How do I set the root password so I can use su instead of sudo on Ubuntu

Warning: Directly logging in as root is like playing with fire, because one little typo is enough to lose critical data or make your system unbootable. Note that desktop environments will also function incorrectly if you login to them as root.

See these questions for the reasons behind why sudo is preferred and why root-login is disabled by default:

• What are the benefits of sudo over su?
• Why is there no option to login as root?

# sudo -i
# passwd