A Computer Lab with No Windows, Part II
OpenOffice.org is a great package that consists of Writer, Calc, Impress and some other graphic utilities. From my experience, OpenOffice.org is 100% compatible with Microsoft Office. I use them both on a daily basis. I use Writer for all my word processing, and it can read MS Word files and save any document in Word format. I use Calc to store and process all my students' marks, and I use Impress for presentations. Impress is a great package that can read any PowerPoint file. In addition, all presentations made in Impress are saved in PowerPoint format by default. OpenOffice.org is so efficient, in fact, that students from other classes coming to my lab for the sole purpose of printing out their work in Microsoft formats. They say they like my lab because the server is always up and the printer works seamlessly all the time.
Students can bring in their work either on a disk--I enable local disk access--or downloaded from an external FTP server. I control my printer with lpc, thus the simple command lpc enable all turns the print spool on and lpc disable all turns off the print spool. Before they can print anything, they have to obtain approval from me, thus eliminating unnecessary print jobs.
Before I put the new Xeon server on-line, I simply pulled the whole OpenOffice.org package off the menu option, as it requires a lot of server resources. In fact, with my old terminal server, I have to set Icewin (a lightweight X manager) as my default desktop manager and put GNOME and KDE off-line.
With my new dual Xeon server, I have 1024x768, 16-bit color resolution, KDE, GNOME and OpenOffice.org on-line for every student in my lab.
The new dual Xeon server, with 2 2.4GHz CPUs, 4GB of RAM and an Ultra320 SCSI hard drive (no RAID), supports 28 diskless workstations smoothly. After entering the user's password, it takes about seven seconds to load up a KDE desktop. It takes about five seconds to load Writer, Calc or Impress. In order to have the same performance in a Microsoft environment, each workstation would need, at minimum, a 2.0GHz CPU, 512 MB of RAM and a SATA drive.
With only 512MB of RAM on my Squid/router server, most students agree that we have the best Web access in the whole school building. In fact, many students from other classes come to my lab for Web surfing during their lunch breaks.
I believe the Linux terminal server network is, in fact, the best environment for teaching computer programming, operating systems and networking. The shell offers an introduction to operating systems and basic programming skills (simple shell scripts). With a rich library of TCP/IP dæmons and clients, Linux also is the perfect platform for teaching networking. Even though it might be a bit more difficult to start, using text-based command-line input instead of drag-and-drop, most students agree they understand concepts of networking and TCP/IP much more thoroughly when Linux is taught. Many graduates who now are studying at the university/college level said they are considerably farther ahead than their classmates who have exposure only to Windows.
Before I switched my lab to the present Linux terminal server setup, it was sometimes hard to run Java applets for testing on Microsoft Windows. Most Windows browsers (IE or Netscape) do not have Java support by default, and it sometimes took many steps simply to re-run an applet. When doing Java with Windows, we had to go to the command prompt to execute the Appletviewer. On the other hand, Appletviewer works quite smoothly on X.
Linux terminal server environments follow a typical central computer processing model. It is almost exactly the same as working on a mainframe or minicomputer, except it provides an elegant X window manager, such as KDE. As such, many shell commands are available that an administrator/teacher can use to monitor and control the server. Here are some that I use on a daily basis.
1. Log in as root to the terminal server and use as xterm session to run the following commands:
w: find out who is doing what on the server, a simple but powerful command
finger: find out details about all the users on-line (their real names, for example)
df -h: amount of free disk space in human readable format
top: resource monitoring (RAM, swap, processor resources, processes)
lpc enable all: enables printer spooling
lpc disable all: disables printer spooling
lpq: checks the printer que
lprm: removes a print job from the printer que
stop: a script I wrote that allows root to kick any user off the server, shown below
#!/bin/sh # stop # script to logoff a student # if [ $1 != "root" ] then for i in $(pgrep -u $1) do kill -9 $i done else clear echo "Can't kill the root!!" fi
2. Log in as root to the router/Squid server and use view /var/log/httpd/access_log to review Internet access records from any system. To block access to an Internet site, I wrote the following script:
#!/bin/sh # block # written by C T Leung # November 15, 2002 # add this line to block all ip packets to/from chaos /sbin/route add -host chaos.wsd1.org reject
chaos.wsd1.org was set up so network technicians from our school division could download drivers, and its usage is limited to authorized people. In the above example, the uncontrolled Web proxy server chaos.wsd1.org is blocked with a single line of code. Without Linux or without direct programming access to the school router, network technicians have to set up blocks on each student's Windows computer, which is both time consuming and error-prone.