Nagios on a Rasp Pi 3 with NEMS

Small but Mighty

Generating a Configuration File

The first step in generating a configuration file is to define the devices and services you want to monitor. After connecting to the server from a web browser, the default page shows information about the server's status and has a menu with links to all of the NEMS components (Figure 2).

Figure 2: NEMS default page.


Creating and maintaining Nagios configurations is traditionally very time consuming, and the process is prone to errors. NEMS addresses these issues with an updated version of NConf [4] called NEMS Configurator. This application is found on the Configuration menu and is used to automate the generation of Nagios3 configurations. To access, log on using the user ID and password that you entered during the nems-init process.

A few hosts and services are defined to get you started. You can use these as examples when you are building the configuration for your environment. Once you have defined the hosts and service to be checked, click on the Generate Nagios config link, and NConf will attempt to build a configuration file for Nagios3 (Figure 3).

Figure 3: NConf with highlighted Deploy link after generating a Nagios config with no errors or warnings.

If all goes well, you will receive no errors or warnings. If you see any errors, the Deploy link will not be available. You should investigate any warnings and decide whether you want to continue with deployment of the updated configuration; click the Deploy button, and NConf sends a request to Nagios3 to load the new configuration file.

NConf is no longer being developed by the original authors. Version 1.4 was developed and is supported by Robbie Ferguson for NEMS. Despite this, you can find helpful information on the original authors' website.


To review the status of checks done by Nagios3, you can use the JSON output of the included Nagios API or use one of the three reporting applications available by selecting Reporting : Nagios Core [5], NagVis [6], and Check_MK [7]. Each provides a different view of the Nagios3 monitoring data.

Nagios Core is an event scheduler, event processor, and alert manager for monitored devices and services (Figure 4). Detailed information about Nagios Core is available on the project's website.

Figure 4: Nagios Core tactical overview page.

NagVis visualizes Nagios3 data and displays IT processes (e.g., an email system or a network infrastructure) as mapped objects (Figure 5). Using back-end data, NagVis updates these objects periodically to reflect their status. These maps also allow you to arrange objects and display them in different layouts.

Figure 5: NagVis Hosts view.

The nems-init process does not set the logon ID and password for this application. The first time you log on to NagVis, you use admin as the default for both the username and password. After logging on, you should use the change password option under User menu to change it.

I find I do most of my real-time monitoring with the Check_MK tool. This application has a very good overview of the status of hosts and services (Figure 6). It is updated often, and the graphics provide a great view of current issues, as well as those from the past four hours that have been resolved.

Figure 6: Example of the Check_MK Overview.

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