I have been using LTSP for a while to turn old PCs into X terminals. LTSP works well for a desktop PC that can use PXE or Etherboot. LTSP does not work as cleanly on old laptops with PCMCIA network cards. In these cases, the kernel has to be installed on the laptop hard disk, but the rest of the LTSP installation runs from the server. When upgrading LTSP, the kernel on the hard disk gets out of sync with the modules on the server, and the laptops stop working as terminals.

I’ve been looking for a simpler setup for a laptop X terminal, and I’ve found ThinStation. It is a customizable Linux distribution designed for building terminals. The entire terminal image can run locally, from the hard drive or a bootable CD. The typical image takes up 5 to 10 megabytes. In this way, the server software can change versions, but the terminal is still standalone for its software versions. Thinstation does support centralized configuration files, giving you centralized control of options without linked dependencies.

Thinstation comes with software for several terminal types, including X Windows, VNC, NX, and Windows RDP.

Sound on Thinkpad T41 with Fedora Core 4

I have Linux running on an IBM ThinkPad T41 laptop. I recently upgrade from Fedora Core 1 to Fedora Core 4. Several things broke from upgrading, including sound.

A number of people have had sound problems with FC4, requiring various solutions such as disabling the soft modem.

Some people had problems where their mixer settings were muted. Mine was similar. I am familiar with the Linux OSS sound system used in kernel 2.4, but I am unfamiliar with the ALSA sound system used in kernel 2.6.

I verified that my sound hardware was detected, using various utilities like system-config-soundcard, lspci, and lsmod. Under KDE, I used kmix to set the volume and unmute the sound channels. The artscontrol display showed me that all of the software believed it was pumping sound to the soundcard when playing a song in xmms. It was starting to look to me like my hardware and sound module setting were good, but I was somehow muted.

I discovered that in addition to volume levels and mute settings for input and output in the sound mixer, ALSA also has some additional on/off switch settings. I do not recall seeing these with the earlier OSS sound drivers. In the case of this T41 laptop, I found a mixer switch called “Headphone Jack Sense”. Turning this off gave me working sound immediately.

KVM Custom Power Supply

Custom KVM power supply I acquired an older Connect-Tek KVM (PC keyboard/video/mouse) switch. I got it for free because it was missing the power supply. I decided to make one. KVM front KVM back

I sent an email to the company and received a very helpful reply about the specifications of the power supply.

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Following are the specification of the power supply it used: Output: 12V AC center tap, 1.2 amp Pinout of 5 pin din: the 2 extreme outside pins are VAC Center pin is center tap Shell is grounded. It may be available from: Condor Electronics, 408-745-7141 Part# WP573512CG-5DIN: verify the specifications before you order.

I decided for fun to build my own power supply to these specifications. This is not a project that one would undertake to save time or money. Rather, this is a project to do simply for the enjoyment of creating something and seeing it work and be useful.

Safety: Working with electricity can be dangerous. The 120V electrical input is hazardous, and can possibly injure or kill you. If you don’t know what you are doing, ask an expert and learn about it. Observe and follow all proper safety precautions.

Looking at the specs, this is a very simple power supply. The input and output are both alternating current, so it only requires a simple transformer, and no electronics to convert AC to DC. The only term I was not familiar with was “center tap”. This means that there are 3 output wires: two “outer” and one “center”. Between the two outer wires it is 12 volts, but from either outer wire to the center it is 6 volts. (This works the same as U.S. 240V split-phase household electrical wiring.)

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The current rating of 1.2 amps is somewhat large compared to your average little power adapter. It is important that your wire is large enough to carry the current without overheating. Wire size is a function of amperage, regardless of voltage. I consulted a wire gauge chart to find the minimum wire size required to carry 1.2 amps. Looks like I need at least 21 gauge wire (smaller gauge number is larger wire). I had some 24 gauge wire and 18 gauge, so I used the 18.

The power connector on the box is called a 5-pin DIN connector. It is the same connector used on the older, larger AT-style PC keyboard connector. Since I had a dead keyboard in my junk pile, I decided to reuse the connector from it for this. When I compared the wires in the keyboard cable with other wire I had, I decided they were too small for the amperage required. I cut off the cover from the connector with a hack saw, and soldered on the 18 gauge wire. Then I covered it with silicone sealer, which you can get from your local hardware or home-improvement store. I wrapped it around with masking tape while the silicone dried overnight. Masking tape DIN connector DIN connector DIN connector

Then when it dried, I removed the masking tape, leaving an insulated but flexible connection.

I ordered a 12V center-tap transformer from All-Electronics, part number TX-122. Then I tested it to see if it worked. Voltage check, KVM off Voltage check, KVM on

Fortunately, it worked! You can see in the pictures that the power supply said it produced 14 volts with no load, when the KVM was off. It then dropped to 13 volts when the KVM was powered on. This is normal.

It is important to encase the transformer in a box for safety reasons. You can’t leave the electrical wires out and exposed because the 120V input is hazardous, and if any metal shorted out the pins you could damage your equipment. A small plastic box is ideal. I found a small plastic truck of about the right size and shape, so I decided it was the perfect case for my transformer. TruckTruck gutsTruck base

It contained a small friction motor, the kind where you push it forward along a surface to wind up the flywheel and then let go. I removed the friction motor and the other axle. I then used screws to hold the wheels to the base, leaving room for the transformer in the middle. I drilled a 1/4-inch hole in each end for the wires, and soldered them to the transformer. Note the ground wires: since the power supply specification said the DIN shield is grounded, it will be connected with the transformer mount to the 120V ground. WiringWiring in base

Once it was done, I put the KVM and power supply on the shelf with my computer equipment. The project was a success. Connected to KVMInstalled

Submitted by amillar on Mon, 2005-08-29 06:49

Limiting web browsing on LTSP terminals

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With LTSP, all applications run on the server. This is great for the low maintenance involved: install an application program once, and it is available immediately on all terminals.

However, some times you may want to discriminate between different terminals. For example, you may want to restrict web browsing at one terminal or another.

Because the browsers run on the server, all outgoing HTTP connections come from the same machine. This means you cannot just restrict by IP address. You need a finer grain of control, by X display.

There is no easy perfect solution for this problem. The best solution would be to have two different terminal servers, and have the two classes of terminals connect to the appropriate server.

I’ll describe my hack attempt to solve this problem. My approach was to set browser proxy settings based on the X display.

First, you must decide how you want to limit the browser. In my case, I created two browser proxy configure scripts, which are usable by Netscape, Mozilla, Opera, and Internet Explorer browsers.

Script for allowing internet access: “proxy.pac”

function FindProxyForURL(url, host) { if (isPlainHostName(host)

Mac on Linux

Mac on Linux is a software package for Linux running on a PowerPC processor. It will allow you to run MacOS in a virtual machine.

It is similar in concept to VMWare GSX, where the disk images are stored in the host’s file system but the guest VM screen is not tied to the host’s screen.


I’m running it on an old Power Computing PowerCurve Mac clone. It has been upgraded to a 225MHz PPC 604 CPU and 128MB ram.


Submitted by amillar on Sun, 2004-02-01 21:01