Problem Solving and Computing (CSC-103 98S)

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Getting Started in the MathLAN

[Significant portions of this document are by John David Stone and are taken from the document at url ]


One of the first hurdles you must clear in order to do the work in the class is to log in to the MathLAN computers (the HP workstations). We'll be using these computers to run Netscape Navigator and various programming utilities.

First, you need to get a MathLAN account and password. Your account will have the same name as your vax account. However, the MathLAN accounts are administered separately and have separate passwords. If you were pre-registered for the course, I've tried to make sure you have an account. If you were not pre-registered for the course, work with someone else today and talk to me about getting an account. I will hand out sheets with passwords.

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.

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.

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.

CDE Basics

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. Note that you should only click once on an icon.

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, labelled 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.

Logging Out

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. In fact, you should never turn off the workstations. MathLAN workstations are designed to operate continuously; turning them off and on frequently actually shortens their life expectancy.

The dtterm terminal emulator

Many of the programs that we use in this course are not represented by icons on the front panel. To use these programs, we 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 an 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.

Netscape Navigator

Many of the handouts and other materials for this course will be distributed over the World-Wide Web rather than in paper copies. One can display World Wide Web documents in a window on a MathLAN workstation by invoking the Netscape Navigator program. To run Netscape Navigator, move the pointer onto the ``walking N'' icon near the middle of the front panel and click the left mouse button.

The first time you run Netscape Navigator on MathLAN, two message boxes pop up. One of them asks you to consent to the terms of Netscape Communications Corporation's licensing agreement; the other requests permission to create some configuration files in your home directory. It's all right to approve both of these requests by clicking on the appropriate word. The pop-up boxes then disappear; you won't see them on subsequent uses of Netscape Navigator.

Initially, Netscape Navigator displays a World Wide Web document containing its logo, version number, copyright notice, and such like. After a minute or so, or sooner if you click inside its window, the program replaces this document with a startup page entitled ``The origin,'' which is an entry point to the Mathematics and Computer Science Department's web site.

To shut down Netscape Navigator, move the mouse pointer on top of the word File in the upper left-hand corner of the window, on the menu bar. Press and hold down the left mouse button. A list of operations appears, and the Exit operation is at the bottom of this list. Still holding down the left mouse button, move the mouse pointer on top of the word Exit, then release the mouse button.

URLs and bookmarks

Netscape Navigator can display any document on the World Wide Web. One way to refer to such a document is to give its Uniform Resource Identifier, or URL, which is a kind of address by which Netscape Navigator can locate and request the document.

To direct Netscape Navigator to load a document for which you know the URL, bring up the File menu again and select the Open Page... operation. A dialogue box pops up; move the mouse pointer into the long rectangle in the center of this box, click with the left mouse button, type the URL into the rectangle, and press the <Enter> key at the end. The dialogue box disappears and Netscape Navigator loads the requested document.

Because URLs are notoriously hard to remember and to type accurately, Netscape Navigator allows you to place a bookmark on any interesting or important document that you reach. To place a bookmark on the document currently displayed, move the mouse pointer onto the word Bookmarks just above the main display window, press and hold the left mouse button to bring up the corresponding menu, and select the Add Bookmark operation. You can subsequently return to that document by bringing up the Bookmarks menu again and selecting from it the title of the document.

Netscape Navigator options

Each MathLAN user can configure Netscape Navigator to reflect his or her 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 MathLAN user should reduce the disk cache to zero. (The disk cache is a collection of files, stored in your account, containing copies of recently examined documents and graphics. MathLAN does not have enough disk space to allow all users to maintain large disk caches, and they have little effect on the performance of Netscape Navigator in most cases.)

To reduce the size of the disk cache, bring up the Edit menu again and again select the Preferences ... operation. When the Preferences window appears, click on the small rightwards-pointing triangle to the left of the word Advanced in the list of customization categories, then on the word Cache that appears underneath it. Erase the number (typically 5000) that appears in the box labelled Disk cache and replace it with 0. Finally, click on the OK button at the bottom of the pop-up window.

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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.

Source text last modified Tue Jan 20 12:10:28 1998.

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