The Nagios Remote Plugin Executor (NRPE) allows your Nagios Enterprise Monitoring Server to communicate with the Linux machines on your server to determine things like free disk space, CPU load, and detect possible issues that a simple ping can't determine.
There are countless instructions online to download tar.gz files and install manually, or use a PPA to install via apt-get, but you'll be surprised to note the needed packages are in fact already in your Debian (and by proxy, Ubuntu) repositories.
To install the needed NRPE client on Debian / Ubuntu / other Debian-based Linux operating systems:
apt-get install nagios-nrpe-server nagios-plugins
Don't forget that you need to be root (Debian) or use sudo (Ubuntu).
Next, we just have to tell NRPE that it's allowed to communicate with our Nagios server. On the client system, open the file /etc/nagios/nrpe.cfg
Find the line that reads:
Now there are a few ways we can allow our server. First (and most obvious) is to add its IP address like this:
Where 192.168.0.5 is our Nagios/NEMS server.
Alternatively we can tell NRPE that it's allowed to communicate with any local system:
Now, save the file and restart NRPE as follows:
systemctl restart nagios-nrpe-server
If you have a software firewall running on your Linux machine, setup an exception for your NEMS server IP to gain access through ports 5666 and 12489.
And there we have it! Your Nagios/NEMS server should now be able to see your Linux machine.
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