I’ll assume you already have Nagios installed and configured and have an understanding of actually configuring and using Nagios.

Remote server — the server to be monitored

First we’ll install the needed plugins and daemon on the remote server.

sudo apt-get install nagios-plugins nagios-nrpe-server

Once installed, open up /etc/nagios/nrpe_local.cfg

And place the following in it

allowed_hosts=NAGIOS.SERVER.IP,127.0.0.1

command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_all_disks]=/usr/lib/nagios/plugins/check_disk -w 20 -c 10
command[check_zombie_procs]=/usr/lib/nagios/plugins/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib/nagios/plugins/check_procs -w 150 -c 200
command[check_swap]=/usr/lib/nagios/plugins/check_swap -w 20 -c 10

Save and exit.

Commands need to explicitly be enabled on the …