Lab 0: Introduction to Linux and Firefox

Getting started with Linux:

The computers in the 2nd floor MCSP lab are dual boot, capable of running Windows 7 or Ubuntu Linux, an open source version of Linux. Generally you will find them running Windows so you will need to reboot into Linux as follows:

• Press CTRL-ALT-DELETE, click the red dislosure triangle button in the lower right, then select Restart from the pull down menu.
• Watch the screen! It does a few things and then displays the bootloader screen (LILO), with a menu asking which operating system to load. Use the arrow keys to highlight Ubuntu Linux, then press ENTER. (If you wait too long, Windows 7 will automatically be loaded!)

After Linux has been loaded you should get a login screen. To log in, click the "Log In" button, enter your username and password (the same that you use to access my.roanoke and email). If you ever have password problems, go to Information Technology on 3rd floor Trexler for assistance. You are now logged into the local machine, but you will be storing your files and running programs from a remote computer (named "CS"). This means that you can use any computer in the lab and still be able to access your personal files.

You should see a desktop environment similar to Windows. This is GNOME which is responsible for providing a graphical, desktop interface for Linux. Here are some of the basics for getting around in Gnome.

• The bar across the top of the screen is the GNOME Panel. Just as you access programs in Windows from the Start menu, you can access programs in GNOME by selecting the appropriate menu options on the GNOME Panel. You should also see two color icons on the left side of the panel - one for the Firefox Web browser and one for GNOME Help. You can hold your mouse over an icon to get information about it.
• A taskbar is at the bottom of the screen. It contains an icon for each window that you have open on the desktop. These are similar to the icons that you see on the taskbar in Windows.

The GNOME panel can be customized by adding and deleting icons and moving them around. In this course we will regularly use three applications: Terminal (for typing in shell commands), Emacs (a text editor for writing programs), and Firefox (for an online copy of lab instructions). It would be helpful to add icons for these on the panel.

• Add an icon for Terminal to the panel by clicking on the "Applications" menu option, then choosing Accessories. Right click on Terminal and choose "Add this launcher to panel."


• A similar process can be used to add an icon for the text editor "GNU Emacs 23". (Also under Applications, Accesories)


• If you ever wish to remove an icon from the panel, right click on the icon then choose "Remove from Panel."

Now open Firefox using the icon on the panel.

You should now have two windows open. You can use the mouse to move and manipulate these windows and open programs in the same way you do in other GUI environments that you are familiar with. As in other systems you can also use key strokes to do many of the same things and often that is faster. Here are a couple you may find useful.

1. Moving Windows: As usual, windows can be moved by dragging the title bar but an alternative is to hold down ALT and then click anywhere in the window to drag it to a new location. This is particularly handy if the title bar is not visible.

2. Activating a Window: Clicking inside a window or on its titlebar both activates the window and brings it to the front. When you have more than one window open it is often helpful to cycle through them to get to the one you want to work in. The usual way to cycle through windows in GNOME is by pressing Alt-Tab (hold Alt down, then press Tab), just as in Windows. Now try ALT-Tab; it should cycle through the windows.

Setting up Firefox

Firefox is an open-source web browser that looks and acts much like Internet Explorer, Safari, or Google Chrome. Open Firefox by clicking on the icon on the panel. First, we want to set the class webpage to be your homepage. Under the Edit menu, select Preferences. The preferences dialog will open, and you should see a textbox for Home Page.

If you are in Dr Ingram's class, type in:

 
http://cs.roanoke.edu/~cpsc/Fall2010/CPSC120A 

 
http://cs.roanoke.edu/~cpsc/Fall2010/CPSC120B 

Using the Command Line Interface

While pointing and clicking is familiar and fairly intuitive, it is not always the most efficient way to give commands when working with a computer. For this reason, many computer users, especially programmers, prefer to interact with the computer system by typing in commands that explicitly tell the machine what to do. The command-line interface for Linux systems is accessed through an X-terminal(xterm).

