Problem scenario: You are trying to use gem install, but you get an error like this:
mkmf.rb can't find header files for ruby at /usr/lib/ruby/ruby.h"
Solution: Install ruby-devel. For RedHat deriviatives, you can find the rpm here.
Problem scenario: You are running gem install *.gem, and you get 'ERROR: While executing gem ...
(Net::HTTPServerException) 407 "Proxy Authentication Required"'
Potential Solutions: The server's Internet connection seems to be somewhat working (but not completely and not completely broken either). Change your proxy settings. Your proxy seems to be causing an issue. It could potentially help to disable the proxy to eliminate Internet access. It may help to reboot the server that you ran the gem install command on.