March 4, 2011, 5:50 p.m.
posted by juff
Every UNIX user has a username and password. Your system administrator assigns you a username and a password. Although you can and should change your password from time to time, you’re stuck with your username.
Before you can start work, you must prove your bona fides by logging in; that is, by typing your username and password. How hard can typing two words be? Really, now. The problem is this: Because of a peculiarity of human brain wiring, you will find that you can’t enter your username and password without making a typing mistake. It doesn’t matter whether your username is al — you will type Al, la, a;L, and every other possible combination.
Tip UNIX always considers upper- and lowercase letters to be different: If your username (sometimes also called your login name) is egbert, you must type it exactly that way. Don’t type Egbert, EGBERT, or anything else. Yes, we know that your name is Egbert and not egbert, but your computer doesn’t know that. UNIX usernames almost always are written entirely in lowercase. Pretend that you’re a disciple of e. e. cummings.
When you type your username and password and make a mistake, you may be tempted to press Backspace to clear your mistake. If only life were that easy. Guess how you clear typing errors when you type your username and password? You press the # key, of course! (We’re sure that it made sense in 1975.) Some — but not all — versions of UNIX have changed so that you can use Backspace or Delete; you may have to experiment. If you want UNIX to ignore everything you typed, press @, unless your version of UNIX has changed the command key to Ctrl+U (for untype, presumably — doubleplusungood). So, Egbert (as you typed your username), you may have typed something like this:
ttyS034 login: Eg##egberq#t
Finish entering your username by pressing Enter or Return.
After you type your username, UNIX asks you to enter your password, which you type the same way and end by pressing Enter (or Return, but we call it Enter). Because your password is secret, it doesn’t appear on-screen as you type it. How can you tell whether you typed it correctly? You can’t! If UNIX agrees that you typed your username and password acceptably, it displays a variety of uninteresting legal notices and a message from your system administrator (usually delete some files, the disk is full) and passes you on to the shell, which you find out about in Chapter 2.
If UNIX did not like either your username or your password, UNIX says Login incorrect and tells you to start over with your username.
Warning In the interest of security, UNIX asks you for a password even if you type your username wrong. This arrangement confuses the bad guys — but not nearly as much as it confuses regular users. So, if UNIX rejects your password even though you’re sure that you typed it correctly, maybe you typed your username incorrectly.