Troubleshooting a lockup

[Luke Dean]

I run a headless machine that has sporadic lockup problems, and I need 
some advice on what I can do to gather enough information to give me some 
idea of what's causing it.

The machine acts as a router, DNS, web server, mail server, nfs server, 
firewall, and lots of other services.  These problems started occurring 
after I upgraded from FreeBSD 5.4 to 6.0 and installed a secondary hard 
drive controller.  Before that it ran perfectly for months at a time. 
That's a lot of variables to rule out.

When the lockups occur, both network interfaces just plain die.  Also, if 
I bring over a monitor and plug it in, I can't get a video signal, even 
if I tap the keyboard to wake it up.  The lights on the keyboard still 
work, so I don't believe the box is completely frozen.  The only option I 
have is to hit the reset button.

Inspection of /var/log/messages never gives me any clues, except for one 
time I saw one message about my rl0 interface getting a watchdog timeout, 
but that was only one time and I can't imagine why a failure on one 
network interface would cause both network interfaces to stop responding. 
Inspection of the httpd logs just gives me an idea of about what time the 
lockup occurred, since there's no activity after that point.  I don't know 
of any other log files that might be of assistance.

I thought about trying to configure a dump device, but I don't believe the 
machine is panicing, except perhaps when I hit the reset button.  I may 
try to figure out some way to disable the power management on the video, 
hook up a monitor, and leave "top" running on it to see if that gives me 
any clues.  I plan on googling for "serial terminal" this afternoon.

Any other suggestions?