Graphs make numerical data more accessible; or, as Edward R. Tufte puts it: "Graphics reveal data." [1] The Munin monitoring application is known for drawing simple and practical graphs. This helpful tool, which is named for a mythical raven who delivers news to the Norse god Odin, collects, stores, and plots data in daily, weekly, monthly, and annual charts (Figure 1).

Figure 1: Munin generates daily, weekly, monthly, and annual graphs.

Munin, a GPLed monitoring tool originally developed by the Norwegian Linux service provider Linpro [2], receives data through a system of plugins tailored for various monitoring activities. A collection of useful plugins come pre-bundled with the Munin monitoring tool, and other plugins are available from third-party sources on the Internet. However, if you are faced with a monitoring task that other users haven't imagined yet, you might need to create your own plug-in. The very extensible Munin lets you create custom plugins for monitoring a wide range of activities. In this article, I'll explain how to build a plugin that monitors airport departures and arrivals.

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