ubuntu add printer

Now if you want to add a printer, you must come here.
http://localhost:631
Because, the GUI for printer installation in Ubuntu using current user while not root, so no way to pass the authorization check. The web UI can put in root user and password, so it's better.

Another issue is that the default setting of Ubuntu have no root password, so
sudo passwd
to create a password for the Unix system. Then when you add printer from the web UI, it will work.