Welcome to where the rubber meets the road. Until now, I’ve talked a lot about how Nagios works and how it is installed and configured. This chapter ties together the theoretical work of the previous chapters and talks about the nitty gritty of performing systems monitoring. As I’ve repeatedly said throughout the book, Nagios is a scheduling and notification framework. Small, single-purpose programs called plug-ins do the monitoring. So an in-depth discussion about monitoring will mostly be a discussion about plug-ins.