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This section covers what to do if you have a problem logging in, how to use virtual consoles, how to log in remotely, and how to change your password.
What to Do If You Cannot Log In
When you enter your username or password incorrectly, the system displays an error message after you enter both your username and your password. This message indicates that you have entered either the login name or the password incorrectly or that they are not valid. It does not differentiate between an unacceptable login name and an unacceptable password to discourage unauthorized people from guessing names and passwords to gain access to the system. Some common reasons that logins fail are listed here:
Refer to "Changing Your Password" on page 37 when you want to change your password.
To log out from a character-based interface, press CONTROL-D or give the command exit in response to the shell prompt.
Using Virtual Consoles
When running Linux on a personal computer, you frequently work with the display and keyboard attached to the computer. Using this physical console, you can access as many as 63 virtual consoles (also called virtual terminals). Some are set up to allow logins, whereas others act as graphical displays. To switch between virtual consoles, hold down the CONTROL and ALT keys and press the function key that corresponds to the console you want to view. For example, CONTROL-ALT-F5 displays the fifth virtual console. This book refers to the console that you see when you first boot a system (or press CONTROL-ALT-F1) as the system console (or just console).
Typically, six virtual consoles are active and have text login sessions running. When you want to use both a character-based interface and a GUI, you can set up a character-based session on one virtual console and a graphical session on another. Whichever virtual console you start a graphical session from, the graphical session finds the first unused virtual console (typically number seven).
Changing Your Password
If someone else assigned you a password, it is a good idea to give yourself a new one. A good password is seven or eight characters long and contains a combination of numbers, uppercase and lowercase letters, and punctuation characters. Avoid using control characters (such as CONTROL-H) because they may have a special meaning to the system, making it impossible for you to log in. Do not use names, words from English or other languages, or other familiar words that someone can easily guess.
For security reasons none of the passwords you enter is ever displayed by any utility.
security: Protect your password
Do not allow someone to find out your password: Do not put your password in a file that is not encrypted, allow someone to watch you type your password, give it to someone you do not know (a system administrator never needs to know your password), or write it down.
security: Choose a password that is difficult to guess
Do not use phone numbers, names of pets or kids, birthdays, words from a dictionary (not even a foreign language), and so forth. Do not use permutations of these items.
security: Differentiate between important and less important passwords
It is important to differentiate between important and less important passwords. For example, Web site passwords for blogs or download access are not very important; it is not bad if you choose the same password for these types of sites. However, your login, mail server, and bank account Web site passwords are critical: Never use these passwords for an unimportant Web site.
To change your password, give the command passwd from a command line:
$ passwd Changing password for user zach. Changing password for zach (current) UNIX password: New UNIX password: Retype new UNIX password: passwd: all authentication tokens updated successfully.
The first item the system asks you for is your current (old) password. This password is verified to ensure that an unauthorized user is not trying to alter your password. Next the system requests the new password.
A password should meet the following criteria to be relatively secure. Only the first item is mandatory.
After you enter your new password, the system asks you to retype it to make sure you did not make a mistake when you entered it the first time. If the new password is the same both times you enter it, your password is changed. If the passwords differ, it means that you made an error in one of them, and the system displays an error message:
Sorry, passwords do not match
If your password is not long enough, the system displays the following message:
BAD PASSWORD: it is too short
When it is too simple, the system displays this message:
BAD PASSWORD: it is too simplistic/systematic
When it is formed from words, the system displays this message:
BAD PASSWORD: it is based on a dictionary word
If you get one of these messages you need to start over. Press RETURN a few times until the shell displays a prompt and run passwd again.
When you successfully change your password, you change the way you log in. If you forget your password, Superuser can change it and tell you your new password.
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