Introduction to Multics

SECTION 2

ENTERING AND LEAVING MULTICS

Entering the Multics system is called logging in, and leaving the system is called logging out.

USER IDENTIFICATION ON MULTICS

To successfully log in on Multics, you must be registered as a Multics user at your site. When you get registered, you are assigned your own identifying name, called a User id. Here is a sample User_id:

There are two components, separated "by a period, in this User_id: the Person id (PSissle), which is a unique (to Multics) version of Pam Sissle's name, and the Project id (Doc), an abbreviation of the name of the group she works with, which is included for administrative and accounting purposes. (A third component, the tag, is discussed in Section 7.)

Your User_id identifies you as a registered user, with authorization to use the resources of the system: computer time for interacting with the system and space (memory) to store the work you've done. Although your User_id is unique, it is public and can be known by everyone.

You also receive a preliminary password when you register. One of the first things you learn to do on the system is to change the assigned password to one you make up, so that it will be completely private. Your password ensures that only you can log in with your User_id because you are the only person who knows what your password is. The password system is the most important key to the security that Multics offers.

CONNECTING THE TERMINAL

Now you are a registered user, sitting at a terminal. After turning the terminal on (there is an on/off switch on the body of the terminal), you must make an electronic connection between it and the computer. Before you make this connection, the terminal is just another electric typewriter, with a few extra characters on the keyboard. (If you have a hardwired terminal - one that is connected directly and permanently to the computer - you are ready to turn to the next part of this section and log in.) This procedure is simple, but it differs slightly at each site. Your site probably has detailed instructions available. Here is a general description of terminal connection.

Terminal connection is made through normal telephone lines using a modem. The modem sends electronic signals to and from the terminal in the form of high-pitched tones. It may be built into the terminal, or it may be a separate unit connected by a cable to the terminal. If it is built in, you see only a cradle that accepts a telephone receiver, and there is a regular telephone nearby. Otherwise, you use a dataset, which looks very much like a regular telephone with several pushbuttons along it.

Pick up the telephone receiver, listen for a dial tone, and dial the phone number of your system (this number should be included with the instructions for your particular site, and may also be posted near the terminal). You will hear the phone ringing, and then a steady shrill tone when the connection is made. At this point, if you have a built-in modem, place the receiver firmly into the cradle, with the cord positioned as indicated on the unit. If your modem is a dataset, push the indicated button (labeled "DATA" or "HOLD") and then set the receiver back into its place on the modem. Usually, either the modem or the terminal turns on a small light when the connection is made. When this light goes off, it means you are disconnected.

Terminal connection sounds complicated, but it will become automatic for you very soon. If you have problems, make sure everything is plugged in and turned on, and ask another user for assistance.

Logging In

When you have successfully connected your terminal, Multics prints a banner, or greeting message. This is the signal for you to log in and identify yourself. Here is a sample login sequence for Pam Sissle, opening with a typical site banner. The lines are numbered for this example ONLY; the example is followed by an explanation of each line.

NOTE: Remember that you do NOT type exclamation points or line numbers to begin your command lines. Exclamation points are provided in this manual only as an aid to readers, to indicate lines that are typed by a user. Line numbers are used only for purposes of explanation.

1. The typical Multics banner is a two-line message giving the current version of Multics software, the name and location of your site, the number of people logged in, the total number of users the system can accept at one time, and the date and time.

2. The word "login" is the command (a command is a specific instruction to the computer) that identifies you and gives you access to Multics. Actions that you want performed by Multics are conveyed by commands.

Follow the login command with a space and your own Person_id and Project_id. Then press the RETURN key (this key may be labeled "RET" or "CR" on your terminal). All lines sent to Multics must be terminated by typing the RETURN key or else Multics will not act on them. This is a complete command line.

3. The login command is an interactive command: it responds to your Person_id and Project_id by requesting your password.

4. Both you and Multics use this line. First Multics prepares to conceal your password, so that nobody can read it. Depending on the kind of terminal you have, the printing of your password is either suppressed entirely or hidden in a string of cover-up characters. Then you type your password, and the RETURN key.

In this example, Pam Sissle typed in her preliminary password of "pws", her initials (all lowercase). Pam's password is left visible in these examples to illustrate the correct response to the login password request.

5. This message tells you how much time you are guaranteed on the system during this login session; after the stated time (here it is 10:07 am), you may occasionally be logged out (with advance warning), but usually you have as much time as you want. This line also serves as acknowledgment of a successful login.

6. Your User_id and the date, time, day and location of your current login session are listed.

7. The date, time, day and location of your last login session are listed. You can use this information to detect unauthorized use of your User_id and Person_id and Project_id. Multics will also inform you here of any unsuccessful attempts to log in using your Person_id and Project_id (including your own attempts, if you misspell your password).

