Keeping an eye on cpu usage of your servers is one of the basic things in system monitoring. For Nagios (and Shinken, of course) you’ll find plenty of plugins for this task. However, i was never happy with the way they work. Most of the plugins you can download work like this: read a counter - sleep - re-read the counter. This technique not only adds an extra delay to the execution time of the plugin, but it only shows the state of things within a small time frame. If you run such a plugin every 5 minutes and it sleeps 5 seconds between the two measurements, you don’t know what happens in the other 295 seconds. This is a very small sample rate.