In this chapter, we learned the basics of Nagios as a tool for performing system monitoring. It can be used to ensure that services are working correctly, problems are detected earlier, and appropriate people are aware when something's wrong.

We learned the basic types of objects in Nagios— commands, hosts, services, time periods, contacts, as well as object grouping. We have also found out about notifications and escalations, which can be used to notify administrators about problems.

The chapter also introduced the concept of dependencies that helps in understanding the root cause of complex problems.

We also learned the most important changes that Nagios 4 brings and how they can be used.

The next chapter will guide us through the process of setting up and configuring Nagios and the standard Nagios plugins.