3.6. Tip for Changing Account Setup: Keep a Shell Ready

The shell is your interface to Unix. If you make a bad mistake when you change your setup file (Section 3.3) or your password, it can be tough to log in and fix things.

Before you change your setup, it's a good idea to start a login session to the same account from somewhere else. Use that session for making your changes. Log in again elsewhere to test your changes.