An Algorithmic and Social Introduction to Computer Science (CSC-105 2000S)


Getting Started in the MathLAN

Goals: This lab reviews some mechanics related to the use of the Mathematics Local-Area Network (MathLAN) for CSC105. Specifically, this lab discusses:

Logging In

To use any of the computers in the Mathematics Local-Area Network, 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 the instructor.

When it is not in use, a MathLAN workstation displays 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, press the <Shift> key or move the mouse and the login screen will appear.) Typically, this space is outlined in red; this means that it is ready to receive a user name. 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 pops up a message box saying that the attempt to log in was unsuccessful and inviting you to try again. Press the <Enter> key to dismiss the message and re-enter your user name and password. Consult the instructor or the system administrator if your attempts to log in are still unsuccessful.

The Common Desktop Environment

When the login program has validated your user name and password, it activates a user interface, a program through which one manages various programs and resources that the workstation can access. (Our user interface is called the Common Desktop Environment, or CDE.) It takes a few seconds to prepare this interface; during this short period of preparation, the workstation displays a blue transition screen.

When CDE takes over, you see at the bottom of the screen a front panel decorated with a variety of icons. You can use most of these icons to activate computer programs. Moving the mouse around on its pad causes a mouse-controlled pointer to move around in a corresponding way on the screen. If one places this pointer on top of one of the icons and clicks on the leftmost of the three buttons on the mouse (pressing and releasing it immediately), the program represented by the icon starts to run.

The programs that you start in this way display their output in windows -- rectangles drawn onto the screen, superimposed on the pastel background. (One such window, labeled dtterm, appears automatically the first time you log in. We'll discuss dtterm shortly.) Each window is enclosed in a frame drawn in one of two contrasting colors, depending on whether or not the window is active: at any given moment, the active window is the one to which anything the user types will be directed. A window becomes active when you move the pointer to some exposed point inside the boundary of the window frame.

If you want to set a window aside for the moment, with the possibility of returning to it later, look closely at the upper right-hand corner of the window, where the frame contains a small square with a dot in it. If you move the pointer into that square and click on the left mouse button, you minimize the window, closing it up into a small rectangular icon along the left-hand edge of the screen. A minimized window can be restored by moving the pointer onto its icon and clicking the left mouse button twice in rapid succession.

Netscape Navigator

Many 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:

The Course Web

As you will soon notice, the top and bottom of each page in the course Web are always the same. The top contains the name of the course and links to various components. The bottom contains the links and some supplementary information. Whenever you click on the course name at the top, you return to the Front Door for the page.

Click on ``Search'' (near the top of the page). You should see a screen in which you may type a term. Type ``MathLAN'' and then hit the ``Enter'' key. You should see a list of course documents that pertain to the MathLAN (primarily this document, but also others). Click on one of the documents in the list and see what happens.

Click on the course name at the top of the page. Verify that you return to the Front Door for this course.

Click on ``Current'' and you should see the outline of today's class. It will mention this lab and the many other things we have planned for today's class.

Spend about five minutes visiting other links so that you can begin to understand what is in the course Web.

Netscape Navigator Options

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

Every user of Netscape Navigator on MathLAN should at some point perform two specific configuration steps:

Base Page

To establish your base page, within Netscape, 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 Netscape Navigator. Choose the Navigator option. The rectangle labeled Home Page Location contains the URL of the ``Welcome to Netscape'' document at Netscape Communications Corporation; this is what Netscape Navigator uses by default as a base page. Replace the contents of this rectangle with one of the URLs shown above. (This does not have to be a permanent change; you can change your mind about this configuration at any time within Netscape Navigator.)

To erase the current contents of the Home Page Location 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.

Here are the Uniform Resource Locators or URLs of some good choices:

You may also wish to create your own starting page (and will have the resources to do so in a few days).

Disk Cache

To reduce the size of the disk cache, bring up the Edit menu again and select the Preferences operation. Again a pop-up window appears. Click on the right-pointing triangle next to Advanced and then click on the Cache option. Erase the number (typically 5000) that appears in the rectangle labeled Disk Cache and replace it with 0. Finally, click on the OK button at the bottom of the pop-up window.

The dtterm terminal emulator

While one can perform many tasks on our Unix workstations using the convenient icons on the front panel, some tasks must be entered at a command-line prompt. That is, to run some programs, one must invoke them by name. The computer program that reads and responds to such invocations is called the shell, and one's interactions with the shell take place in a window generated by a program called a terminal emulator. The particular terminal emulator that we shall use is named dtterm.

