title: Rails Tutorial: nokogiri-1.5.2 error on bundle install
body: <p>After working through the RVM setup, rspec and guard sections of chapter 3 of the <a href="http://ruby.railstutorial.org/chapters/static-pages">Ruby on Rails Tutorial</a>, whenever I run <code>bundle install</code> I get the following error dump:</p>
  
  <pre><code>Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
      /usr/bin/ruby1.9.1 extconf.rb 
  /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
  from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
  from extconf.rb:5:in `&lt;main&gt;'
  
  
  Gem files will remain installed in /home/dan/.bundler/tmp/17577/gems/nokogiri-1.5.2 for inspection.
  Results logged to /home/dan/.bundler/tmp/17577/gems/nokogiri-1.5.2/ext/nokogiri/gem_make.out
  An error occured while installing nokogiri (1.5.2), and Bundler cannot continue.
  Make sure that `gem install nokogiri -v '1.5.2'` succeeds before bundling.
  </code></pre>
  
  <p>In the gem_make.out:</p>
  
  <pre><code>Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
      /usr/bin/ruby1.9.1 extconf.rb 
  /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file --mkmf (LoadError)
  from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
  from extconf.rb:5:in `&lt;main&gt;'
  </code></pre>
  
  <p>I've been debugging for a while now and I think I'm stuck. Help would be GREATLY appreciated!</p>