comparison

[Gavin McCullagh]

Hi,

I don't know much about K12LTSP.  What version of LTSP does it use?
Edubuntu uses LTSP v5 which may be the difference in some of these.

The older LTSP (as I understand it) uses XDMCP straight across the network,
whereas v5 uses ldm running locally to start an ssh tunnel to the server.
This tunnel might have an effect on application responsiveness.

Is local device support (usb keys, digital cameras) work on K12LTSP thin
clients?

On Thu, 31 May 2007, Ray Garza wrote:

> Booting to the logon screen is about the same. 
> -- Edubuntu: 1 minute and 33 seconds 
> -- K12LTSP: 1 minute and 42 seconds

That's interesting.  Edubuntu is sometimes very slow to boot on thin
clients but seems not to be here..

> Going from the Logon screen to the Desktop, K12 is a lot faster.
> -- Edubuntu: 17s
> -- K12LTSP: 6s

Interesting.  If you turn off LOCALDEV and SOUND on a thin client (just for
the sake of interest), does this change much?

> Playing Tux Type w/sound is a lot faster on the K12 system
> -- Edubuntu system: Tux Type was very slow even at its Highest level 
> (Commander w/short words)
> -- K12LTSP system: Tux Type played just fine

Possibly due to the tunnel.

> Another thing that I noticed is that I can't (or couldn't figure out) change 
> the logon screen on the client PC. On the K12 system I would goto 
> System-->Administrator-->Logon Window and make the changes there but it 
> doesn't work on Edbuntu.

This is the difference between ldm and xdmcp.  You need to modify some
settings in /opt/ltsp/i386/usr/share/ldm/themes/ to change the thin client
login screen in edubuntu.

> The Dell Optiplex 620 works fine under Edbuntu. Sound works on the 
> Applications that have sound and Tux Type or Tux Math work fine. Maybe I'll 
> use Edbuntu for the lab with the new Dell's and K12 with the older stuff. I 
> would like to run both with one system.

The ssh encryption adds a CPU load to the thin client (and the server).
This may be part of the problem here if your more powerful thin clients
aren't bothered.

> Any comments? Anthing I can do to get Tux Type and Math to run at it's normal 
> level? I imagine that if I switch to NIC that can boot off the Network some 
> of the sluggishness will go away.

Various people have suggested patches to openssh to add a null cipher, ie
to not encrypt data in transit.  The guys at PSC provide a patch:

http://www.psc.edu/networking/projects/hpn-ssh/

however the openbsd folk don't seem to be keen on it.  If you have the
knowledge to do it, you could try patching openssh and installing it into
both the server and thin client chroot (prob /opt/ltsp/i386), then modify
ldm to change the cipher it uses and see does it make a big difference.

You could also (if you fancy rolling up your sleeves) try setting up your
edubuntu thin clients to use XDMCP instead of LDM and see does it make any
difference.  I don't suggest using it like this in general, it would just
be interesting to see do your problems go away.  This may break some other
stuff like sound though.

Most of these are changes that would be interesting as experiments.  I'm
not sure if you'd want to actually deviate too much from the standard setup
in production though.

Gavin