1.1.1 Connecting to the UNIX Computer

If you turn on your terminal and see a message from the UNIX computer that looks something like this:

login:

you can probably skip ahead to the section "Logging In" later in this chapter. Otherwise, browse through the next few sections and find the one that applies to you. (We can't cover every user's situation exactly. If none of these suggestions helps you enough, ask another UNIX user or your system administrator.)

1.1.2 Logging In

The process of making yourself known to the UNIX computer system and getting to your UNIX account is called logging in . Before you can start work, you must connect your terminal or window to the UNIX computer (see the previous sections). Then log in to UNIX and identify yourself. To log in, enter your username (usually your name or initials) and a private password. The password does not appear on the screen as you enter it.

When you log in successfully, you will get some system messages and finally the UNIX shell prompt (where you can enter UNIX commands). A successful login to the system named nutshell would look something like this:

O'Reilly & Associates, Inc.
nutshell.oreilly.com: Solaris UNIX version 2.5

login: john


Password:
Last login: Mon Nov  3 14:34:51 EST 1997 from joe_pc

------------- NOTICE TO ALL USERS -----------------
The hosts nutshell, mongo and cruncher will be down
for maintenance from 6 to 9 PM tonight.
---------------------------------------------------

My opinions may have changed, but not the fact that I am right.
Tue Nov  4 12:24:48 EST 1997
%

In this example, the system messages include a "fortune" and the date. Although this example doesn't show it, you may be asked for your terminal type , accounting or chargeback information, and so on. The last line to appear is the UNIX shell prompt. When you reach this point, you're logged in to your account and can start using UNIX commands.

Instead of a shell prompt, you may get a menu of choices ("email," "news," and so on). If one of the choices is something like "shell prompt" or "command prompt," select it. Then you'll be able to follow the descriptions and examples in this book.

The messages that appear when you log in differ from system to system and day to day. The shell prompt also differs. The examples in this book use the percentage sign as a prompt (% ).

Let's summarize logging in, step by step:

1. If needed, connect your terminal or window to the UNIX system.

2. If you don't have a "login:" prompt, press the [RETURN] key a few times until you see that prompt on the screen.

3. Type in your username in lowercase letters at the prompt. For example, if your login name is "john," type:

   login: john
   
   

   Press the [RETURN] key.

   The system should prompt you to enter your password. If passwords aren't used on your system, you can skip the next step.

4. If you were assigned a password, type it at the prompt. For security, your password is not displayed as you type it:

   Password:

   Press the [RETURN] key after you finish typing your password.

The system verifies your account name and password, and, if they're correct, logs you in to your account.

1.1.3 Remote Logins

The computer you log in to may not be the computer you need to use. For instance, you might have a workstation on your desk but need to do some work on the main computer in another building. Or you might be a professor doing research with a computer at another university.

Your UNIX system can probably connect to another computer to let you work as if you were sitting at the other computer. To do this, you first log in to your local computer. Then you start a program on your local computer that connects to the remote computer. Some typical programs are telnet and rlogin (for connecting over a computer network) as well as cu and tip (for connecting through telephone lines using a modem). You use the remote system until you're done; when you log off the remote computer, the remote-login program quits, and then returns you to your local computer.

The syntax for most remote-login programs is:

program-name remote-hostname

For example, if Dr. Nelson wanted to connect to the remote computer named biolab.medu.edu , she'd log in to her local computer (named fuzzy ) first. Next, she'd use the telnet program to reach the remote computer. Her session might look something like this:

login: jennifer


Password: 

NOTICE to all second-floor MDs: meeting in room 304 at 4 PM.

fuzzy% telnet biolab.medu.edu



Medical University Biology Laboratory

biolab.medu.edu login: jdnelson


Password:

biolab%
	.
	.
	.
biolab% exit


Connection closed by foreign host.
fuzzy%

Her accounts have shell prompts that include the hostname. This reminds her when she's logged in remotely. If you use more than one system but don't have the hostname in your prompt, references in Appendix A, Reading List (UNIX Power Tools , for example), will show you how to add it.

