LTSP network freezing in Dapper

[Hendrik Boshoff]

Hi
 
My last post was around six months ago, and now I have some problems
with Dapper on the 40 client setup at my children's primary school.
 
Instead of upgrading Edubuntu Breezy, I created new partitions for
Dapper and home, and did a fresh install at the end of June. I then
copied some configuration files, including passwd, group & shadow, and
ltsp & dhcpd.conf, and mounted home separately in fstab. Right out of
the box, I had some booting problems, even had a server crash once,
which went away with updates.
 
After reading a bit in O'Reilly's book Running Linux, I installed
postfix to enable local mail delivery between the children's accounts.
This is actually a nice sandbox to learn email without Internet
connection, and it avoids undesirable content entering the server via
that route.
 
At some point I tried Sabayon, which did not work for me, and I removed
it again. Some extra applications were also installed (including
KAsteroids).
 
Recently, the network started freezing randomly. The timing is
unpredictable, but every client ceases getting response from the server
at exactly the same point. Waiting for about three to five minutes
usually allows the system to resolve the problem automatically. Neither
the CPU nor the network load is heavy at the time, and the response on
the server terminal is perfect. I noticed two other things: The lights
on the network switch flash in unison at a rate of about 2 Hz under this
condition, and a perl script with a name similar to network-conf floats
to the top of the process list in terms of CPU time used. Cycling the
power on the network switch seems to get the server to attend to the
problem sooner, but I may be imagining this.
 
There are sometimes problems as well with timeout of the NFS mount of
/root during LTSP client booting (the second ok expected on the brown
boot screen).
 
I proposed to the teacher that we could go back to Breezy, but he
insisted that Dapper works better on the whole. When the network freeze
happens during class time, he reboots the server, which temporarily
helps. This problem did not occur under Breezy, and everything still
works fine most of the time.
 
It is true that my knowledge is lacking, and I know that I am dangerous
trying to perform tasks I don't quite understand. It is also possible
that during my experiments, I changed some setting which I never
reversed.
 
So what are my options? How do I troubleshoot LTSP networking? Do I
reinstall on a third partition and be more conservative about changes to
the default this time? I would not like to roll back postfix, the kids
enjoy their email too much. I suppose I should get on IRC over the
weekend for some assisted troubleshooting in real time. Any other
suggestions?
 
Thanks
 
Hendrik Boshoff
hfvb at ing.rau.ac.za
 
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