Book excerpt: This book will introduce Nagios to readers who are interested in monitoring their systems. All the concepts in the book are explained in a simplified manner, presented in an easy-to-understand language with lots of tips, tricks, and illustrations. This book is great for system administrators interested in using Nagios to monitor their systems. It will also help professionals who have already worked with earlier versions of Nagios to understand the new features of Nagios 4 and provides usable solutions to real-life problems related to Nagios administration. To effectively use this book, system administration knowledge is required. If you want to create your own plug-ins, knowledge of scripting languages like Perl, shell and Python is expected.