One of the most important challenges in system monitoring is to detect and report any malfunctioning system or device as soon as possible, so that you as an administrator are aware of the problem before a user runs into one. Nagios is a powerful monitoring tool that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes. It monitors your entire IT infrastructure to ensure systems, applications, services, and business processes are functioning properly. In the event of a failure, Nagios can alert the technical staff of the problem, allowing them to begin remediation processes before outages affect business processes, end-users, or customers. Learning Nagios 4 is a practical, beginner-level book that introduces you to setting up Nagios and walks you through all the basics of configuring it. It will guide you through the process of getting Nagios 4 up and running, using the web interface and monitoring IT systems. This book will also help you with understanding the typical problems encountered in setting up large-scale Nagios environments, as well as guide you through creating your very own Nagios plug-ins. Learning Nagios 4 will introduce Nagios to the system administrators who are interested in monitoring their systems as well as networks. This book starts by guiding you through setting up and configuring your first instance of Nagios so you can quickly start using it to ensure your IT is working properly. The book also covers using SNMP to monitor various network-enabled devices. You will also find out how to use NSClient++ to monitor Microsoft Windows systems. The book explains distributed monitoring using multiple Nagios instances. Also, if you want to create your own plug-ins for Nagios, this book will teach you how to do so using programming languages like C and scripting languages like PHP, Perl, shell and Python. By the end of this book, you will have all the necessary knowledge you need to set up Nagios 4 as well as for using Nagios in a large, distributed environment that monitors a large number of computers, services, and devices. 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.