First, let's learn about Nagios. We will discuss setting up Nagios, how to add hosts to Nagios, how to make use of templates in Nagios, and how to set up services using hostgroups. We will also see how to use Nagios for alerts, write our own plugins to monitor, the NPRE plugin for Nagios, and how to execute Nagios from external machines.
Nagios provides you with a web-based interface and once it is set up correctly, you can monitor your system centrally. It gives you information and you can control that as well. Nagios uses very less resources and hence it's low on maintenance. Setting up Nagios is easy: install it on a server and add all the clients that you want to monitor. Nagios service does the work of checking whether the clients are reachable using Ping or SSH, whether HTTP/LDAP/NFS are working, and so on. The beauty of this is you need not install any special software or packages on the client machines that are being monitored.
Let's see how we can install Nagios...