If you have an working Nagios Core monitoring server and some Linux machines (physical or virtual) you might want or even need to monitor their state. Nagios is a cool and free solution that makes this quite simple.
After you have deployed Nagios Core 4.0.x and up as a monitoring host you need to install monitoring daemon on Linux hosts. I have managed to monitor multiple Linux hosts with Nagios Core. All my Linux hosts run Debian or Ubuntu and this quick guide is based on Debian (wheezy).
Let’s start :)
1. Login to the Linux host you want to monitor, change to root:
user@nagios:~$ sudo -s