Laboratory: Getting Started with Linux

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

When a Linux 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.) This window belongs to xdm, the Xwindows Display Manager.

Before you log in, you should specify which window manager you want to use. Find the drop-down menu labeled Default Xsession. Click the triangle for the drop-down menu and choose Xfce session instead. move the mouse. In the future, xdm will remember Xfce as your preferred default, so you will not need to do this again.

Now, move the pointer 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.)

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.

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 window manager. On our network, login chores and other administrivia are handled by a program or operating system, called Linux, and the primary user interaction is handled by a window manager, called Xfce.

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, look for an icon of a computer monitor near the lower-left corner of the screen. If you see this icon, move the pointer over the icon and click the left mouse button once to launch the Terminal.

If you do not see a Terminal icon, then move the pointer onto the applications menu icon at the bottom left of the panel (in Xfce, it looks like a creature on a blue X) and click once with the left mouse button. The applications menu will pop up. Move the mouse over System, then Terminal Click the left mouse button once to launch the Terminal.

In the terminal window, you will see a shell prompt -- the name of the workstation on which the shell is running, followed by a dollar 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 “passphrase”.

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. We'd also recommend that you choose a password of more than eight characters (a few words can be good - spaces are allowed).

Open a terminal window, select the window by clicking the left mouse button in it, and type the word passphrase. The password program prompts you once for your old password -- the one you logged in with -- and twice for your new password. Note that nothing will appear when you type your password. To ensure that no one eavesdrops on your password (or even the length of your password), the workstation leaves the cursor in place while you are typing passwords.

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$ passphrase
Changing NIS account information for user on hurd.cs.grinnell.edu.
Please enter old password:
Changing NIS password for user on hurd.cs.grinnell.edu.
Please enter new password:
Please retype new password:

The NIS password has been changed on hurd.cs.grinnell.edu.

bourbaki$ 

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 or exit to leave the shell.

While some materials for this course will be available in paper, almost everything for this course (including electronic versions of paper materials) will be available on the World Wide Web. In this class, we use a version of the Firefox browser called Iceweasel. Almost all of the materials for this course will be distributed over the Web. To use Iceweasel 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 purple sphere). Iceweasel is a version of Mozilla Firefox renamed to accommodate trademark issues. More info on the relationship between Firefox and Iceweasel can be found at http://en.wikipedia.org/wiki/Naming_conflict_between_Debian_and_Mozilla. We will generally use the names interchangeably.

If you do not see the Iceweasel icon, then move the pointer onto the applications menu icon at the bottom left of the panel (in Xfce, it looks like a creature on a blue X) and click once with the left mouse button. The applications menu will pop up. Move the mouse over Internet, then Iceweasel Click the left mouse button once to launch Iceweasel.

The first time you run Iceweasel on our network, 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 http://www.cs.grinnell.edu, which is an entry point to the Computer Science Department's Web site.

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

To find material for this course, click on the “Curriculum” link in the menu on the left side. A new link for “Current courses” should appear. Click that. Find the entry for this course, Functional Problem-Solving, Section 01, and click on it to locate the front door for this course. Next, click on the Schedule link to view the current draft of the semester's schedule.

You can also connect to the Web page for this class by selecting Open Web Location from the File menu and then entering http://www.cs.grinnell.edu/~rebelsky/Courses/CSC151/2014F/.

As you may know, there has been a rise in malicious programs (scripts) that reside on Web pages. For that reason, our system administrator has installed the NoScript plug-in which, by default, disallows scripts from every site.

However, many common services on campus, including Outlook Web Access and PioneerWeb, rely on scripts. Hence, we recommend that you enable scripting for sites in the grinnell.edu domain.

Most user interface systems provide a convenient way to access commonly-used applications. In Xfce, we often add such applications to the panel. To add an application launcher to the panel, we can drag it from the applications menu into the panel. (There are also other ways to add application launchers to the panel, but this is the easiest one.)

Of course, you should make sure that all of that worked. Click on the GIMP icon to see if the application starts. Then quit.

If you want to put the GIMP launcher in a different place on the task bar, you can right-click on the icon to move it.

In the toolbar at the bottom of the screen, you should see an icon that looks like a box containing four smaller boxes. (If you don't see it, ask for help.) This is the workspace switcher, a tool that lets you keep your application windows on several different desktops or workspaces.

The upper-left-hand box represents the desktop you are working on right now. It contains a number of still smaller boxes of varying shapes and sizes, which represent the windows you have open. When you move or resize the a window on the desktop, you should see the window's representation in the switcher move as well. Give it a try by wiggling one of your windows around.

Now, click in one of the other three boxes. You should see a new, blank desktop with no windows on it. Where did they go? If you look at the switcher, you'll see they are still in the desktop you started on. Switch back to that desktop.

You can also use the switcher to move windows from one desktop to another. Find the switcher again and identify the box that corresponds to your Iceweasel/Firefox window. Click that box and drag it a little ways to the right, onto the next desktop. The window should disappear from the first desktop. If you click onto the desktop to the right, you should see it there.

In this class, you'll usually need to work with multiple windows: The DrRacket window for your programs, various GIMP windows containing tools and images, and a web browser to read the laboratory exercises and reference materials. As you get settled in over the next few weeks, consider how you might use the switcher to help you organize your workspace efficiently.

By default, the workspace switcher presents four workspaces arranged in two rows of two each. If you want to change this configuration, right-click on the workspace switcher and select Properties to change the number of rows. Clicking on Workspace settings... will let you change the number of workspaces.

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 your username, at the lower right corner of the screen, and click the left mouse button. A menu will pop up giving several options. Move the pointer onto the words Log Out at the bottom of the menu and click the left mouse button. A confirmation dialog will appear, giving you 30 seconds to change your mind. Click the Log out to log out immediately. The Xfce window manager 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. The Linux workstations are designed to operate continuously; turning them off and on frequently actually shortens their life expectancy. We are working on finding ways to ensure that their power consumption is low when they are on but unused.