Nagios is a host and service monitor designed to inform you of network problems before your clients, end-users or managers do. It has been designed to run under the Linux operating system, but works fine under most *NIX variants as well (We have run it on Solaris 2.8 and now Solaris 10). The monitoring daemon runs intermittent checks on hosts and services you specify using external "plugins" which return status information to Nagios. When problems are encountered, the daemon can send notifications out to administrative contacts in a variety of different ways (email, instant message, SMS, page etc.). Current status information, historical logs, and reports can all be accessed via a web browser. A wap interface is also available.

Unlike the reactive snmp trap catching paradigm (HP Openview, Netcool, etc), Nagios is a proactive monitoring tool designed to actively check each host of each type for the status of those services that you care about. i.e. Windows hosts can be pinged, but Unix boxes can be pinged and checked for ssh health. Whilst many plugins exist and can be downloaded, you are empowered to write your own checks in the language of your choice, the only formatting required being the STDOUT status message that is returned.