Nagios

Good system administrators know about problems long before anyone asks, „Hey, is the Internet down?“ Nagios, an open source system and network monitoring tool, has emerged as a popular and affordable choice for sys admins in organizations of all sizes. It´s robust but also complex. Nagios: System and Monitoring, written for Nagios 2.0, but backwards compatible with earlier versions, will help you take full advantage of this program´s ability to keep systems running.
Nagios, which runs on Linux and most *nix variants, can be configured to continuously monitor network services (SMTP, POP3, HTTP, NNTP, PING, and so on), host resources (processor load, disk and memory usage, running processes, log files, and so on), and environmental factors (such as temperature). This book is your guide to getting the most out of this versatile and powerful administration tool.
Inside Nagios: System and Network Monitoring, you´ll learn how to:

-Install and configure the Nagios core, all standard Nagios plug-ins, and selected third-party plug-ins -Write your own plug-ins to customize Nagios for your unique environment -Configure problem escalation so the appropriate people are notified when issues move beyond your control, and suppress alerts during scheduled maintenance periods -Program event handlers to take action when trouble occurs -Monitor Windows servers
Written by a seasoned author of books on advanced networking topics.