I just had the following error while trying to start Smokeping on one of my newly installed machines:
ERROR: fping (‘/usr/bin/fping -C 1 localhost’) could not be run: localhost address not found
After digging around somewhat (this worked fine when run on the commandline) turns out my /etc/hosts was chmodded 700 instead of 744. Weird, but this meant only root could resolve it. What I don’t understand is why this did not work – my resolvers also return 127.0.0.1 for the “localhost” query.
Anyway, if you get this error, check if the smokeping user can resolve localhost too 
As Kris would say, it was some sort of DNS problem…