I was recently contacted by Packt Publishing and asked to review their book Instant Nagios Starter, by Michael Guthrie. I've actively used Nagios (and forks) for well over a decade now, and have even contributed some code development to it, so I'm intimately familiar with installing, configuring, and managing Nagios environments.
Nagios is an extremely powerful and flexible monitoring platform, and those two attributes also result in it also being a fairly complex piece of software to configure if you've never dealt with it before. This book does an excellent job of walking you through the steps of installation and basic configuration of Nagios on a CentOS/RHEL system.
Nagios, as with just about any complex piece of software, relies on a number of system configuration settings, files in multiple locations, etc. to run properly. Instant Nagios Starter does an excellent job of walking you through each and every dependency so that you can get a basic Nagios server up and running in no time at all. If you're new to Nagios, or need to spin up a new Nagios server and may have only ever worked with existing Nagios setups in the past, then this guide will save you a lot of time and potential aggravation in getting started.
The title of this book is extremely accurate - it will get you started with Nagios in almost no time at all. If you're looking for anything beyond the basics of setting up Nagios then you'll want something a bit more in depth, and Packt Publishing has you covered there as well since they also have a number of other books on the subject.
Perhaps the only thing that would make this book more valuable would be if Packt Publishing offered a download of a VMWare CentOS instance with Nagios pre-installed (or partially installed) for those who don't want to waste any time installing linux first.