OpenNMS: what it is
OpenNMS Horizon is a free, open-source network monitoring platform. It combines fault, performance and traffic monitoring with alarms and notifications for local and distributed networks. It collects data over SNMP, JMX, HTTP, Prometheus and other standard protocols without third-party plugins, receives NetFlow, IPFIX and sFlow, and can measure service latency from remote locations with lightweight Minion collectors.
It is built for larger networks and teams that want one system for availability, performance graphs and alarms. We have not run OpenNMS ourselves (Not tested yet); this page summarises the official repository and documentation.
OpenNMS at a glance
| Item | Details |
| Developer | The OpenNMS Group and community (GitHub: OpenNMS/opennms) |
| Latest version | Horizon 36.0.5, released on GitHub on 14 October 2026 |
| Platforms | Linux servers: RHEL and CentOS Stream, Debian, Ubuntu; container deployment on Kubernetes or OpenShift |
| Requirements | A supported Java Development Kit and PostgreSQL database; minimum 2-core x86_64 CPU, 4 GB RAM, 50 GB disk (16 GB RAM and a quad-core CPU recommended) |
| Licence | Free, open source: AGPL v3 |
| Last verified | 28 October 2026, against the OpenNMS GitHub repository and its documentation sources |
Main features
- Provisioning and inventory: automatic discovery plus requisitions that can be fed from configuration management tools.
- Performance data: collection over SNMP, JMX, HTTP and Prometheus, with graphs and thresholds.
- Flows and BGP: NetFlow, IPFIX and sFlow traffic analysis and BGP monitoring.
- Alarms and notifications: event correlation into alarms, with notification paths and escalation.
- Distributed monitoring: Minions monitor remote sites; Sentinels and Kafka or ActiveMQ help scale processing.
- Dashboards and reports: customisable dashboards with PDF export and topology maps.
How to get started
Install Horizon from the OpenNMS package repositories on a supported Linux distribution, set up PostgreSQL and the JDK, then run the installer and start the service as described in the official installation guide. For a quick non-production trial, the project points to evaluation install scripts in the opennms-forge/opennms-install repository; Docker images (opennms/horizon) are also published. Plan RAM and disk for the number of nodes and metrics you collect.
Related tools
If you mainly need to know which switch port a device uses, the lighter Netdisco may be enough. For a commercial Windows-based monitoring suite with sensor-based licensing, see PRTG.
Limitations to know
- Linux server only; no Windows server version.
- A sizeable Java application: plan time for setup, tuning and upgrades.
- Horizon is the fast-moving community edition; the OpenNMS Group also offers a separately supported edition (Meridian) for organisations that want longer release cycles.
FAQ
Is OpenNMS free?
Yes. OpenNMS Horizon is open source under the AGPL v3 and free to use.
What is the latest OpenNMS version?
On 28 October 2026 the latest Horizon release on GitHub was 36.0.5, published on 14 October 2026.
Does OpenNMS run on Windows?
The server does not; it runs on Linux or in containers. You can monitor Windows machines from it, and use the web interface from any browser.
How much hardware does OpenNMS need?
The documented minimum is a 2-core x86_64 CPU, 4 GB of RAM and 50 GB of disk; 16 GB of RAM and a quad-core CPU or better are recommended.