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
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:
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 is assigned by the person who creates your account. At
ISU, the standard username is the first four letters of your last name
concatenated with the first four letters of your first name.
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.
When your account is created, a password is assigned. The first thing
you should do is change your password, using the passwd utility.
To change your password, type the command
after you have logged in. The system will ask for
your old password, to prevent someone else from sneaking up, and
changing your password. Then it will ask for your new password. You
will be asked to confirm your new password, to make sure that you
It is very important that you choose a good password, so that someone
else cannot guess it. Here are some rules for selecting a good
- 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 an easily-guessable number, 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
- 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.
When you're ready to quit, type the command
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. Some shells will
recognize other commands to log you out, like "logout" or even "bye".
It is always a good idea to clear the display before you log out, so
that the next user doesn't get a screenful of information about you,
your work, or your user account. You can type the command
right before you log out, or you can
press the return key until all the information is scrolled off the