Quick & Dirty Guide to Getting Started in CSE 303

["Accessing Linux" instructions revised 1/05/2008. HP]

This document is a set of basic instructions for getting a Linux prompt and doing work in CSE 303. The home systems for the course are the instructional Linux workstations in the labs and the server attu.cs.washington.edu. All of these machines share a common file system. It's easiest to work in the basement labs where we have checked that the right software is installed and the directions we supply are correct. But there are many ways to work from other machines, which are described below. In any case, you should verify that your projects work properly on the lab machines or attu, since these are the reference systems for the course and we will check your work there.

Accessing Linux

Linux Machines in the CSE Labs

The easiest way to go is just to use one of the Linux workstations. When you log in you will have a Unix shell and your current directory will be your home directory in the department's Unix filesystem tree.

Connecting to attu From Lab Windows Machines

You can use Reflection X on the lab Windows machines to get a graphical interface for your Linux session on attu. Simply double-click the "SSH-X attu" icon on the desktop. Type in your CSE account password and you're all set.

Accessing your Linux home directories from Windows

If you're in the basement labs, your O: drive should already be mapped to your Unix home directory. Look under for the O: drive under "My Computer" in the Start Menu. To access your files, go to O:\unix\homes\iws\userid, replacing userid with your own CSE account username. All the files you saved while working on attu should be there.

If you're in the labs and your O: drive isn't mapped, open up a Windows Explorer window (by clicking the "My Computer" from the Start Menu) and in the Tools menu item, select "Map Network Drive" and enter O: for drive and \\ntdfs\cs for folder. Click Finish. If you're at a computer that does not use CSE's name servers, for example in Mary Gates Hall or at home, you will need to use the fully qualified name, \\ntdfs.cs.washington.edu\cs.

For more info on this, see the CSE support page that discusses Microsoft DFS, which is what we just used.

Connecting to attu Remotely

Connecting from Windows

Install Reflection X on your Windows computer, using the CSE department instructions. What a Reflection X session does is connect you to a CSE UNIX server. Everything you type or click is sent to the server, which sends back to your computer what to display. So you're using the department's software installation. If you don't want a full multi-window login session, you can use PuTTY by itself to open a simple single-window remote session and use it for your work.

If you've installed the cygwin package on Windows to get a full Unix-like environment (see below), you can use its ssh and scp commands to get a basic terminal connection that works the same as described below for OS X or Linux.

Connecting from OS X

If you have a Mac there are two ways to connect to attu: either through a basic terminal window or with a full X-window interface.

The basic terminal window is simplest: start the mac Teminal application and enter ssh attu.cs.washington.edu. This connects the terminal window to attu and everything you do will run in that window, including things like emacs. To get your work done, you may well have to bounce back and forth in this window between different programs like emacs and the shell.

You can also get a full X-windows interface, the same as that provided by the Reflection X package on Windows. For this, you first need to be sure that you've installed the X11 program, which is Apple's version of X windows. This is an optional installation package that you can find on the system disks that came with your Mac or with your OS X upgrade. Once it is installed, run the X11 application, which is in Applications>Utilities. X11 should pop up an xterm window (something different than the regular Mac terminal program). Enter ssh -Y attu.cs.washington.edu to get a full X-windows session on attu. Depending on your network connection, this might, or might not, be acceptably quick and responsive.

Regardless of whether you are using the OS X Terminal application or X11's xterm, you can use the scp command to copy files back and forth between your local Mac disk and the attu filesystem.

Connecting from Linux

If your remote machine is running a reasonably current Linux distribution you can use ssh in a terminal window to connect as described for OS X above. Simple ssh will give you a single terminal window interface; ssh -Y will give you a full X-windows connection. You can also use scp to copy files between your local machine and attu. You should not need to do anything extra to install X windows on most Linux distributions.

Working Directly on Your Machine

While you can do all your work connected to attu, sometimes this is not possible, or is not convenient because of slow network connections or other issues. There are versions of bash, emacs, gcc, etc. for other systems that you can use. However, you should double check your work on attu before you submit it, since there are sometimes subtle differences between versions of the GNU tool chain installed on different systems.

Linux: If you have a linux system, you're all set. Open a terminal window and work locally.
OS X: Apple's OS X is a version of Unix, and has most of the Unix tools built in if you have Apple's developer tools installed. You can get the latest version free from http://developer.apple.com/ (free signup required - click on the ADC Member site link). Warning: the developer tools disk image is huge; you'll want to download it somewhere that has a fast network connection. One thing that Apple does not have is a fancy version of emacs that runs in a separate window. There are several emacs ports for OS X available on the web; the Carbon Emacs port available on Apple's download site (http://www.apple.com/downloads/macosx/unix_open_source/) is one good choice.
Windows: the Cygwin package (http://www.cygwin.com/) provides a Linux-like environment. After installing, you'll have a bash shell and all the standard Linux utilities, but these are really Windows programs that have been written to act like the corresponding programs on Linux. For emacs, go here (direct download link: ftp://ftp.gnu.org/gnu/emacs/)

Basic Unix commands

To move around through the directory structure in your xterm window, you'll need to know a few basic Unix commands.

attu4% mkdir mydir
attu4% ls
mail  mydir
attu4% cd mydir
attu4% pwd
/homes/iws/sbfan/mydir
attu4% exit

In the above (the things within the quotation marks are commands to type, don't type the quotation marks themselves):

To make a directory, and name it, say "mydir", you would type "mkdir mydir".
"ls" lists what you have in your current directory.
"cd" will change directories. To change to a directory "mydir", for example, type "cd mydir". To move back out of a directory, type "cd ..", and to get back to your home directory, "cd ~".
To check where you are, type "pwd".
"exit" exits.
To get help on some command, say you want to know how to use "ls", type "man ls" and you will get the manual pages for that command. (Alternatively, you can use "info" in the same way.)

