Chapter 24. Writing Your Own Plugins
Plugins are independent programs—called by Nagios—that perform a check and return the result in standardized form. If there is neither a standard plugin for the task you want to perform, nor something appropriate in Categories | Check Plugins on NagiosExchange, then the best solution is for you to write a plugin yourself.
The plugin needs only to be executable on the command line, and to return a short text output for the admin and a standardized return value. If you want to make it available on the Internet as well, you need to comply with various guidelines so that it will be widely used and accepted without the need for extensive support.
There is no restriction in theory on the programming language used. ...