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. 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.
Your password
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
- passwd
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 didn't mistype. 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 password:
- 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 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 unresoved 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
- clear
right before you log out, or you can press the
return key until all the information is scrolled off the screen.