    sudo passwd root
  2. When you see the prompt that says "Enter new UNIX password", enter the password you want for the root user and confirm it.
  3. Type
    sudo gedit /etc/X11/gdm/gdm.conf
  4. Locate the line that says
    Change it to
  5. Save the file
  6. Exit gedit, logout and then reboot.