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, or 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, or Java, you can easily use it with Nagios. This is a fundamental difference between Nagios and the majority of monitoring applications. Usually, an application can only be extended in the same language it is written in.

Our code can cooperate with Nagios in various ways — either by implementing commands or by sending information to the Nagios daemon. The first case means that we create a script or executable that will be run by Nagios, and its output and exit code is then processed by Nagios. Running external commands is used for performing active checks, sending...