Introducing plugins & there use in monitoring.

Nagios uses plugins to monitor service or group of services (known as service groups). Plugins are basically scripts or executables, which when executed provides an output that is passed to the Nagios server to check with the mentioned or stated output (configured at the time of configuring service). If the output matches then Nagios will change the service “status” as defined in the service_check component.

For every service a special plugin is defined by Nagios itself and also custom plugins can be created and implemented if required.