Nagios is a popular open source computer system and network monitoring software application. Nagios, originally created under the name NetSaint, was written and is currently maintained by Ethan Galstad, along with a group of developers actively maintaining both official and unofficial plugins. N.A.G.I.O.S. is a recursive acronym: “Nagios Ain’t Gonna Insist On Sainthood”.
Nagios offers today complete monitoring and alerting for servers, switches, applications, and services. A commercial version, Nagios XI, extends now those services to build an enterprise-class Open Source component.