I have installed Nagios 2.11 through APT Package Manager on the Ubuntu server to monitor the freeBSD. Installed NRPE 2.11 on both Ubuntu and the freeBSD server as daemon and client respectively.
Installed Nagios Plugins v1.4.11 on both servers.
I have setup and configured NRPE on both servers and seems to be working fine. On the Ubuntu monitoring server, I can manually run the check_nrpe command for the remote server :-
/usr/lib/nagios/plugins/check_nrpe -H xxx.xx.xxx.xxx -c check_load
This command returns the following :-
OK - load average: 0.18, 0.14, 0.11|load1=0.177;15.000;30.000;0; load5=0.140;10.000;25.000;0; load15=0.114;5.000;20.000;0;