terminals randomly disconnecting

[Krsnendu dasa]

On 12/01/2008, Krsnendu dasa <krsnendu108 at gmail.com> wrote:
>
> I have noticed a few other problems and narrowed down the problem (I
> think) to either os problem or motherboard problem. (Don't think it is the
> switch or the network card.) Read below for more details. Thanks for all
> tips.
>
> On 07/01/2008, Gavin McCullagh <gmccullagh at gmail.com> wrote:
> >
> > Hi,
> >
> > On Mon, 07 Jan 2008, Krsnendu dasa wrote:
> >
> > > I am experiencing an unusual problem. Occasionally (every 15 mins or
> > so) all
> > > the terminals just disconnect. The terminals need restarting before
> > they
> > > work again.
> >
> > What you say all, you mean every thin client connected to the server?
>
>
> Yes. Also windows computers that were connecting to the internet and using
> dns through the edubuntu server also had disconnection problems. I changed
> dhcpd.conf to get dns from another server and it seemed to fix the windows
> laptop to internet problem.
> I am having intermittent problems with samba also. One minute I can
> connect to the shares on edubuntu then the next minute I can't then I can
> again. It seems to take a long time for the server to register when new
> windows computers in the workgroup have connnected. At one point I noticed
> that nmbd wasn't running so I manually restarted it. This is after I had
> already restarted samba using init.d and webmin.
>
> Every 15 minutes is pretty nasty.  I guess at least it's easy enough to
> > repeat if you're testing.
>
>
> May not be exactly every 15 minutes, maybe closer to 30mins.
>
> You say the clients need restarting and I gather the server doesn't.  Can
> > you ping a thin client after this happens (ie without rebooting it)?  If
> > you press <ctrl><alt><backspace> is that enough to restart the thin
> > client?
>
>
> I haven't tried this as I haven't been at school much. I will try it next
> time I  am at school when it freezes.
>
> > In what I think may be a related issue, some times when someone is
> > logged in
> > > their terminal freezes and the panel at the bottom of the screen which
> > shows
> > > which windows are open just has three tabs that all say untitled
> > window.
> >
> > Have you had opportunity to watch top for a few minutes and see does
> > some
> > process go wild around this point?
>
> I haven't noticed anything. I will look again and see if anything stands
> out.
>
> > Background: I am using 32 Edubuntu 7.04 on Intel Quad Core. 4 Gb RAM. I
> > am
> > > using directx ldm and smbldap.
> >
> > Would it be possible for you to try not using direct-x and go back to
> > the
> > default ssh method?
>
>
> I can also try this, but my instinct (and the dns /samba problems) seem to
> point to bigger connection problems than ldm.
> I also get disconnected when I log in from home using nx.
>
> > I am using a 100/1000 unmanaged switch which feeds 10/100 switches in
> > each
> > > class.
> > >
> > > Things I have already tried.
> > > At first I thought it could be the 1000 switch, so I swapped it for
> > another
> > > one, but the problem remains.
> >
> > Was it another similar switch?  Could it be a problem between the
> > switches?
>
>
> The second time I used a different brand of switch and a 10/100 switch, so
> I don't think the switch is to blame.
>
> > Possible solutions:
> > > Could upgrading to Gutsy help?
> >
> > It's hard to say without knowing what the cause of the problem is.
>
>
> If may be my old windows conditioning, but I feel like a reinstall might
> help... or not.
>
> > Could it be the network card in the server?
> >
> > Sounds plausible.
>
>
> I tried another network card and the same problems are there.
>
>
> > Can someone help me debug this? Are there any log files I can check to
> > trace
> > > the origin of this problem?
> >
> > Yes:
> >         /var/log/syslog
> >         /var/log/messages
> >         /var/log/kern.log
> >         /var/log/daemon.log
>
>
> I had a look there and couldn't find anything that stood out for me. A few
> times I saw something that said "disconnected" or something like that.
> Perhaps I will copy and paste a section around the time when a disconnect
> happens and post it for any experts to analyse.
>
> > Thanks for any help. This is really frustrating, because I had a very
> > stable
> > > system with K12LTSP 6, and now with Edubutnu 7.04 I have having quite
> > a few
> > > problems.
> >
> > How long have you had this problem?  You've been using 7.04 for a while,
> > right?  Has it always happened?  Has anything changed to prompt this?
>
>
> We installed some time in October. This problem has been only since
> December. I can't think of anything that changed at that time. The last
> thing I remember that changed is... A course management software web-based
> application was installed and there were some changes to dns.
>

Back to the drawing board... I have installed Hardy and the problem
persists. I will have to investigate the network and system more thoroughly
and document it robustly.

Summary:
Initial Problem: Feisty install of Edubuntu - One Network interface: Server
randomly disconnects from the network about every 20-30 mins. Terminals left
with 3 unusual untitled windows tabs at the bottom of the screen.
ALT-Ctrl-backspace usually allows users to log in again.

Tried using another network card, switch etc. Ran Wireshark to look for
network problems.

Tried changing the system to a new box. Problem persists.

SSH mostly seems affected. Even when I can ping the server I can't ssh in. A
few minutes later I can ssh in. At the same time I can ssh in from one
machine, but not from another machine.

Sometimes the server can ping a machine, but that machine cannot ping the
server.

I installed Hardy with 1 network card: problem persists.
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