NP, many miss this very same thing. francesco has it right, so he must not have missed the message reported during the make install command he issued. There are several other flavors of the "make something" like "make install-init" I think is another one. That will install the init scripts so nagios starts up automatically upon system reboot. So, if in doubt, just run make install again, and this time, READ what is at the end of that output. It will have told you to run " make install-config" just as fronacesco pointed out.