I have an Ubuntu server that has recently been intermittently slow to respond - 30s+ to connect to ssh or web servers, and New Relic shows regular interruptions in the data (but no actual activity).
Every time I look at it the load average is under 0.1. I can't see signs of excessive activity in any of the services running.
If there is no sign of activity on the server how can I find what is making it slow to respond?