Nagios Core — The Classic That Still Runs
General Information
Nagios Core is one of those tools that refuses to disappear. It’s been around since the early 2000s, and in many networks it’s still running quietly in the background. The idea is simple: check if something is alive, complain if it’s not. It doesn’t look modern and never tried to, but the stability and the ocean of plugins keep it relevant.
How It Works
Nagios does its job in cycles. It pings a host, runs a check on a port, or executes a script — if the result looks bad, it raises an alert. Everything is defined in text configs, which feels old-school but also gives total control. Passive results from external scripts are accepted too. The power comes from plugins: if you can script a check, Nagios can monitor it.
Functions You Actually Get
Function | What It Means |
Host & service checks | Ping, ports, processes, custom scripts. |
Plugin system | Thousands of ready checks, or write your own. |
Alerts | Email, SMS, chat — whatever you wire in. |
Event handling | Run actions automatically when failures happen. |
Extensions | Works with add-ons like Icinga, Centreon, Nagios XI. |
Installation Notes
It’s not a one-click install. On Debian/Ubuntu you pull in build tools, Apache, PHP, then compile from source. Create the nagios user, set permissions, configure Apache with CGI. After that, start the service and add your host configs in /usr/local/nagios/etc/objects/. RHEL/CentOS is much the same. Once you know the steps, it’s routine, but for first-time users it can feel clunky.
Real-World Use
In small shops, Nagios Core is often used as-is: watch a handful of servers, maybe a switch or two, and send an email if something dies. In larger companies, it’s the “engine under the hood” for other tools. Centreon, Icinga, even commercial Nagios XI — they all build on top of it to provide dashboards and easier configs. The real win is flexibility: if you can test it from the command line, Nagios can keep an eye on it.
Drawbacks
It shows its age. The web interface is barebones. Configs are text-only and can get messy. No built-in graphs or time-series data, so for trends you’ll need add-ons. It’s an engine, not a full suite.
Comparison
Tool | Platforms | Strengths | Best Fit |
Nagios Core | Linux/Unix | Proven, huge plugin base, stable | Small to mid networks, labs, legacy setups |
Icinga 2 | Linux/Unix | Modern fork, distributed checks, REST API | Enterprises needing flexible setups |
Zabbix | Linux/Windows | All-in-one with alerts + dashboards | Larger infrastructures |
Prometheus | Multi-platform | Cloud-native, metrics-first approach | Containers and Kubernetes clusters |