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EnglishWhat Is Nagios and What Does It Do?
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Nagios is a free, open-source IT monitoring platform, built around Nagios Core and licensed under the GPL. It watches servers, networks, applications, and cloud infrastructure by actively polling them, so you can see whether devices are healthy, services are available, and performance is within expected bounds. It is self-hosted, meaning you install and run it on your own infrastructure rather than using it as a vendor-hosted service. It is a reasonable thing to look into if you want monitoring you control and can extend, and a poor fit if you want a fully managed service with no server to maintain.
What Nagios monitors
The project groups its coverage into several areas:
- Servers — device health and resource behavior
- Networks — reachability and availability of network devices
- Applications — service availability and application-level checks
- Cloud platforms — monitoring across cloud infrastructure
- Databases and metrics — performance and system metrics collection
The mechanism behind all of this is active polling: the monitoring host periodically checks each target and records the result. That is what produces the status you act on — up, down, degraded, or slow.
Nagios Core and the wider product family
Nagios Core is the foundation: the free, open-source, self-hosted monitoring engine. Everything else in the ecosystem either extends it or packages it for a different audience.
The site also points to a Nagios Core Services Platform and a CSP Upgrade path, along with commercial offerings such as Nagios XI for enterprise system and metrics monitoring. In practice this means you have two broad routes:
| Route | What you get | Who it suits |
|---|---|---|
| Nagios Core | Free, GPL-licensed, self-hosted monitoring engine | Teams comfortable installing, configuring, and maintaining their own monitoring stack |
| Commercial offerings (e.g., Nagios XI) | Enterprise-oriented monitoring with vendor support | Organizations that want supported tooling and less self-assembly |
The upgrade link on the site is the entry point if you want to move from the community edition toward the commercial side. Pricing details are not specified in the material available here, so treat cost as something to confirm directly before committing.
Why people choose it
- Longevity — the project describes 25+ years of history, so there is a large body of documentation, plugins, and community knowledge behind it.
- Self-hosted and open source — your monitoring data and configuration stay on infrastructure you control, and the GPL license means you can inspect and extend the code.
- Community — the project explicitly highlights its community as part of its value, which matters when you need help with an unusual check or integration.
- Breadth — one system covering servers, networks, applications, and cloud reduces the number of separate tools you have to run.
What to check before you commit
- Hosting and maintenance burden. Self-hosted means you own installation, upgrades, and uptime of the monitoring server itself. Confirm you have someone to do that.
- Which edition fits. Decide up front whether Core's free engine is enough or whether you need the supported commercial path. The site's upgrade page is the place to compare.
- Cost and licensing specifics. The material here confirms free, open-source, GPL-licensed Core, but does not state commercial pricing. Verify current terms on the site rather than assuming.
- Your actual targets. List the servers, network devices, applications, and cloud services you need covered, then confirm each can be polled the way you expect.
If your goal is simply to understand the landscape, the short version is: Nagios is a mature, self-hosted, open-source monitoring system that polls your infrastructure and reports on health, availability, and performance — with a free core and commercial options layered on top.