I was testing some MySQL puppet modules on my Vagrant box earlier this week and one of them required augeas.
I kept running into "Could not find a default provider for augeas", however all the appropriate augeas , augeas-lib and ruby-augeas packages were installed. I inspected the different ruby directories and the files were perfectly in /usr/lib/ruby/site_ruby/1.8 where I expected them.
With all the files seemd to be in the right place, my next option was to strace a small ruby script that included augeas, guess what that showed ..
Indeed ... vagrant throws the default ruby to /opt/ruby .. and obviously there were no ruby-augeas files in there.