I love Nagios, It’s the first monitoring service I started using and I loved it since the beginning.

I love it because no matter people say it’s simple, it’s reliable, it’s predictable, it’s simple to reproduce every check Nagios is doing and check yourself the results.

During the years I tried several other software, but I always found them inferior to Nagios, they were too bulky, too chaotic and too disorganized.

Since last autumn I finally was able to get back to my good old Nagios at work, I upgraded it, and I expand it to check new services, check the old ones in a better way and make the setup easier and easier.

I would like to start a new project to share how I use it, which checks I do, and hopefully show someone that the good old Nagios still has some arrows to shoot :)

Let’s start with a check I love and I never found in any other monitoring software: check_reboot_required

This check warns you if there’s a new kernel on you GNU/Linux machine that requires a reboot, it basically extract the running kernel version and the last kernel installed on the server, if they don’t match and the running kernel is older it turns on a warning alert, very simple and very effective to keep your server updated and secure.

Obviously this check is very important if you constantly run automatic updates (via yum-cron, dnf-automatic or unattended upgrades).

The check was written by Johan Ryberg and you can find it in his Github repo, It works perfectly fine on any RedHat based distribution and also on any Debian based distribution, I suggested a small change to make it works with Amazon Linux 2 also.

To use it you only have to

1. place the check_reboot_required file on the server you want to monitor in the Nagios plugins directory (/var/lib64/nagios/plugins on RHEL based distributions or /var/lib/nagios/plugins on Debian based distributions)

2. add this simple command to the nrpe config file (/etc/nagios/nrpe.conf) and restart the nrpe service.

command[check_reboot]=<NAGIOS PLUGINS PATH>/check_reboot_required -s $ARG1$

3. add the “Reboot required” service to your host in the Nagios server configuration

define service{
use generic-service
host_name server.domain.tld
service_description Reboot required
check_command check_nrpe!check_reboot!w
}

4. restart Nagios and enjoy