Comparison · Open-Source Monitoring
Open-source monitoring, judged by what it costs to run
The license is free. The hours are not. This table compares the open-source monitors we see most in small and mid-size shops, plus one commercial yardstick.
Every open-source monitoring project looks similar on its feature page: discovery, templates, alerting, dashboards, an API. The differences show up six months in, when the history database has quietly grown to 200 GB, the one person who understood the config has changed teams, and a minor-version upgrade wants a schema migration during business hours. That is the lens we use on this page. We care less about the longest feature list and more about how much of your week the monitor itself will consume.
Zabbix, Nagios Core, Icinga, Checkmk (in its GPL Raw edition) and LibreNMS are all mature, all used in production by organizations far larger than a typical reader’s, and all capable of paging you at 3 a.m. for the right reasons. They differ in where configuration lives (a SQL database, text files, a DSL, rules in a web UI), in how they store metrics (SQL tables, RRD files, an external time-series database), and in how they scale beyond a single box. Those three design choices decide most of the operational cost.
We include PRTG in the table as a commercial reference point. It is not open source, but it is the product many teams price against before deciding that a self-hosted stack is worth the effort. If your honest answer is that nobody on the team wants to own a monitoring server, that comparison matters. How we review and score is written up on our methodology page.
How we score: read our methodology. Table order follows how often we recommend each product for this job, not any commercial arrangement.
The comparison table
6 products side by side
| Product | License | Runs on | Key feature | Best for |
|---|---|---|---|---|
| ZabbixZabbix | AGPLv3 (since 7.0; GPLv2 before) | Linux server; agents for Linux, Windows, macOS, BSD | Low-level discovery plus proxies for remote sites | Mixed estates that want one self-hosted tool for servers and network gear |
| Nagios CoreNagios Enterprises | GPLv2 | Linux / Unix server; checks via plugins, NRPE or SSH | Plugin model that thousands of community checks follow | Small, stable estates run by admins comfortable with text configs |
| IcingaIcinga GmbH | GPLv2 | Linux server; agents for Linux and Windows | Config DSL with apply rules, zones for distributed setups, REST API | Teams leaving Nagios who want automation and HA without paying per host |
| CheckmkCheckmk GmbH | GPLv2 (Raw) + commercial editions | Linux server (Debian, Ubuntu, RHEL, SLES), appliance or container | Agent-driven service discovery with rule-based configuration | Admins who want sensible defaults fast and may pay for scale later |
| LibreNMSLibreNMS community | GPLv3 | Linux server (PHP, MariaDB, RRDtool); optional distributed pollers | SNMP auto-discovery across a very wide list of device operating systems | Network teams with lots of switches, routers and firewalls to graph |
| PRTG Network MonitorPaessler | Commercial subscription | Self-managed on Windows Server, or PRTG Hosted Monitor (SaaS) | Sensor-based monitoring with auto-discovery and ready-made maps | Windows-centric teams that want a supported product and fast onboarding |
Every name links to our full review. Licensing and platform details reflect vendor documentation at the time of writing; confirm current terms on each vendor’s site.
Before you shortlist
How to choose
- Where configuration lives. Database-backed config (Zabbix, LibreNMS) is easy to change from a browser but harder to review; text or DSL config (Nagios, Icinga) fits Git and code review but punishes typos. Pick the one your team will actually keep tidy.
- Metric storage and growth. Ask how history is stored and how it is pruned. SQL history needs housekeeping or partitioning; RRD files stay a fixed size but lose detail; external time-series stores add another service to patch and back up.
- Scaling path. One server handles hundreds of hosts for every tool here. Past that, check whether the project scales with proxies, satellites or distributed pollers, and whether those remote pieces survive a WAN outage without losing data.
- Template and check quality. Good out-of-the-box templates save weeks. Look at what ships for your actual gear: Linux, Windows, your switch vendor, your hypervisor. A tool with fewer but better defaults often beats one with thousands of community checks of uneven quality.
- Upgrade rhythm. Read the last two major release notes before committing. Frequent releases with long-term support branches are a good sign; migrations that require stopping the server or rewriting configs are a cost you will pay every year or two.
A note on “free”
All five open-source projects can be used without a license fee, and several companies behind them sell support subscriptions or paid editions. Budget for the server, the storage and — most of all — the time of whoever owns the system. A monitor nobody maintains becomes a source of noise rather than signal. If that owner does not exist, a commercial product with vendor support may be the cheaper choice, and it is fine to say so.
Further reading
Head-to-head comparisons
Questions we get
FAQ
Which open-source monitoring tool is easiest to get running?
By most accounts Checkmk Raw gives the quickest first useful dashboard, because its agent discovers services on each host automatically. LibreNMS is similarly quick for network gear over SNMP. Zabbix and Icinga take longer to set up but give more control once tuned.
Is Nagios Core still worth choosing in 2026?
For a small, stable estate where someone already knows it, yes — it is light and dependable. For a new deployment we usually suggest Icinga or Checkmk, which keep compatibility with Nagios plugins while adding automation, clustering and a modern interface.
How much hardware does an open-source monitoring server need?
For a few hundred hosts with one-minute checks, 4 vCPUs, 8–16 GB of RAM and fast SSD storage is a sensible starting point. Storage is the variable to watch: history retention and polling interval affect disk growth far more than host count alone.
Can open-source monitoring replace a commercial product?
Technically, usually yes. The trade is money for time: you give up vendor support and polished onboarding, and in return you get no per-device fees and full control. Teams without a clear owner for the monitoring server often regret the switch.
Do these tools monitor cloud services too?
Yes, through agents on cloud VMs, HTTP and API checks, and in several cases vendor-maintained integrations for AWS, Azure or Kubernetes. Depth varies by project, so check the template or plugin for the specific service you rely on.
Disclosure. Scannethub is independent and hosts no software. Product links go directly to each vendor’s official site, and none of them earns us anything. No vendor pays for table order or verdicts. Details on ouraffiliate disclosure page.