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How can I improve the Java applet screen refresh speed with Ubuntu LTSP?

A certain version of the X11 library does not work well with Java's screen updating. A customer of ours and user of LTSP, Juha Erkkilä, figured out a solution to this problem: http://www.mail-archive.com/ltsp-discuss@lists.sourceforge.net/msg35132.html

The sluggishness of some Java applications can be solved in Ubuntu Hardy by replacing the /usr/lib32/libX11.so.6.2.0 file in Hardy with the version in Gutsy (presuming Firefox and Java are 32-bit versions, so they use 32-bit libraries). The main difference between these versions appears to be that the Hardy version links to /usr/lib/libxcb-xlib.so.0 and /usr/lib/libxcb.so.1, and the older version does not. A similar change may work as well with other LTSP distributions that are affected by this. I do not know what it is in the actual X11-client implementation that makes this difference, but it appears to make a dramatic difference with many Java applications.

Another way for improving the screen drawing is to apply these few changes:
  1. Edit /opt/ltsp/i386/etc/lts.conf and add there these 3 rows:
    [default]
    LDM_DIRECT = true
    X_COLOR_DEPTH = 16
  2. Next, run this command to update the client software (affects next time when the terminal's restarted):
    sudo ltsp-update-image
This will make things much faster, it also allows the client to not encrypt all the data through SSH.


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Last Updated
28th of September, 2012

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