Fundamentals of Computer Science I (CS151.02 2007S)

Laboratory: Getting Started in the MathLAN

This lab is also available in PDF.

Summary: This laboratory reviews some mechanics related to the use of the Computer Science Local-Area Network (MathLAN) for CSC151. Specifically, this lab discusses:

Please don't be intimidated! Although this lab contains many details which may seem overwhelming at first, these mechanics will become familiar rather quickly. Feel free to talk to the instructor or with a MathLAN User Consultant if you have questions or want additional help!

Logging In

Short Version

To use any of the computers in the MathLAN, one must log in, identifying oneself by giving a user name and a password. You will have received a MathLAN user name and password from the instructor if you did not already have one. If you have not received a MathLAN user name and password, or if you have forgotten either one, please tell your instructor.

When a MathLAN workstation is not in use, it will display a login screen with a space into which one can type one's user name and, later, one's password. (If the workstation's monitor is dark, move the mouse a bit and the login screen will appear.) To begin, move the mouse onto any part of the box containing the login box. Type in your user name, in lower-case letters, and press the <Enter> key. The login screen will be redrawn to acknowledge your user name and to ask for your password; type it into the space provided and press <Enter>. (Because no one else should see your password, it is not displayed on screen as you type it in.)

At this point, a computer program that is running on the workstation consults a table of valid user names and passwords. If it does not find the particular combination that you have supplied, it prints a brief message saying that the attempt to log in was unsuccessful and then returns to the login screen -- inviting you to try again. Consult the instructor or the system administrator if your attempts to log in are still unsuccessful.

The Linux/Gnome Window Environment

Short Version

Once you have logged in, a control panel will appear at the bottom of the screen. Some other windows also may be visible in other parts of your screen. All of these areas are managed by a special program, called a windowing system. On MathLAN, login chores and other administrivia are handled by a program or operating system, called Linux, and the windowing system is called Gnome.

Practice with a Terminal Window: Changing Your Password

Short Version

While we can run several programs directly, we will need to invoke others by name. The computer program that reads and responds to such invocations is called the shell, and your interactions with the shell takes place in a window generated by a program called a terminal emulator, or terminal for short.

You may already have a Terminal window on screen. If not, you can start one at any time by moving the pointer onto the small monitor icon at the bottom middle of the front panel, and clicking with the left mouse button. Shortly a window appears, displaying the shell prompt -- the name of the workstation on which the shell is running, followed by a percentage sign. This prompt indicates that the shell is ready to receive instructions.

You type in such instructions using the keyboard. Move the mouse pointer into the Terminal window and click the left mouse button to make the window active. Notice that the window frame changes color following the click, indicating that the window has become active.

To get rid of the Terminal window, press <Ctrl/D>. That is, hold down either of the keys marked <Ctrl>, just below the <Shift> keys, and simultaneously press the <D> key. (On our workstations' keyboards, the keys marked <Ctrl> (control) and <Alt> (alt or meta) are somewhat like <Shift> keys, in the sense that they modify the effect of other keys that are pressed simultaneously.) The shell program interprets <Ctrl/D> as a signal that you have no more instructions for it and halts, and the terminal emulator closes the window automatically once the shell stops running. Alternatively, you may close a window by moving the mouse to the x at the top-right of the window, and clicking the left mouse button. Finally, you can usually type exit to close a terminal window.

It is a good idea to change the password associated with your account shortly after you receive it and every few months thereafter. The program that one uses to change one's password is by its name, yppasswd.

Choose a new password. Make it something that you can easily remember, but not an English word or a name, since it is easy for system crackers to break in by guessing your password if you choose it from one of those categories.

Open a terminal window, select the window by clicking the left mouse button in it, and type the word yppasswd. The password program prompts you once for your old password -- the one you logged in with -- and twice for your new password. If you give your old password correctly and the two copies of your new password match, the program substitutes the new password for the old one in the table that the login program consults. The old password is discarded and will not be recognized in subsequent logins. (If the attempt to change the password fails for any reason, however, the old password is retained.)