You may already have a dtterm window on screen. If not, you can start one at any time by moving the pointer onto the small monitor-and-keyboard icon, fourth from the right on the front panel, and click with the left mouse button. Shortly a window will appear, 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.

One types in such instructions using the keyboard. Move the mouse pointer into the dtterm window to make it active. Notice that the window frame changes color when the pointer crosses it, indicating that the window has become active.

To shut down dtterm, 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 dtterm terminal emulator closes the window automatically once the shell stops running.

Practice with dtterm: Changing your password

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 also invoked by its name, password.

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 dtterm window, move the pointer into it, and type the word password. The password program will prompt 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 will substitute the new password for the old one in the table that the login program consults. The old password will be discarded and will not be recognized in subsequent logins. (If the attempt to change the password fails for any reason, however, the old password will be retained.)

After running the password 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> to leave the shell.

Editing

There are a number of different text editors available in the MathLAN. Text editors are computer programs that are intended to help you create files that contain normal characters - papers, programs, Web pages, etc. Unlike word processors---which give you control over font color, layout, and such---text editors focus on text and not on appearance.

In this class, you will use one of the simplest text editors available on our system: dtpad. Those of you taking CSC151 will use another text editor, emacs. For now, everyone should start with dtpad.

In a dtterm window, type dtpad followed by ``Enter''. In a few seconds, a new window should appear on the screen. In that window, type your name, a blank line, and your answer to today's question (What computing knowledge do you hope to get from this course?). For example,

Samuel A. Rebelsky
CSC105
Question 2: What computing knowledge do you hope to get from this course?

I hope to learn how non-computer scientists react to a number
of issues in computing, particularly the design of algorithms
and programming.  I also hope to expand my own sense of the
implications of computing.

Click with the left mouse button on the word ``File'' at the top of the window. As you may have guessed, this is a menu. Next, click on ``Save''. You will then see a fairly complicated dialog box. Type in a name for the file (perhaps answer.02) and then click with the left mouse button on ``OK''. You have now saved the file.

Printing

There are a number of ways to print your documents. The easiest way to print a document is from an application. Most applications (including dtpad) let you select ``Print'' from some menu (in dtpad's case, the ``File'' menu).

If you don't feel like starting the application, you can also print many files directly from the dtterm window. You simply type

% lp file

(Do not type the percent sign, and fill in the name of the file). The ``lp'' stands for ``line printer''. In the MathLAN, one advantage of using lp is that you can more easily change some settings. For example, to print a longer paper on both sides of a page, you can type

% lp -oduplex file

Print one copy of your answer to question 2.

Sending Email in the MathLAN

When you create files in the MathLAN, you'll need a way to send them to me (and to yourself on other computers). I recommend that you use an email program. I don't use WebMail, so I'll admit that I don't know about the capabilities of WebMail.

The easiest way to email a file in the MathLAN is to open a dtterm window and type

% elm -s "Subject" recipient < file

For example,

% elm -s "Question 2" rebelsky@grinnell.edu < answer.2

Note that you shoujld always use the @grinnell.edu form for email addresses.

The MathLAN has a separate email system. Hence, you might get MathLAN email that you won't see in WebMail. To read your MathLAN email, click on the letter tray you see in your front panel. You can tell that you have mail when the letter is turned on its side.

Closing Up/Logging Out

If you've successfully logged in, started up and shut down dtterm, changed your password, started Netscape Navigator, explored the course web, selected your base page, reduced the Netscape Navigator disk cache to zero, exited from Netscape, created a file, printed that file, and logged out, you've completed the lab for today.

You may be wondering about that last step. When one is done using a workstation, one must log out in order to allow other people to use it. To log out, move the pointer onto the EXIT icon near the middle of the front panel and click the left mouse button. A confirmation box will pop up, asking you to verify that you're ready to log out; move the pointer onto the word OK near the bottom of this box and click the left mouse button. CDE vanishes, and after a few seconds the login screen reappears; this confirms that you're really logged out.

It is not necessary to 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.


created December 29, 1996 by John David Stone
revised August 21, 1999 by Henry M. Walker
revised August 24, 1999 for use in tutorial by Sam Rebelsky revised January 24, 2000 for use in CSC105 by Sam Rebelsky (added section on email; changed a few examples and comments)


Disclaimer Often, these pages were created "on the fly" with little, if any, proofreading. Any or all of the information on the pages may be incorrect. Please contact me if you notice errors.

This page may be found at http://www.math.grin.edu/~rebelsky/Courses/CS105/2000S/Labs/mathlan.html

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