Activate the xterm you already have open. The program running in the xterm is called the shell. The shell lets you issue commands explicilty to the Linux operating system and work with files. The following leads you through using some of the basic commands in Linux. Refer to the Linux Command Reference and Linux/Unix Overview handouts given in class as you answer the following questions and type in the appropriate commands to move around the file system. Pay attention to what happens on the screen after each command.

1. How do you find out "where you are" in the file system? The command is pwd which stands for present working directory. To find out where you are now type pwd

   What is displayed when you type in the command (and press ENTER)?

   ___________________________________________________
   (Note - this should be the full pathname of your home directory - you are always in your home directory when you first log in.)

2. How do you change to another directory?

   The command is cd (for change directory) BUT you must also type in an argument specifying the directory you want to change to (give either an absolute or relative path to the directory). Note that for any Linux command with an argument you must type a space between the command and the argument.

   Let’s go to the root directory (also known as “/”).
   To do so, you need to type
   

    
                   cd  /
   

3. How do you see what files are in a directory?

   The command to see the files in your current directory is ls. To see a list of files in a different directory you need to add a pathname to that directory as an argument.

   Look at the files that are in the root directory (that's where you are!) by typing the ls command.  

   You should see quite a few files including one named etc. It is one of the system directories mentioned in the Linux/Unix Overview handout. Now do the following:

   • Change to the etc directory (remember you need to use the cd command AND give the pathname of the directory you want to change into).

   • Type the command to see what is in the etc subdirectory.

4. How do I get more information about the files?

   Use the -l option on the ls command; that is, type ls -l (that is an el for long, not a one) to get a long listing of the files.    Type the command to see info about the files in the etc directory. Note that this shows you the permissions on each file (described on the last page of the Linux/Unix Overview), the ownership and group for the file (most of these are root), the size of the file (number of bytes), and the date of last modification of the file.

   Note that some of the filenames show up blue and some are black (you will see two more colors if you scroll up - green and light blue). The file permissions are displayed in the first column (this is the sequence of 10 characters described on page 3 of the Linux/Unix Overview handout). What do you notice about the permissions on the blue files versus the black ones?
   

5. Now change to the “bin” directory. Recall that bin is a subdirectory of root – but we are now down one level in etc (see diagram on page 2 of the Linux/Unix Overview). So we can change to root in one of several ways:
   • In two steps - go up one level to root by typing cd .. (remember .. is the directory up one level from where you are), followed by typing cd bin.
   • In one step with the relative pathname of bin - type cd ../bin
   • In one step using the full pathname from the root - type cd /bin

   Now type the command to list the files in bin.   Note that a lot of the files contained in this directory are displayed in green.   You may also notice some familiar file names (cp, ls, pwd, for example).  

   Type ls –l and examine the permissions on the green files. What are the permissions for all users?
     What do these (green) files all have in common?   

   
   

6. How do you find permissions for a specific file?

   To do this we need to add the filename as an argument to the ls command. For example to see the permissions on the file cp type:

    
                 ls -l cp
   

   Make a note of what happens (especially the permissions).

7. How do I go back to my home directory?  

   This is an example of changing directory so you need to use the cd command. As before you could use it with an argument that gives the pathname of your home directory. However, the fastest way to change to your home directory, is to just type cd

   Other options include:
   
   

   • cd ../home/students/username takes into account your current location.  Effectively this will take you back up one directory, and then down through home/students
   • cd /home/students/username specifies the absolute path that you want to jump to
   • Since you are going to the home directory of a user, you can just type cd ~username
   (of course put your username here)

Setting Up Your Directory

Now we'll set up your directory with some subdirectories and copy some files into them. Do the following:

• Use the appropriate Linux command to see what is currently in your directory (you should see one file named “Desktop” and one named “Documents” among others). What type of files are these? (Look at the file type information from the ls -l command.)
• It turns out there are some other files there. These hidden files are not always displayed (because you don’t need them all on a regular basis). How do you list all of the files in your directory? (Look at the Linux Command Reference for options on the ls command)
  
Notice that all the “hidden” files start with a “.” – these are created by the system.