A typical interaction to successfully change a password looks like this:

   bourbaki% yppasswd
   Changing NIS account information for user on
   Please enter old password:
   Changing NIS password for user on
   Please enter new password:
   Please retype new password:

   The NIS password has been changed on


After running the yppasswd program, the shell takes over again and issues another prompt. You can invoke as many programs as you like from the shell, one after another, before pressing <Ctrl/D> or exit to leave the shell.


Short Version

Almost all of the materials for this course will be distributed over the World Wide Web rather than in paper copies. To view materials, such as this course's syllabus and this lab, you may follow these steps:

First, prepare to use the World Wide Web by clicking on the Iceweasel icon (the picture with small white creature holding a green sphere). Iceweasel is a version of Mozilla Firefox renamed to accomodate trademark issues. More info on the relationship between Firefox and Iceweasel can be found at I will generally use the terms interchangably.

The first time you run Iceweasel on MathLAN, two message boxes might appear.

You should approve of any requests by clicking on the appropriate word. The pop-up boxes then disappear; you should not see them on subsequent uses of Iceweasel.

Initially, Iceweasel displays a World Wide Web document containing some default information. You should switch to the page, which is an entry point to the Computer Science Department's Web site.

I expect that most of your are already familiar with a Web browser. If not, please consult with me or one of your colleagues.

To find material for this course, scroll down the origin page for the Computer Science Department to the list of course front doors. Now scroll down this page to find the entry for this course, Fundamentals of Computer Science I, Section21, and click on it to locate the front door for this course. Next, click on the Syllabus link to view the current draft of the semester's schedule. If you click on the Current link, you'll see an outline of today's class.

You can also connect to the Web page for this class by selecting Open Web Location from the File menu and then entering

Iceweasel Options

Short Version

Each MathLAN user can configure Iceweasel to reflect her or his own preferences. Between logins, these preferences are stored in a file in the user's home directory; when Iceweasel is started during a later session, they are reinstated from that file.

Every user of Iceweasel on MathLAN should establish a base page, a starting point for browsing. Here are the Uniform Resource Locators or URLs of some good choices:

To establish your base page, within Iceweasel, bring up the Edit menu from the menu bar and select the Preferences operation. A pop-up window appears, allowing you to configure many features of the general appearance of Icewesael. Choose the General option, if it has not been chosen already. The rectangle labeled Home Page contains the URL of some document that serves as the default. Replace the contents of this rectangle with the URL of your choice. (This does not have to be a permanent change; you can change your mind about this configuration at any time within Iceweasel.)

To erase the current contents of the Home Page Location(s) box, move the mouse pointer to the left of the first character in the box, press the left mouse button and hold it down, and drag the mouse pointer rightwards until the entire URL is displayed in reverse video, white letters on a black background. Then release the left mouse button and type the new URL; the old one will vanish as soon as you start typing. Once you have entered the new URL, move the mouse pointer onto the button marked OK at the bottom of the pop-up window and click on it with the left mouse button.

You can, of course, simply navigate to the page you want to use as your home page and then click on Use Current Pages.

You may note that the button says Pages (plural) rather than Page (singular). Since Iceweaselpermits tabbed browsing (that is, you can have tabs within the same window that you switch between), you can have a home set of tabs. Particularly obsessive people might want to set up a sequence of tabs with say, the current outline, the current eboard, the current reading, the current lab, and Plans (for when you get bored).

Using Icedove/Thunderbird for Email

While you probably use Microsoft Outlook Web Access for most of your email, you can also use Thunderbird, which works well on Linux, Macintosh, and even Microsoft Windows (at least when it's configured right). In MathLAN, Thunderbird is called Icedove, for similar trademark reasons to those described above for Firefox and Iceweasel. So that you can send email appropriately within the MathLAN, I'd like you to configure Icedove as a mail client. Most importantly, Icedove lets you use the mailto links that sometimes appear in pages.

