Wednesday, September 02, 2009

Resolution issues in LTSP

Yesterday I brought my whole class down to my newly configured LTSP lab with my dual quad core xeon, 8 gigs of RAM server powering my 22 Pentium 3, 128 MB RAM thin clients across a 10/100 switch with gigabit uplink from the server to the switch. From everything I've read this setup should work fine, especially since I've got firefox running as a local app now. Alas, it was not long before the familiar old complaints were ravaging my ears. "Mine's frozen!" "The computer's not working!" "Mine's slow!"


I did my best to alleviate the immediate issue by moving kids off of computers and that seemed to help a bit, but I still think there must be some sort of issue with my switch or something. I'm not entirely sure what the problem could be, but I knew that 128MB was pretty lean for the clients so after school I collected all the old PC133 SDRAM I had in stock and installed an extra stick in each client. This brings me to 256MB RAM in each machine which should be adequate.

I figured out how to check on the switch settings and all the ports are running at full duplex, but I've got a parent here who's pretty saavy with network issues so I might have him probe around a bit more.

One thing still left me puzzled yesterday, and that was the fact that some of the machines were not showing the screen correctly. Things were showing tracks around the screen and the resolution was different on different monitors. This despite the clients all being the same make and model. Very confusing.

It's taken me a couple of hours this afternoon, but I finally figured out the problem. I noticed that the problem was only happening on certain monitors, Dell M782 models to be exact. The Dell 781P's, which are actually a year older than the 782's, were working perfectly.

After wading through the ltsp handbook for a while and trying all kinds of settings in my lts.conf (/var/lib/tftpboot/ltsp/i386/lts.conf) I finally found the one setting that fixed all my problems:
Apparently Xrandr was trying to autoconfigure the settings on the monitor and was somehow getting them wrong. By disabling xrandr I was able to dictate the resolution I wanted and all the tracing and slow performance disappeared! Sweet. Here's my complete lts.conf if you're curious, but disabling xrandr was really the key to getting the monitor resolutions right. Cheers! -joe
X_MODE_0 = 1280x1024
SEARCH_DOMAIN = || Change this for your own network
DNS_SERVER = || Change this for your own network
RCFILE_01 = /etc/init.d/


Aric said...

What was in ur rcfile script?

Joseph Hartman said...

no idea. I didn't change that at all that I can remember. Sorry