1.1.4 The UNIX Shell

Once you've logged in, you're working with a program called a shell . The shell interprets the commands you enter, runs the program you've asked for, and generally coordinates what happens between you and the UNIX operating system. Common shells include Bourne (sh ), Korn (ksh ), and C (csh ) shells, as well as bash and tcsh .

For a beginner, the differences between most shells are slight. If you plan to do a lot of work with UNIX, though, ask your system administrator which shell your account uses; you should learn more about your shell and its set of special commands.

1.1.5 The Shell Prompt

When the system finishes running a command, the shell replies with a prompt to tell you that you can enter another command line.

Shell prompts usually contain $ or % . The prompt can be customized, though, so your own shell prompt may be different.

1.1.6 Entering a Command Line

Entering a command line at the shell prompt tells the computer what to do. Each command line includes the name of a UNIX program. When you press [RETURN] , the shell interprets your command line and executes the program.

The first word that you type at a shell prompt is always a UNIX command (program name). Like most things in UNIX, command names are case-sensitive; if the command name is lowercase (and most are), you must type it in lowercase. Some simple command lines have just one word: the command name.

1.1.7 Correcting a Mistake

What if you make a mistake in a command line? Suppose you typed dare instead of date and pressed the [RETURN] key before you realized your mistake. The shell will give you an error message:

% dare


dare: command not found
%

Don't be too concerned about getting error messages. Sometimes you'll get an error even if it appears that you typed the command correctly. This can be caused by typing control characters that are invisible on the screen. Once the prompt returns, reenter your command.

Most modern shells let you recall previous commands and edit command lines. If you'll be doing a lot of work at the shell prompt, it's worth learning these handy techniques. They take more time to learn than we can spend here, though. Ask other users for help or read a reference book for your shell (see Appendix A ). We'll concentrate on simple methods that work with all shells.

If you see a mistake before you press [RETURN] , you can use the [BACKSPACE] key to erase the mistake and put in the correction.

The erase character differs from system to system and from account to account, and can be customized. The most common erase characters are:

• [BACKSPACE]

• [DELETE] , [DEL] , or [RUBOUT] key

• [CTRL-H]

[CTRL-H] is called a control character . To type a control character (for example, [CTRL-H] , hold down the [CTRL] key while pressing the letter "h". (This is like the way you make an uppercase letter: hold the [SHIFT] key while pressing a letter key.) In the text, we will write control characters as [CTRL-H] , but in the examples, we will use the standard notation: ^H . This is not the same as pressing the ^ (caret) key, letting go, and then typing an H!

The key labeled [DEL] may be used as the interrupt character instead of the erase character. (It's labeled [DELETE] or [RUBOUT] on some terminals.) This key is used to interrupt or cancel a command, and can be used in many (but not all) cases when you want to quit what you're doing. Another character often programmed to do the same thing is [CTRL-C] .

Some other common control characters are:

[CTRL-U]

Erases the whole input line; you can start over.

[CTRL-S]

Pauses output from a program that is writing to the screen.

[CTRL-Q]

Restarts output after a pause by [CTRL-S] .

[CTRL-D]

Used to signal end-of-input for some programs (like cat and mail ; see Chapter 3, Your UNIX Account ) and return you to a shell prompt. If you type [CTRL-D] at a shell prompt, it may also log you out of the UNIX system.

Find the erase and interrupt characters for your account and write them down:

_______ Backspace and erase a character

_______ Interrupt a command

In Chapter 3 , we'll tell you how to change these characters if you like.

1.1.8 Logging Out

To end a UNIX session, you must log out. You should not end a session by just turning off your terminal! To log out, enter the command exit . (In many cases, the command logout will also work.) Depending on your shell, you may also be able to log out by typing [CTRL-D] .

What happens next depends on the place from which you've logged in:

• If your terminal is connected directly to the computer, the "login:" prompt should appear on the screen.

• If you're using a window system, the window will probably close. If you have additional windows open, you'll need to log out or close them, too. You may also need to terminate the window system itself. (See Chapter 2 .)

• If you were connected to a remote computer, the system prompt from your local computer should reappear on your screen. (That is, you're still logged in to your local computer.) Repeat the process if you want to log out from the local computer.

After you've logged out, you can turn off your terminal or leave it on for the next user.