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Nagios Core

Nagios Core is the GPL-2.0 open-source monitoring engine behind Nagios, checking hosts and services with plugins and alerting when problems occur.

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Introduction

Nagios Core is the long-standing open-source monitoring engine at the heart of the Nagios ecosystem. It schedules checks on hosts and services through plugins, tracks state changes and sends notifications. Commercial Nagios XI builds on it.

The source code is at NagiosEnterprises/nagioscore on GitHub under the GPL-2.0 licence, with about 2,100 stars; the most recent commit was on 27 October 2026.

Features

  1. Plugin architecture: Thousands of community plugins.
  2. Host and service checks: Active and passive checks.
  3. Notifications: Escalations and contacts.
  4. Web interface: Status and history.
  5. Event handlers: Automated responses.

Pros

  1. Free to use: Open source under GPL-2.0.
  2. Maintained: Commits as recent as 27 October 2026.

Cons

  1. Dated UX: Configuration is file-based and verbose.
  2. Not cloud-native: Less suited to dynamic container environments.

Install Nagios Core and the Nagios plugins from packages, define hosts and services in configuration files, and restart Nagios to apply.

Resources:

Pricing

Nagios Core is free and open source under the GPL-2.0 licence.

  1. Traditional IT environments with stable hosts.
  2. Teams with existing Nagios plugins.
  3. Not a fit for dynamic Kubernetes workloads.

Conclusion

Nagios Core remains a reliable, plugin-rich monitoring engine for classic infrastructure.

Alternatives

Other tools on CheckOps that cover similar ground. Open a page, or compare one with Nagios Core side by side.