Server load spike debugging

[Daniel Shahaf]

David Suna wrote on Wed, 25 Apr 2018 22:12 +0300:
>  I am working on a VPS. Earlier today there was a load spike that made
>  the server unresponsive for a period of time (around 10-15 minutes).
>  Both ssh and web access were not responsive. After a while the problem
>  just stopped and the server started responding again.
> 
>  How can I go about diagnosing what caused the problem?

It might help to keep an ssh session open throughout the day with a root
shell (real '#' prompt, not just sudoable unprivileged shell) running in
it; such a shell might be usable even when the CPU contention is so high
that new ssh logins aren't possible.