Nagios Still Works, But Do You Have Time for It?

Nagios has been around since 1999. That's not a dig; it's genuinely impressive. Most software from that era is either dead or unrecognizable, but Nagios is still running in production at thousands of organizations, doing exactly what it was designed to do. There's something to be said for a tool that's been battle-tested for over two decades.

But "it works" and "it's the right choice for you in 2026" aren't the same thing. Nagios was built in an era when servers were pets, not cattle, and when having a dedicated sysadmin who could spend days configuring monitoring was normal. If that's still your situation, Nagios might genuinely be the right call. If it's not, you should probably look elsewhere.

Full disclosure: this is the FiveNines blog, so I'm obviously not a neutral party here. I'll try to be fair about where Nagios makes sense, but factor in the bias accordingly.

What you're signing up for with Nagios

Nagios Core is free and open source, which sounds great until you realize what "free" actually costs. The software itself costs nothing. The time to set it up, configure it, maintain it, write plugins for things it doesn't monitor out of the box, update those plugins when they break, and debug configuration file syntax errors at 2am: that's not free.

The Nagios model is essentially "here's a framework, build what you need." Want to monitor a specific service? There might be a community plugin, or you might need to write one. Want a custom alert condition? Edit the configuration files. Want to change how something displays? More configuration files. The flexibility is real, but so is the complexity.

For organizations with dedicated infrastructure teams who have the time and expertise to build out a monitoring system exactly to their specifications, this model works. Nagios becomes a platform you customize endlessly to fit your exact needs. Some people genuinely enjoy this, and the results can be impressive.

For everyone else, it's a time sink that never quite gets finished. You set up basic monitoring, it works, then you need to add something new and suddenly you're three hours deep in documentation trying to figure out why your check script isn't being recognized. The monitoring system that's supposed to reduce your operational burden becomes part of the operational burden.

The web interface hasn't helped Nagios' reputation either. It's functional in the sense that it shows you information, but "functional" is about the kindest word for it. If you're used to modern web applications, the Nagios UI feels like stepping back in time. Some people don't care about this (the data matters, not the presentation), but if you're going to stare at a dashboard regularly, aesthetics do affect usability.

Where FiveNines takes a different approach

FiveNines started from a different premise: monitoring should work out of the box. Install the agent (one command), point it at your servers, and you immediately get CPU, memory, disk, load average, and process metrics without configuring anything. If you're running Docker containers or Proxmox VMs, those get picked up automatically too.

The trade-off is flexibility. Nagios lets you monitor literally anything if you're willing to write the plugin. FiveNines monitors what it's built to monitor. For most server and infrastructure monitoring needs, what's built in covers it. If you have exotic requirements that fall outside the standard metrics, you'll hit limits that Nagios wouldn't have.

Cron job monitoring is built into FiveNines in a way that Nagios doesn't attempt natively. Your scheduled jobs ping FiveNines when they run, and if they don't ping within the expected window (with configurable grace periods), you get an alert. It's a simple feature, but it catches the kind of silent failures that basic uptime monitoring misses entirely.

The dashboard situation is reversed from Nagios. FiveNines has a modern interface with drag-and-drop customization and the ability to create public status pages. Whether that matters depends on how you work. If you live in terminals and treat web UIs as necessary evils, this is irrelevant. If you actually use dashboards for monitoring and want to share them with teammates or clients, the difference is noticeable.

The real cost comparison

Nagios Core is free. FiveNines has a free tier for 5 servers and paid plans starting at $5/month for 30 servers. On paper, Nagios wins on price.

In practice, the comparison is messier. Nagios Core requires you to host it somewhere, which means a server (with its own costs and maintenance), or a VM, or a container that you're responsible for keeping running. You need someone with the skills to set it up, and you need ongoing time to maintain it. If you value your time at anything above zero, "free" starts looking expensive.

Nagios XI, the enterprise version with better UI and support, starts around $1,995 per license. At that point, you're definitely not in "free" territory anymore, and the comparison with SaaS pricing looks different.

FiveNines costs money but requires no infrastructure and no maintenance. Whether that trade-off makes sense depends entirely on your situation. If you already have infrastructure expertise in-house and a server sitting around with spare capacity, the SaaS cost might feel unnecessary. If you're a small team trying to focus on building product rather than maintaining monitoring systems, the SaaS model pays for itself in time saved.

The plugin ecosystem question

Nagios has thousands of community plugins accumulated over two decades. Whatever you want to monitor, someone has probably written a plugin for it. This is a genuine advantage if you have niche requirements.

The flip side is that community plugins have varying quality, documentation, and maintenance status. Some are excellent and actively maintained. Some were written in 2009 and haven't been touched since. Some work great until they don't, and then you're debugging someone else's Perl script. The ecosystem is huge but uneven.

FiveNines doesn't try to compete on plugin breadth. It monitors servers, containers, VMs, common databases (PostgreSQL, Redis), web servers (Nginx, Caddy), and a few other integrations. If your needs fit within that scope, everything works together coherently. If you need to monitor something obscure that FiveNines doesn't support, you're either out of luck or supplementing with another tool.

Making the choice

Nagios makes sense if you have a team with strong Linux and sysadmin skills, you genuinely need the flexibility to monitor arbitrary things with custom plugins, you prefer self-hosted solutions for security or compliance reasons, and you have the time budget to invest in setup and ongoing maintenance.

FiveNines makes sense if you want monitoring working today rather than next month, your needs fit within standard server and infrastructure metrics, you'd rather pay money than spend time on configuration and maintenance, and you don't have (or don't want to use) dedicated infrastructure staff for monitoring.

Some organizations run both: Nagios for legacy systems with custom monitoring requirements that have been refined over years, and something lighter for newer infrastructure where the standard metrics are sufficient. There's no rule that says you can only have one monitoring tool.

The worst outcome is choosing Nagios because it's "free" and then never actually getting it configured properly, so your monitoring is perpetually half-finished and unreliable. If you're not going to invest the time Nagios requires, you're better off with something that works out of the box, even if it costs money.