Nagios

Nagios (/ˈnɑːɡiːoʊs/) is an open-source network and infrastructure monitoring system. It monitors hosts, services, and network devices, sending alerts when components fail and again when they recover. Originally written by Ethan Galstad in 1999 as NetSaint, it was renamed Nagios in 2002 after a trademark dispute. The name is a recursive acronym: "Nagios Ain't Gonna Insist On Sainthood."

Nagios uses a plugin-based architecture: the core scheduler runs check plugins at configured intervals, processes the results, and triggers notifications. Hundreds of community-developed plugins exist for monitoring specific services and hardware. Nagios is written in C and runs on Linux and other Unix systems. It is licensed under the GPLv2.

Galstad founded Nagios Enterprises in 2007 to provide commercial support and the proprietary Nagios XI product. The project's plugin-architecture model influenced several derivative projects, including Icinga (2009), Shinken (2009), Naemon (2013), and Checkmk.