8. The last line is a ready message. Included in this is the current time of day (on a 24-hour clock), and other information that reflects your use of system resources. The ready message appears when you are at command level: whenever Multics is ready to receive another command from you.

Now you are ready to begin working on Multics.

It is possible that the first time you type the login command line, you will not receive the prompting message "Password:". In fact, almost nothing will happen: your carriage (or cursor, the white square or blinking underscore on video terminals) moves over to the beginning of the login line without moving down to the next line. In this case, also press the LF (or LINEFEED) key. After you receive the prompting message and type your password, press both the RETURN and the LF keys again. When you receive the ready message from Multics, type:

set_tty -modes lfecho,crecho

and both the RETURN key and the LF key. From now until you log out, you can type just the RETURN key to send your command lines to Multics.

You will learn more about the set_tty command in Part 2, but for now, if you do not want to type this command line every time you. log in, ask your project administrator to make your RETURN key include a line feed permanently. (You can also do this yourself after reading the "exec_com" section in Part 2.)

If you make a mistake while logging in, and you have already typed RETURN without using the erase or kill characters, Multics tells you by printing an error message, and asks you to try again. Several error messages are shown in this section. Multics sends you an error message whenever you send it a line that it cannot process, because of incorrect format or inadequate information. No harm has occurred when you receive an error message; check your command line and try it again.

Here is an example of a typing mistake (Psissle rather than PSissle) on the command line:

Although the error was on the first line, Multics checked for a matching password before sending an error message. When you try again, start with the login command line.

Typing mistakes are the most common errors. It is important to type words exactly as they are indicated, with attention to both uppercase and lowercase letters (Multics distinguishes between uppercase and lowercase).

Here is another example, in which Pam forgot the space after the command:

Another easy mistake to make is to type your password incorrectly. (It is also hard to correct a mistyped password using the erase character, because you cannot see what you typed.) Multics responds this way:

After you mistype your password, you must type the entire login sequence again, beginning with the login command.

Each site administrator sets a limit to the amount of time you have and the number of attempts you can make to log in during one session; you usually have about 6 minutes or 6 tries. When you have exceeded this limit, Multics tells you to hang up the telephone, because it is automatically breaking your terminal connection:

If you typed everything correctly but are still denied entrance to Multics, you may not be registered yet. Check with your project administrator if you think this is the case. There may be other reasons for denying you access, such as a system shutdown, for which you receive an explanatory message from Multics.

Logging Out

When you finish your work on Multics, wait for a ready message and type the logout command to break your terminal connection. Multics responds by printing your User_id, the date and time that you log out, and your total system resource usage. It then reminds you to hang up the telephone:

Do not hang up the telephone before Multics has logged out; wait for the word "hangup".

You should always log out, hang up the telephone, and turn off the terminal before leaving, to avoid wasting computer time and to allow others to use the terminal. If you do not log out, another person can issue commands that Multics will interpret as being from you. This activity is charged to you, and may also result in damage to your work.

Most commands are flexible, letting you vary the way the commands work. The command name specifies an action to be taken; to direct the action of the command, you supplement it with information by typing words called arguments after the command name. The different kinds of arguments are discussed fully in Section 3, but one kind is of special interest to you at this point: the control argument.

The control argument is distinguished from other kinds of arguments by the hyphen which always precedes it. It is used as an optional argument - one that you include on the command line if you want the variation it stands for. Both the login and the logout commands take control arguments. You are introduced to a few of the most useful ones here.

The most important control argument for the new user, used with the login command, is -change_password. As discussed above, it is very important that you be the only person who knows your password. Here is an example of how to change a password:

Your password must be 8 characters or fewer (with no blanks), You may change your password as often as you like, but do not choose a word that people are likely to guess, such as your initials or the name of a pet. Try not to forget the one you use, because there is no record of it available to any person. If you do forget it, you must contact your project administrator and request a new one.

Another useful control argument for the login command is -brief. If you use the terminal several times a day, you may not want to see the introductory information that follows receipt of your password (lines 5 through 7 in the first example). Here is an example of logging in using the -brief control argument:

The logout command also accepts a -brief control argument:

When used with the logout command, -brief suppresses the logout banner.

The -hold control argument to the logout command aids the person who uses your terminal after you. It retains the terminal connection after you have logged out, and prints the Multics banner in readiness for another person to log in:

You can include several control arguments with one command, as long as they are acceptable to the command and are typed after the command but on the same line. For example:

When you combine the two control arguments to the logout command, the results may surprise you. Here is the complete interaction, from ready message to new login - Pam is trying this out by logging in again:

The -brief control argument carries over into the new login session -- no banner is printed! You must still use the "login -brief" command line if you want the shortened version of your new login session, though. The only indication you have that Multics is ready for a new user is that Multics sends a blank line after it logs you out.

As you learn about more commands, read through the command descriptions (Appendix B) to find out about the control arguments available to you with each command.

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