Even given the very useful standard plugins in the Nagios Plugins set, and the large number of custom plugins available on Nagios Exchange, occasionally as our monitoring setup grows more refined, we may find that there is some service or property of a host that we would like to check, but for which there doesn't seem to be any suitable plugin available. Every network is different, and sometimes the plugins that others have generously donated their time to make for the community don't quite cover all your bases. Generally, the more specific your monitoring requirements get, the less likely it is that there's a plugin available that does exactly what you need.

In this example, we'll deal with a very particular problem that we'll assume can't be dealt with effectively by any known Nagios Core plugins, and we'll write one ourselves using Perl. Here's the example problem:

Our Linux security team wants to be able to automatically check whether any of our servers...