mouse scratchcard effect on LTSP ThinClients

[Reinold Baur]

Binary package hint: ltsp-server-standalone

1)
Description: Ubuntu 8.04.3 LTS
Release: 8.04

2)
ltsp-server-standalone:
  installed:5.0.40~bzr20080212-0ubuntu7
  possible packages:5.0.40~bzr20080212-0ubuntu7
  version-table:
 *** 5.0.40~bzr20080212-0ubuntu7 0
        500 http://de.archive.ubuntu.com hardy-updates/main Packages
        100 /var/lib/dpkg/status
     5.0.40~bzr20080212-0ubuntu6 0
        500 http://de.archive.ubuntu.com hardy/main Packages

3+4):

Description of the problem:

Sometimes parts of the screen become grey. This problem is not reproducible (it happens perhaps every 1 hour). I can not tell you when it exactly happens.
It feels like a scratchcard which the user has to scratch with his mousepointer. I searched the web to find a solution for that problem, and I found a user who had the same behavior with VNC.
It seems that the protocol the LTSP system is using is optimized to transfer only GUI-Elements wich has changed. But this optimization seems to work not fine.

Possible solution for hotfix:

Perhaps you can write a hack that refreshs all parts of the screen e.g. every 1 second. I have tried to look into the source code to write a hotfix, but if you do not know where to look, it is a long search...

Impact of this bug to the work of my users:

low - working is still possible.
I told the users to press CTRL+ALT+F1 and after a second press CTRL+ALT+F7 again. The X-Server reloads the screen and the user can work further more.

Thanks and regards,

Reinold

ProblemType: Bug
Architecture: amd64
Date: Mon Sep 7 12:23:44 2009
DistroRelease: Ubuntu 8.04
ExecutablePath: /usr/bin/yelp
Package: yelp 2.22.1-0ubuntu2.8.04.3
PackageArchitecture: amd64
ProcEnviron:
 LANGUAGE=de_DE:de:en_GB:en
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: yelp
Uname: Linux 2.6.24-24-server x86_64

[Stéphane Graber (stgraber)]

There is no such thing as a LTSP protocol, LTSP is based on regular X11 which is the same protocol that all your local softwares are using on your computer.

The problem you are describing can't happen with X11 as it's never sending actual part of the screen but rather X11 events and bitmaps just as it happens on a local computer.

If you get screen corruption, it's more likely to be a video driver issue, for that knowing what the video card is in your thin client would help.

It'd also be interesting to test with 9.04 or even 9.10 and see if the issue is fixed there (with new ltsp, new kernel and new video drivers).

[Reinold Baur (mail-reinold-baur)]

Thank you for your help.

The video card which is in my thin client:
(lspci | grep vga)
01:00.0 VGA compatible controller: VIA Technologies, Inc. VT8623 [Apollo CLE266] integrated CastleRock graphics (rev 03)

I have done several tests with Ubuntu 9.10. It seems, that the error does not exist any more in this version. And with other thin clients (VMWare or Intel Atom) the problem does not exist in 8.04.

[Scott Balneaves (sbalneav)]

ok, video driver issue not related to LTSP, but rather Xorg.
Closing.