Adding an Icon to the Task Bar

Your first task in getting Icedove running correctly is to add a Icedove icon to the task bar. (Almost as importantly, once you figure out how to add an icedove icon, you will also be able to add other applications that you want to use.)

Short Version

If you've done everything to the satisfaction of the computer (and, as you recall, computers like to misinterpret what you've asked, so they can be hard to satisfy), you should now have an icon for Icedove in your task bar. If you don't, please obtain help from a teacher or teaching assistant.

Finally, click on the icon to start Icedove.

Warning: For unknown reasons, Icedove currently seems to take an insanely long time to start.

Configuring Icedove

You'd hope that you could now read mail, wouldn't you? However, Icedove needs to know which email account to use. Hence, you need to answer a series of questions.

Icedove may ask whether it should import information from some other email package. Tell it not to. If all goes well, it will then prompt you to set up a new account. You will be setting up an Email account. Please use your name and your Grinnell email address for the Identity.

In the Server Information dialog box, select IMAP, use as the incoming server, and use as the outgoing server, too.

Getting Mail

Once you've configured Icedove, you should be able to read your Grinnell College email. Spend a few minutes getting acclimated to Icedove. Try to send at least one message (e.g., to me). Send a message to yourself that includes a URL (e.g., The CSC151 site is I can't believe that Rebelsky uses such long URLs.)

Spend no more than five minutes reading email. (And no, don't tell all your friends My assignment in 151 was to read email.)

Making Iceweasel and Icedove Play Together

Unfortunately, even though Iceweasel and Icedove were written by the same people, Iceweasel thinks it should launch a different mail reader when you try to send mail or click on a mailto link, and Icedove thinks it should launch a Web browser other than Iceweasel. (Just remember, Sentient and Malicious.) Hence, you need to teach them about each other. (Don't worry; if everything goes well, you'll never have to do it again, at least not this semester.)

Using Icedove for Mail Links

Let's starting by making Iceweasel use Icedove to send mail.

Short Version

I should insert a long discussion here to match the structure of the other sections, but I'm feeling lazy right now. Suffice to say, there are lots of silly things going on, but there's no real intellectual benefit in learning about this stuff (at least not at this stage of your career).

Using Iceweasel for URLs in Mail

Let's continue by making Icedove use Iceweasal to open URLs. These steps, believe it or not, are even more convoluted than those you did above. (No, you may not tell your friends I spent all of CSC151 following stupid and unexplained instructions that did nothing more than configure my Web browser and mail reader to work correctly.)

Short Version

Believe it or not, but all that you accomplished with those steps is to make Icedove let you configure it. Let's hear it for sensible design.

The short version was so long that there is no way that I'm going to write a longer, narrative version, at least not in the near future.

Finishing Up and Logging Out

If you've successfully logged in, changed your password, started Iceweasel, selected your base page, started Icedove, made Iceweasel and Icedove play together, and sent me some email, you've completed the lab and you can finally stop.

Short Version

When you are done using a workstation, you must log out in order to allow other people to use it. To log out, move the pointer onto the menu icon near the left of the front panel, click the left mouse button, and select the Log out option. A confirmation box will pop up, asking you to verify that you're ready to log out; move the pointer onto the word Yes near the bottom of this box and click the left mouse button. The Gnome windowing system vanishes, and after a few seconds the login screen reappears; this confirms that you're really logged out.

Please do not turn off the workstation when you are finished. MathLAN workstations are designed to operate continuously; turning them off and on frequently actually shortens their life expectancy.




Disclaimer: I usually create these pages on the fly, which means that I rarely proofread them and they may contain bad grammar and incorrect details. It also means that I tend to update them regularly (see the history for more details). Feel free to contact me with any suggestions for changes.

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Samuel A. Rebelsky,

Copyright © 2007 Samuel A. Rebelsky. This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.