Using Ubuntu server, how does one add an existing user to the sudo group (which is the “administrators” group in Ubuntu), thus granting that user pretty much full rights on the box?

Turns out that the answer is pretty much the same way you add a user to any other group in Ubuntu. If the user has already been created via the adduser command earlier (for argument’s sake, you named him bob), you simply now run the following command from the terminal:

sudo usermod -a -G sudo bob

Nifty.

(Note, if logged in, that user must first log off and then back in again for this change to take effect.)

super users