The complexity of modern networks and systems is somewhat astounding, as any experienced System Administrator will tell you. Even seemingly small networks found in many Small/Medium Enterprises (SME’s) can have extremely high levels of complexity in the systems they run.
Nagios was designed as a rock solid framework for monitoring, scheduling and alerting. Nagios contains some very powerful features, harnessing them is not only a matter of understanding how Nagios works, but also how the system you’re monitoring also works. This is an important realization. Nagios can’t automatically teach you about complex systems, but it will be an valuable tool to help you in your journey.
So what are the sorts of things Nagios can do? Nagios can do much more than this, but nevertheless here’s a list of common things that Nagios is used for.
Check to see if a server is up and running
Notify you if a server is down (by email/pager/SMS)
Check to see if a service is running (mail, http, pop, ssh)
Check to see if a process (or Windows service) is running
Gather performance statistics on a server
Allow specific alerts to only go to particular groups/individuals
Get reports of downtime on your servers
The Nagios package doesn’t contain any checking tools (called plugins) at all. Does that statement sound crazy? Sure, but let me explain. Nagios focuses on doing what it does best - providing a robust, reliable and extensible framework for any type of check that a user can come up with.
So how does Nagios perform it’s checking? A huge number of plugins already exist that extend Nagios to perform every type of check imaginable. And if there isn’t an existing check that already exists, you’re free to write your own. The nagios-plugins package is separately maintained and can be downloaded from various sources. We will cover the Nagios plugins later on.
Ethan Galstad is the creator of Nagios. Karl DeBisschop, Subhendu Ghosh, Ton Voon, and Stanley Hopcroft are the main plugin developers. Many other people have contributed to the project over the years by submitting bug reports, patches, ideas, suggestions, add-ons, plugins, etc. A list of some of the contributors can be found at the Nagios website.