SysAdmin's Journey

Book Review: Learning NAGIOS 3.0 by Wojciech Kocjan

I was recently asked by PACKT Publishing to review the book Learning NAGIOS 3.0 by Wojciech Kocjan. I agreed to do so so long as I could state whatever I felt about the book, and PACKT was fine with that. I’m guessing they were fine with that because they knew the book was pretty darn good! Click through for a full chapter-by-chapter breakdown of the book. Learning Nagios
3.0.png Title: Learning NAGIOS 3.0 Author: Wojciech Kocjan ISBN: 978-1-84719-518-0 Overall, this is a good book, with material that everyone except the most seasoned Nagios veterans can appreciate. I myself have been using Nagios for about the last 10 years, and I’ve been too lazy to upgrade my 2.x install to the latest 3.x install. After reading the book, I think I’ll make it a priority. The book’s main audience is probably ideally someone who isn’t new to *nix, but is new to Nagios. They will get the most use out of this book. That being said, there was quite a bit of new information or tips that I hadn’t discovered on my own within the book as well. Perhaps what I liked most about the book is that not only did it tell you how to get things set up when you have only 10 hosts and 20 services to monitor, it told you how to set things up so that performance and manageability don’t become an issue when that same instance of Nagios is monitoring thousands of hosts and services. Here’s a quick breakdown of content by chapter. Note that Chapter 7 is clickable - you may download a PDF for free of that chapter.

Chapter 1: Nagios Overview

The author does a good introduction about the core ideas and conventions in Nagios, and at the end he offers a “What’s New” section for sysadmins who are upgrading from 2.x.

Chapter 2: Installation and Configuration

This chapter walks you through installing Nagios from source on Ubuntu ‘Gutsy’ 7.10. It also goes through the basic tasks of creating hosts, services, commands, time periods, contacts, and groups of objects. After getting your feet wet, the book dives into one of the key features of Nagios, inheritance. New to Nagios 3.0 is the capability to inherit from more than one parent, which is a welcome addition. The final section goes into one of the most important features (and one of the features Nagios implements best): notifications.

Chapter 3: Using the Nagios Web Interface

The first precursor to using the web interface is to get it setup properly. One key point that the book leaves out, and can be a major stumbling block for new users is that the core of the web interface is compiled C binaries. Most users expect PHP, Perl, or some other interpreted language, but this is not the case in Nagios. This severely limits the number of people who can go in and modify the web UI - everyone knows PHP, not many know C. The rest of the chapter goes through using the web interface to check status, print reports, etc.

Chapter 4: Overview of the Nagios Plugins

Each Nagios installation is only as good as it’s plugins. In fact, without any plugins, Nagios is unable to really do anything at all. Nagios' reliance upon plugins is one of the reasons that it’s been around for so long, and seems to fit everyone’s setup. Most use the same Nagios core, but you’d be hard pressed to find two installations using the exact same set of plugins. The majority of the chapter goes over the core plugins that are included in the Nagios Plugins distribution.

Chapter 5: Advanced Configuration

Chapter 5 covers some things that the Nagios docs don’t - mainly how to organize your definitions into a maintainable file and directory structure. It also goes into detail about the depth-first inheritance search order, and multiple inheritance - new to Nagios 3. Also new to Nagios 3, custom variables, are covered here as well. Chapter 5 also covers the algorithm used to determine flapping, and does it very well. I’d never comprehended it until reading the book.

Chapter 6: Notifications and Events

Note: This chapter has two abstracts available on PACKT’s website - you can read Part 1 here, and Part 2 here. This chapter goes over the ins and outs of setting up contacts properly. The key here is to not over-notify contacts about incidents they have no input or control on, because they will quickly delete or even filter all messages from Nagios. The chapter also goes into different types of notifications available to Nagios. When fixing a broken application’s source code is not an option, many times the only solution is to restart the application when it fails. Nagios can do this for you as well in what’s referred to as Event Handlers. This chapter walks you through setting up an event handler that restarts Apache should it die. New to Nagios 3 is Adaptive Monitoring. Adaptive monitoring gives you the ability to dynamically change configurations stored in the config files via the named pipe. The remainder of the chapter walks you through building, installing, and configuring NSCA to accept passive check results over the network.

Chapter 7: Passive Checks and NSCA

Chapter 7 starts the content with the subject of passive checks. Passive checks are the key to scaling Nagios to thousands of hosts. The author then goes into the pros and cons of active and passive checks. From there, you are taken through several examples of passive host and service checks.

Chapter 8: Monitoring Remote Hosts

This chapter introduces the reader to the concept of remote checks, and how they differ from passive checks. The first part of the chapter goes into detail about using SSH to execute remote checks. Personally, I have never used this approach, as it introduces a little more security risk - if someone were to compromise the nagios user account on the Nagios server, they would likely get shells on all your other servers as well. The next section of the chapter goes into setting up NRPE, which I personally recommend and use extensively. NRPE is has much less overhead than SSH, but still encrypts the connection. Also, NRPE is not a shell, so if the nagios user is compromised on the server, the only thing the attacker could do to the remote machines is run the previously defined service checks on your client hosts. The author walks the reader through examples of using both approaches.

Chapter 9: SNMP

SNMP is very near and dear to me - I was forced to love it when working with DOCSIS back in my cable industry days. The author gives a pretty good introduction to SNMP in the beginning of the chapter. After introducing the reader to net-snmp utilities and some GUI’s, he goes into detail about installing and testing the net-snmp agent on the remote hosts. Once SNMP is set up on the remote hosts, it’s time to start playing with the check_snmp plugin. check_snmp is not so different from other plugins, and is not bad to setup at all. One thing that I had tried before, and failed at doing, was setting up Nagios to be a SNMP trap destination. The author presents a way to do this, but I would argue that his method wouldn’t scale very well. Either way, his method works - although it’s important to remember that Nagios is not a SNMP management package.

Chapter 10: Advanced Monitoring

The first part of the chapter goes into using NSClient++ to monitor Windows systems. I would argue that this is not necessarily “Advanced Monitoring” - maybe there should be a small chapter dedicated to monitoring Windows. However, that’s all semantics - the content itself is accurate and well stated. The chapter goes into detail about installing NSClient++ and using check_nt, check_nrpe, and passive checks using NSCA to get data from your Windows hosts. The remainder of the chapter goes into distributed Nagios instances. I myself have never had to do this, but in reading through the content, it certainly looks doable. It appears as though there isn’t too much to the initial setup, but config file maintenance looks like it could become cumbersome. I’ll have to noodle on that for a bit!

Chapter 11: Extending Nagios

Yoda might have been quoted as saying “Only after a padawan writes plugins will the true power of Nagios be unveiled to him” - or maybe not, but it’s definitely a true statement. That’s what chapter 11 is all about - writing your own plugins. I can especially appreciate the fact that the author distinguishes between a working plugin, and a plugin written the right way. The chapter finishes up with how you might go about writing your own web interface (only skimming the surface for obvious reasons).


In summary, this book is for anyone who runs, or is thinking about running Nagios 3.0 for business or pleasure. It’s a pretty quick read, and has quite a bit of information in it that will have you reaching for it like you would a reference book. In the interest of full disclosure, all links to PACKT’s website from this article will result in me receiving referral dollars should you purchase the book from them. I only participate in referrals when I have personally used and approve of the product. If you enjoyed this review and are interested in purchasing the book, I would appreciate your referral.