The most exciting aspect of using Nagios is the ability to combine your programming skills with the powerful engine offered by the Nagios daemon. Your own pieces of code can be plugged into the Nagios daemon, and they can communicate with it in various ways.

One of the best things about Nagios is that, in most cases, it does not force you to use a specific language. Whether the language of your choice is PHP, Perl, Tcl, Python, Ruby, or Java, you can easily use any one with Nagios. This is a fundamental difference between Nagios and the majority of monitoring applications. Usually, an application can only be extended in the language in which it is written.

Our code can cooperate with Nagios in various ways, for example, by implementing commands, by sending information to the Nagios daemon, and so on. The first case means that we can create a script or executable that will be run by Nagios, and its output and exit code will be processed by Nagios. Running external...