• You need to create (make) a new subdirectory, named cs120, to store your files for this class. Look at the command reference to figure out the command to do this. Please note!!! Linux is case-sensitive; the directory cs120 is NOT the same as CS120. It is very important in this class that you type in commands, pathnames and filenames in the correct case!
  List the files now in your directory to be sure you now have the cs120 subdirectory.
  
  
• Change directories to the new subdirectory and confirm that you are there.
(You can use pwd to confirm, but you may notice that your current directory is also displayed as part of your prompt.)


• Create a new subdirectory named labs and change to this directory.
• Create a new subdirectory called lab0 and again change to this directory.
• Now we want to copy a file called UnixQuestions from the cpsc home directory to your present directory. The shell command you need to type must specifiy three pieces of information:
  • The command itself which is cp (for copy) PLUS two arguments - one the file you are copying and the other telling the operating system where to put the copy. See the examples in the Linux Command Reference.

    Note that we need the pathname for the original file (the one we want to copy) and the directory (or file) we want to put it in. The pathname of the file we want to copy is ~cpsc/UnixQuestions (because the file is in the home directory of "user" cpsc).

    We want to put the file in the directory we are currently in. Remember that you can refer to your current location as “.” - that is, a single dot.

  So, the command is

   
      cp ~cpsc/UnixQuestions .
  

  
  
• Confirm the file is in your directory with ls.

• Go back to the cs120 directory by going up the tree (remember the directory up one level is referred to using two dots so changing up one level is cd ..). You should have only one subdirectory of cs120 at this point (labs).   Create another subdirectory called assignments     We will use this directory later in the term.
  

STOP!!! Before going further have the instructor or a lab assistant come over and check to see that you have your directory set up correctly. You will be asked to go to your home directory, show a listing of the files there, then go down into the subdirectories you have created and show what is there.

Using Emacs, the Text Editor:

Editing an existing file

We'll first use Emacs to edit the UnixQuestions file. To open this file in your lab0 subdirectory do the following:

• In your Emacs window, use the pull down menu item Open File... under the File menu, or use the key stroke C-x C-f   (the C stands for the Control ctrl key -- hold it down then press the x key, release the x then press the f).
• Look at the bottom of the window in the minibuffer and you will see the words Find File: followed by the path of the directory you were in when you started Emacs (probably "~/", that is, your home directory). You need to specify the path for the file you want to open to edit. If you have correctly created your subdirectories, the file should be in ~/cs120/labs/lab0/UnixQuestions. (Remember that this is the same as /home/students/yourUsername/cs120/labs/lab0/UnixQuestions because ~ stands for your home directory.) Type this into the minibuffer (don't type the ~/ again if it's already there) and press ENTER and you'll be in a buffer containing the file. The file name corresponding to the buffer will appear near the bottom of the window on the status line.

A useful Emacs command: If you ever get stuck halfway into an Emacs command, where the minibuffer is asking for something that you don't understand, type C-g (hold down the ctrl key then hit the g key). This aborts the current command.

Now go to the top of the document and type in your name, then type in the answer to each question immediately following the question.

Save the file by typing C-x C-s (hold down the ctrl key then hit the x key, then release the x key while still holding the ctrl key and hit the s key) OR choose File, then Save (current buffer) from the menu.

Exit Emacs by typing C-x C-c OR choose File, Exit Emacs.

Printing To print out your answers, use the enscript command in your xterm (shell) window as follows:

This requests that the file UnixQuestions be printed on the lab printer. The additional parameters to the print command tell the printer how you would like the document formatted. Specifically, you are asking for 2 columns, rotated to landscape orientation and add a Gaudy title.

Submit Your Answers

cp UnixQuestions ~ingram/CPSC120/lab0/YourName

cp UnixQuestions ~bouchard/CPSC120/lab0/YourName

ls ~ingram/CPSC120/lab0/Yourname

ls ~bouchard/CPSC120/lab0/Yourname

Exiting an X-terminal: To exit an xterm, type exit at the command prompt.

Exiting GNOME To exit GNOME, click on the power icon (a zero with a one through it) in the upper-right of the screen and choose Restart. In the next window, click the Restart button. The computer will then automatically reboot into Windows 7. (If you choose Log Out from the menu the computer will go back to the Linux login screen.)