The material below just illustrates the logic behind adding a remote host for monitoring under Nagios. It does not do a step by step account on how to add a remote host. Reason being is because one must understand the basic logic behind these configuration files. If the logic is not grasped then big miss configurations are bound to happen.
There are several configuration files that need consideration. If you have performed a manual install of NAGIOS Core the configuration files will reside under /usr/local/nagios/etc/
The main configuration file for Nagios is /usr/local/nagios/etc/nagios.cfg Under that file the location of the OBJECT Configuration files is defined. Below is the default structure of these configuration files.
# OBJECT CONFIGURATION FILE(S) cfg_file=/usr/local/nagios/etc/objects/templates.cfg cfg_file=/usr/local/nagios/etc/objects/contacts.cfg cfg_file=/usr/local/nagios/etc/objects/commands.cfg cfg_file=/usr/local/nagios/etc/objects/timeperiods.cfg cfg_file=/usr/local/nagios/etc/objects/localhost.cfg cfg_file=/usr/local/nagios/etc/objects/windows.cfg cfg_file=/usr/local/nagios/etc/objects/switch.cfg cfg_file=/usr/local/nagios/etc/objects/printer.cfg