Nagios is a free, open-source, and powerful monitoring tool that helps you to monitor your entire IT infrastructure, servers, services, and applications from the central location. It is based on a client-server architecture, so you will need to install the Nagios agent on the client system and add it to the Nagios server for monitoring. If you are looking for a monitoring solution, then Nagios is an essential tool for any production server environment. Is there a way to do it by yourself? Of course, there is. In this tutorial, we will show you how to install Nagios 4 and monitor your server on Ubuntu 20.04.