Section 3: Logging In and Logging Out

To ensure security and organization on a system with many users, UNIX machines employ a system of user accounts. The user accounting features of UNIX provide a basis for analysis and control of system resources, preventing any user from taking up more than his or her share, and preventing unauthorized people from accessing the system. Every user of a UNIX system must get permission by some access control mechanism.

Logging in

Logging in to a UNIX system requires two pieces of information: A username, and a password. When you sit down for a UNIX session, you are given a login prompt that looks like this:

login:

Type your username at the login prompt, and press the return key. The system will then ask you for your password. When you type your password, the screen will not display what you type.

Your username

Your username is assigned by the person who creates your account. Your username must be unique on the system where your account exists since it is the means by which you are identified on the system.

Your password

When your account is created, you are promted to choose a password. Some guidlines to follow when selecting a password are:

• Do not use any part of your name, your spouse's name, your child's name, your pet's name, or anybody's name. Do not use any backward spellings of any name, either.
• Do not use any number that can be easily guessed, like your phone number, your social security number, your address, license plate number, etc.
• Do not use any word that can be found in an English or foreign-language dictionary.
• Do not use all the same letter, or a simple sequence of keys on the keyboard, like "qwerty".
• Do use a mix of upper-case and lower-case letters, numbers, and control characters.
• Do use at least six characters.

If you have accounts on multiple machines, use a different password on each machine. Do not choose a password that is so difficult to remember that you must write it down.

Logging Out

When you're ready to quit, type the command

exit

Before you leave your terminal, make sure that you see the login prompt, indicating that you have successfully logged out. If you have left any unresolved processes, the UNIX system will require you to resolve them before it will let you log out.