15-122 Principles of Imperative Computation
Recitation 1 - Wed Jan 12

Navigating your account in Linux
Editing your program
Compiling your program
Running your program
Accessing your Andrew files using ssh

Navigating your account in Linux

Open up a Terminal window to access the Linux command prompt. (Unlike typical graphical interfaces for operating systems, here you are entering commands directly to the OS and can change hundreds of options to give finer control of what you're doing.) On the Linux machines in the computer labs in Gates (rooms 5205, 5201, and 3000), you can access a Terminal window using the Applications --> Accessories menus.

In the Gates computer labs, your terminal window will give you a prompt and you will be in your home directory in your Andrew account. Type ls (to list files) to see what files and directories are there. Back in the day, we used to call folders "directories". To move to another directory, use the cd command (for "change directory"):

cd private

ACADEMIC INTEGRITY NOTE: You should store your program files inside the private directory (or a subdirectory inside this directory) since this directory is automatically set to prevent viewing by other users. Remember that you should protect your code from being viewed by other students as part of the academic integrity policy for this course.

Since you will write a number of programs for this course, it pays to make a subdirectory inside the private directory. Once you cd into the private directory, make a new directory named 15122:

mkdir 15122

Now go into this directory using cd again:

cd 15122

To go back up one directory if you need to, use this command:

cd ..

You can go up two directories and down another directory (e.g. public) like this:

cd ../../public

If you ever get lost while you change from one directory to another, you can use pwd to find your present working directory. Or if you want to go back to your home directory, simple type:


You can also access any directory from your home directory using the shell variable $HOME or the "tilde" character ~. For example, you can get to your 15122 directory from any directory on Andrew by typing this:

cd $HOME/private/15122

or this:

cd ~/private/15122

LOGGING OUT: Remember that you must log out from the computer in the Gates lab. Closing the terminal window is not enough! To log out, go to the System menu and choose Log Out. You don't want others accessing your account if you leave yourself logged in.

COURTESY NOTE: In the Gates labs, if you don't use your lab computer for a set period of time, the screen saver will launch and you can't access the terminal unless you type your password in. Some students have left the computer this way so they can "reserve" the machine for themselves later. If we find a machine in screen saver mode and no user at that terminal, we will automatically log you out so you may lose work if you're not careful. Please be considerate of others and don't lock the terminal.


Computing Services - Unix Help Page

Setting up Your Account for C0 mode and running the compiler and Editing your program

You can use any editor you wish to write and edit your programs but we highly recommend you try out emacs since this editor can do much more than just help you edit your code (as you will see).

To set up emacs for your Andrew account, you will need to create a configuration file named .emacs in your home directory. Run the following configure command located in the course directory and redirect the output into the .emacs file:

/afs/andrew/course/15/122/c0-mode/configure >> ~/.emacs

When you want to edit a program now, you can enter emacs specifying the file name you want to edit. You should be in the directory where the file is or should be (to keep things simple for now). For example, to open the file test.c0 in emacs, you'd go to the directory where this file should be stored and enter:

emacs test.c0

If the file exists, it will be loaded into the emacs editor. If the file does not exist, you will get a blank editor to start typing in the code. The configuration file .emacs you edited earlier will add color coding to your c0 programs. Keywords will show up in one color, variables in another, etc. This will make it easier to edit your program code.


LinuxHelp.next Emacs Help

Before you compile programs, you should update your path in your Andrew account so the system can find the C0 compiler without you having to explicitly give the full path to the compiler's location.

To update your path, use emacs to edit the file .cshrc found in your home directory when you log in:

emacs .cshrc

Add the following line at the end of your .cshrc file exactly as shown:

setenv PATH ${PATH}:/afs/andrew/course/15/122/bin

Save the file and exit emacs. For this time only, you can have the system run this resource file immediately by entering the following at the Linux prompt in your terminal window:

source .cshrc

(When you log in next time, this file is "sourced" automatically.) If you use a different shell than csh, you will need to adjust your path accordingly. See your TA or CA if you need more help.

Accessing your Andrew files using ssh

You can always access your Andrew files on the Andrew Linux server in the Gates labs (rooms 5205, 5201, and 3000) when the labs have no classes scheduled. In addition, you can access your files via ssh in several ways. ssh (secure shell) a protocol for securely logging into remote servers like the Andrew system.

Windows machines: Download a free ssh client like PuTTY. When you log in, specify the server linux.andrew.cmu.edu.

In the Windows clusters on campus, you should run X-Win32 first and then use an SSH client like SSH Tectia-Terminal to log in to linux.andrew.cmu.edu. By having the X-Win32 program running, all "windows" that you open up when logged into andrew (e.g. when you run emacs) will appear on your local Windows console.

Mac and Linux machines: Open up a terminal window and run this command:

ssh -X -l yourusername linux.andrew.cmu.edu

and enter your password when prompted to log in. (Your machine might ask if you want to add the server to a list of known hosts; if so, answer yes.)

written by Tom Cortina, 1/12/11