What’s the best way to monitor multiple Linux servers for configuration errors, high load or other problems? The answer is Nagios, which is a fantastic (and free!) networking monitoring system that lets you track multiple servers (HTTP, SMTP, SSH and more) across multiple machines, all backed by a neat user interface. More here

First of all we’ll tackle getting the central Nagios server set up, and enable reporting via the web front-end. You can install from source from www.nagios.org, or there should be a package available for your system. For Debian, this is the nagios2 package (not nagios, which is the old version), and you should also install nagios-plugins (we’ll talk about plugins later). On setup, it’ll ask you for the admin password – remember this! – and whether you want version 1 backwards compatibility (there’s no need for this if you’re performing a new setup).