crash investigation

[Nicholas Helps <n.r.helps@dundee.ac.uk>]

Hi all,

As a veritable newbie (at least in comparison) to Linux, I would like some suggestions as to how one goes about 
investigating system crashes. I have set up a couple of systems which generally run fine. However, today one of my 
debian systems stopped responding and had to be "hard" rebooted (ie press the power button - Ouch..!). This machine 
is run from the command prompt with no GUI and has a very limited set of software running on it (essentially it is 
running as a firewall and dhcp server and nothing else).

I am keen to find out why the crash might have happened. I have looked at various log files in /var/log/, but none 
seem to suggest anything obvious. Could someone with more experience suggest other information that might be help 
an investigation? The machine has not crashed before and so maybe it is just a "one off". However, without being 
able to ascertain (as far as one might be able to) what caused it, I am in the dark.

Any suggestions welcome (even if you think it is obvious or "in the manual", because I haven't read all the manuals 
yet... ;-)

Thanks,

Nick.