State monitoring is the task of keeping track of the current status of network devices. A networking device’s state could be in different phases such as being available or unreachable.
In order to understand how Nagios achieves state monitoring, it’s important to look at key terms used with Nagios and to comprehend how Nagios uses them.
Nagios by itself is actually quite small. Nagios’s use of plug-ins provides the breadth of its functionality. A plug-in is an external application that Nagios calls to perform a specific task, such as checking the status of a host or service. Because there’s a plethora of hardware and software out there, Nagios cannot possibly be written to support each type, so it relies on plug-ins to provide that support. Nagios has a standard plug-in library, which is maintained by the Nagios Plug-in Project. (http://nagiosplug.sourceforge.net) You can obtain other plug-ins written by other people as well. A good source for additional plug-ins is Nagios Exchange (www.nagiosexchange.org).
Nagios constantly needs to know the state of a host or service. The process is called a check; with Nagios, a check tends to come in two forms:
Used when Nagios executes a plug-in to have it check a host or service. Depending on the response from the plug-in, Nagios updates the host or service’s status information. Nagios performs active checks at regular intervals defined in the configuration files. When Nagios performs ...