Nokogiri won't install? Check that you have accepted Xcode's EULA
An non obvious reason for being unable to install updates to Nokogiri
Here is a pro tip I never thought I would need to share!
For Nokogiri to install on OSx out of the box it requires some of the command line tools that come with xCode. I have everything like that installed because I have had to install things like Nokogiri several times in the past.
Today though I was getting this error message that suggested that I didn't have those required tools installed.
Building native extensions. This could take a while... Building nokogiri using packaged libraries. ERROR: Error installing nokogiri: ERROR: Failed to build gem native extension. /Users/tobyosbourn/.rvm/rubies/ruby-2.1.1/bin/ruby extconf.rb Building nokogiri using packaged libraries. checking for iconv.h... *** extconf.rb failed *** Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options.
10 minutes of yak shaving later and I decided to open up xCode to see what the craic was, turns out a point release had been downloaded and installed and came with a new EULA, as soon as I accepted this I was able to install the nokogiri gem successfully!