Check cpu usage

Question

I noticed that while idle my CPU usage spikes to 20% every few seconds. However, activity monitor shows no process using a lot of CPU during those spikes (I have activity monitor set to show all processes). As there any way in Unix that I can track CPU usage over say 10s and find out which process causes this spike?

Answer 1

Hmm, I wonder if this is not related to a specific process, but rather something like a NIC thread or something similar which doesn't show up obviously in top output.
You could try the "ps" technique, though that might suffer from the same limitation that top does. No harm in trying though. From the command line, do something like:
user% for ((i=0; i<30; i++)); do
for> ps alx >> ps.out
for> echo "\n=====\n" >> ps.out
for> sleep 1
for> done
Then look through your results in the "ps.out" file at the CPU column. Maybe you'll see something in there. That column is the %cpu -- from the ps man page:
   %cpu   The CPU utilization of the process; this is a decaying average over up to a minute
     of previous (real) time. Because the time base over which this is computed varies
     (some processes may be very young), it is possible for the sum of all %cpu fields to
     exceed 100%.