Creating A New *Nix User

The easiest way to create a new user on the command line is:
sudo useradd george
sudo passwd george

But that's not always enough. Let's say, for instance that you want people to change their password the first time that they log in and then again every three weeks. Let's set georgette up like that:
sudo useradd georgette -c "Georgette Userina"
sudo passwd georgette
(give her a throw-away password)
sudo passwd -e -x 21 georgette


Here's what we just did:
sudo = "superuser do" (do this as if you are root)
add user georgette with the comment (-c) "Georgette Userina" (-c is usually used for the user's full name)
give georgette a password she can use the first time she logs in
expire georgette's password immediately (so she has to change it when she next logs in) and then expire (-x) her password every 21 days.

Need a short term user? Maybe you have a contractor working with your company for a short time or a friend that's hanging out at your house for the next two weeks and needs access to your Ubuntu desktop while he's there. Here's how to do it:
sudo useradd sammi -c "Sammi Shortimer" -e 2008-03-10


Here we use the -e option with useradd to expire the account after March 10, 2008.

If you do most of your new user adds with the same special options, you can set those things as default in the file /etc/login.defs