Nagios Initial Configuration: Key Options and Setup Tips

Setting up a robust monitoring system is crucial for maintaining the health and performance of your IT infrastructure. Nagios, a widely used open-source monitoring tool, offers a comprehensive solution for monitoring the availability and status of network resources, services, and hosts. In this tutorial, we’ll guide you through the essential steps of configuring Nagios for effective monitoring.

Prerequisites and Installation

Before diving into the configuration process, ensure you have the necessary prerequisites in place. You’ll need a Linux server with root access, Apache, PHP, and a mail transfer agent installed. Once your prerequisites are met, you can proceed to install Nagios. We recommend using the source code installation method for greater flexibility and control over the setup process.

Configuring Nagios Core

1. Understanding Configuration Files

Nagios configuration relies on a set of files that define how monitoring is performed. These files are typically located in the /usr/local/nagios/etc directory. Key files include nagios.cfg, which contains the main configuration, and object configuration files such as hosts.cfg and services.cfg. These files define what and how Nagios monitors.

2. Defining Hosts and Services

In the hosts.cfg file, you’ll define the hosts you want to monitor. Each host entry includes information like the host’s address, display name, and monitoring templates. The services.cfg file lets you specify services to monitor on each host, such as HTTP, SSH, or database services.

3. Setting Up Contacts and Notifications

Nagios can alert specific contacts when issues are detected. Configure contact information, such as email addresses and pager numbers, in the contacts.cfg file. Additionally, define contact groups to categorize and manage notifications efficiently.

Configuring Monitoring Plugins

1. Understanding Plugins

Nagios plugins are executables or scripts that perform the actual monitoring tasks. These plugins are defined in the commands.cfg file and are associated with specific service checks. You can use built-in plugins or create custom ones to suit your monitoring needs.

2. Creating Custom Plugins

If the built-in plugins don’t cover your monitoring requirements, you can develop custom plugins using languages like Bash, Python, or Perl. These plugins should follow a specific output format for Nagios to interpret the results correctly.

Web Interface and Visualization

1. Accessing the Nagios Web Interface

The Nagios web interface provides a user-friendly way to visualize monitoring data, acknowledge alerts, and manage configurations. By default, it’s accessible through a web browser using the server’s IP address or domain name.

2. Navigating the Web Interface

The web interface presents an overview of hosts, services, and their statuses. It allows you to acknowledge alerts, schedule downtime, and view historical data. Understanding the layout and navigation options is crucial for efficient monitoring.


Setting up Nagios for initial configuration involves understanding its core components, defining hosts and services, configuring notifications, and utilizing plugins. With this foundation, you’ll be well-equipped to monitor your IT environment effectively and ensure the reliability and availability of your resources and services. Remember that Nagios offers extensive customization options, so you can tailor your monitoring setup to fit your organization’s specific needs.

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