Hanging server

[Paul Lussier]

Hi all,

We've got system which is demonstrating some bizarre behavior and I
was wondering if anyone here has seen something like this or had any
ideas.

I have a box running a modified Debian/woody system and 2.4.31.  It is
intermittently hanging such that:

* All logging to /var/log ceases.
* Machine is still pingable.
* Machine can be telneted to on time port, but no time is echoed.
* After attaching a console+keyboard, console would not unblank.
* Nothing responded when attaching a serial console.
* Machine does not respond to Ctrl-Alt-Del
* No DMI messages are logged.
* Hang is persistent until physical reboot.

This has happened 4 times, on 2 separate machines (under roughly
similar conditions).  Nothing unusual is logged in
/var/log/{deamon.log,kern.log,messages,syslog} prior the hang.

The machine is under relatively high load and has a custom userspace
nfs server running on it (which is potentially to blame, but we've
been unable to determine how).  The custom userspace nfs server and
tomcat4 are the primary applications running.

Any suggestions as to how I might debug this or possible causes would
be greatly appreciated.
-- 
Thanks,
Paul