There are a couple of ways to activate root user account in Ubuntu. One of which is good for CLI (Command Line Interface) and the other for GUI (Graphical User Interface).
To activate root account in CLI, type the following:
sudo -s
A password prompt will appear to which admin password would suit.
Turning on root account in GUI use:
sudo passwd root
sudo sh -c 'echo "greeter-show-manual-login=true" >> /etc/lightdm/lightdm.conf'
After reboot choose to login as root.
By privilege15