10.3-stable random server reboots - finding the reason

[tech-lists]

Hello stable@

I have an up-to-date 10.3 server that is randomly rebooting, after being
up for days. Previously it had been up for many months. The problem is,
nothing seems to be left in the logs to indicate why it's doing this. I
have all.log and console.log enabled.

So, what I'm asking is, how can I capture its last gasp?

many thanks,
-- 
J.