These are just the very minimum basics, or course.

Changing your shell

The shell is the program where you type in commands. There are different shell programs, which are all similar but have different rules and features. For sake of uniformity, we will use a shell called "bash" but it's likely that your account is set-up such that when you log in the shell it uses is "csh". You can change this for the time being or once and for all. We strongly recommend the latter, but we'll explain the former first to help you understand what is going on.

For the time being: Type

attu4% bash

Now you may have a different looking prompt (such as bash-3.00$). Otherwise at this point you will not notice any differences, but that's only because you don't know any differences between bash and csh. When you type

bash-3.00$ exit

you'll be back to the shell you were running when you typed bash. That is, you started running a different shell and when you exited, you just went back to the outer one.

Once and for all: You could type bash every time you create an xterm, but that's a pain and you could get confused if you forget. So you can tell the operating system once and for all that for your account, the "first shell" for every xterm should be bash. From any prompt, type:

chsh -s /bin/bash

You are running the "change shell" program and specifying that your new shell can be found at /bin/bash. It's almost that simple:

To be sure you have the right to do this, you'll be prompted for your password.
Before that, you'll be warned that typing passwords can be dangerous. Say "y".
As the message says, the change may take a few hours. In the meantime, see "For the time being" above.

As a final note, if your shell already is bash, chsh will just say "Shell not changed."

Emacs

Now that you have your xterm open, let's open Emacs.

Type "emacs &" to open emacs in a new window. Note what happens if you don't type the "&"--you can't do anything in your xterm window. The "&" runs your program, in this case, emacs, in the background.

The cursor is a rectangular block and is referred to as the point.
The modeline displays information about the buffer displayed in the current window. A buffer is a logical "thing" that you are working on. When you open a file, it will be loaded into a buffer, typically with the same name as the file.
Every buffer is edited in a mode. The most basic mode is Fundamental, which provides only the most basic Emacs editing features. There are modes for many different languages.
There are many "special" buffers that do not correspond to loaded files. The one above is called *scratch*. This buffer runs in Lisp Interaction mode.

Emacs uses many key combinations involving the Control and Meta keys. Such key combinations are denoted C-x (Control-x (lowercase)) or M-x (Meta-x). On keyboards that don't have Meta, Alt is usually an acceptable substitute. If Alt doesn't work, ESC-x is equivalent to M-x.

A sequence of key presses is written like C-a C-b M-x, which would mean do the three actions in sequence.

The most important keys in Emacs

C-x C-c: Quits Emacs.
C-g: Cancels the current action.
C-x C-f: Opens a file.
C-x C-s: Saves a file.
C-x C-w: "Save as" (save contents to file with a name you type).

Getting help in Emacs (the next most important keys)

C-h: Help. Hitting this will display a short message in the minibuffer: C-h (Type ? for further options).
C-h t: Built-in interactive tutorial. Some people don't like this tutorial, but some people find it helpful.
C-h b: Key bindings. This lists all key bindings that are valid for the current mode. Note that key bindings change from mode to mode!
C-h a: Command apropos. After hitting C-h a you can type a symbol and a window will appear that lists all symbols and functions that match that phrase.

Some other useful keys:

C-x 2: Split the window into 2 buffers, one above the other. (Use the mouse or C-x o to switch between them.
C-x 0: Undo window-splitting so there is only 1 buffer.
C-x b: Switch to another buffer by entering its name.
C-x C-b: See a list of all current buffers.

Font-coloring in Emacs

Remember the Emacs modes we were talking about earlier? The modes for shell-scripting and C programming do a pretty good job of coloring your code, but you may need to say you want that:

If you don't have a .emacs file, create one. Type "C-x C-f" and then type ".emacs". Now you're editing your .emacs file. This file must be in your home directory.
Paste the following line into your .emacs file:
```
; get pretty colors
(global-font-lock-mode)
```

That's it. To check if it works, you need to restart Emacs. Save your file (C-x C-s) and quit Emacs (C-x C-c), and open it up again. Open a file that starts with

#!/bin/bash

(or create one, close it, and reopen it). Builtins like if and set should be in different colors.

For additional information there are other resources, including the CS Lab and Support pages.

Acknowledgment: These notes have evolved over the last few years, but are largely based on notes written by Keunwoo Lee in 2001. They started as a guide to CSE 341; information on SML has been removed and information on changing your shell has been added.