Common Nagios Errors and What to Do about Them

Common Nagios Errors and What to Do about Them

Table of Contents


Nagios is an open-source monitoring system that has become indispensable for system administrators and DevOps teams across the world. However, like any other software, you’re bound to come across errors with Nagios. In this article, we’re going to take a look at some common errors and how to solve them, along with the pros and cons of Nagios, and why MetricFire is the perfect alternative for monitoring.


You can learn more about MetricFire by booking a demo or signing up for the free 14-day trial


Pros and cons of using Nagios

Nagios allows you to monitor a variety of critical infrastructure components, including network infrastructure, systems metrics, network protocols, operating systems, services, and applications. It provides a complete view of an organization’s business processes and network. And while it provides a lot of benefits, it comes with its fair share of drawbacks. 



  • With Nagios, you can set up notifications for different conditions, like performance degradation and service outages, to prevent downtime.

  • There’s a range of community-contributed and third-party plugins that cover nearly all use cases, so you can find a plugin for monitoring your applications and services.

  • This tool helps increase the availability of your applications and services and find server outages, network outages, and protocol failures.  



  • Nagios has a steep learning curve, and figuring out how to configure and set it up can be quite a challenge. The interface can also be confusing. 

  • Scaling Nagios for larger infrastructures is also quite complex, and you might have to manage multiple Nagios instances as your infrastructure grows.

  • Nagios primarily focuses on alerting and monitoring, so it’s not the best when it comes to advanced visualization.   

  • The UI can also be streamlined further and reports are not too in-depth.

  • The tool doesn’t provide bandwidth monitoring, and the free version is quite limiting.

  • Support is not free after the first year of your Nagios plan, and the pricing plans are quite expensive. 



Common Nagios Errors and their Solutions

You can come across numerous kinds of errors when working with Nagios, ranging from configuration errors, permission issues, and plugin errors to network issues, false positives, and incorrect alerts. Here are some of the most common Nagios errors, along with possible solutions.   


a. Hosts unreachable

One of the most common Nagios errors is when the host becomes unreachable. There can be numerous reasons for this, like network configurations or problems, and you can try out a few things to solve this error. 

First, check your network to make sure that the network connection to the host is stable and there are no issues with the firewall or routing. 

Then, review both the service and host definitions in the Nagios configuration files for inconsistencies and errors. You might have the notify_unreachable option in the host definition activated, causing you to see this error. If you don’t want to know when the host is unreachable, all you need to do is simply deactivate this option in the definition.    

Also, make sure that the host is up and running since in some cases, there can be a problem with the host, too.  


b. Return code of x is out of bounds

Nagios uses return codes from plugins in order to determine the state of hosts or services. If you see the error ‘Return code of x is out of bounds,’ it usually means one of two things:

  1. The path to your plugin is invalid, like the script doesn’t exist. You’re more likely to come across this error if the return value is 127. In this case, simply check the command definition to ensure the path is correct. 

  2. The plugin you’re using to check the host or service doesn’t return the correct return value as it terminates.

Some possible fixes you can try to resolve this issue are:

  • Check the plugin responsible for the error. Go through the documentation and the code to know the expected return codes. 

  • Make sure that the plugin configuration in your Nagios setup is right, including the range of expected return codes. 

  • If your plugin is causing issues or is outdated, try updating it or consider using an alternative. 


c. IndexError: list index out of range

You typically see this error when Nagios tries and fails to get information. This can be due to many reasons, like issues with a plugin, some misconfiguration, or even a syntax error in the configuration. To solve this problem, you can try out the following:

  • Go through the Nagios configuration files and pay close attention to the parameters related to the host or service responsible for the error. 

  • Take a look at the plugin causing the problem. Make sure it’s configured correctly and provides the expected data.  

  • Use debugging logs and tools to find the exact location of the error. Once you do that, you can easily troubleshoot the problem.  


d. Could not open command file for update

This error usually occurs when there’s some problem with file permissions or with the directory, and Nagios is unable to write to the command file (the file responsible for processing commands like scheduling downtime and acknowledging problems). To get rid of this problem, try this:

  • Make sure that a directory exists for the command file.

  • Check the permissions of both the command file and the directory containing it to make sure that the Nagios group or user has write access. 

  • Make sure you restart the web server so that it can recognize the updated group permissions that you have set. 

  • It’s also a good idea to check if there’s enough free space on the file system where Nagios stores the command file. 


Alternatives to Nagios

While Nagios is a powerful solution, it’s not the best option for everyone, especially SMEs and those who don’t have much experience with network and infrastructure monitoring. This is where MetricFire comes in



MetricFire is a modern monitoring platform that provides application, system, and infrastructure monitoring via various open-source monitoring tools. It provides Graphite-as-a-Service and allows you to see all your metrics on aesthetically pleasing and detailed dashboards made with Grafana. The key idea behind MetricFire is monitoring with a hosted solution with powerful monitoring capabilities that can help you understand your systems and their statuses at just a glance.


You can learn more about MetricFire by booking a demo or signing up for the free trial.  


Monitoring with a Hosted Setup 

MetricFire stands out with its ecosystem of infrastructure monitoring, which comprises Grafana and Graphite, some of the most famous open-source monitoring services. In addition to that, it includes preconfigured plugins for a variety of open-source projects, including collectd and StatsD. You get all of these in a hosted environment, and with the features of different open-source tools combined into one, you can benefit from lots of functionalities. 


With this innovative approach to monitoring, MetricFire is great for various use cases, including infrastructure monitoring, server monitoring, application monitoring, business intelligence, and network monitoring.  


a. Benefits of MetricFire

MetricFire has lots of great benefits, including: 

  • A very straightforward and user-friendly interface that can help you get started quickly

  • Robust technical support is provided by engineers, so you can get all the answers you need if you get stuck somewhere

  • The ability to easily create Grafana dashboards

  • Unlimited video conference and phone support from engineers regardless of your service level commitments 

  • Hosted monitoring and quick setup not only make things easy but also allow your employees to focus on innovation and other important tasks like developing, updating, and optimizing apps and systems while leaving monitoring to MetricFire 


b. Getting Started

Getting started with MetricFire is quite easy, and you can do it today. You can either book a demo and get a more tailored solution based on your monitoring needs, or you can sign up for a free 14-day trial and try out the platform yourself to see all that it offers. 



There’s no doubt that Nagios is a robust and famous network and infrastructure monitoring tool. However, it comes with its fair share of challenges like a steep learning curve, scalability issues, and complex setup. Not to mention, there are errors that you’re most likely to come across such as unexpected return codes and hosts becoming unreachable that might leave you frustrated. 


This is where MetricFire comes in. It’s quite easy to set up, offers excellent customer support, and provides all the benefits of open-source tools. With its hosted monitoring solution, ease of use, and advanced visualization thanks to Grafana, MetricFire addresses many shortcomings that are typically associated with Nagios.


If you can’t decide if it’s the right option for you, you can sign up for a free trial or book a demo.  

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