title: Failed to build gem native extension when install RedCloth-4.2.9 install Linux
body: <p>I want to install <code>Octopress</code> in my computer.
  I try to do it like </p>
  
  <p><a href="http://octopress.org/docs/setup/" rel="noreferrer">Octopress document.</a></p>
  
  <p>When I run</p>
  
  <pre><code>bundle install
  </code></pre>
  
  <p>I got error message</p>
  
  <pre><code>An error occured while installing RedCloth (4.2.9), and Bundler cannot continue.
  Make sure that `gem install RedCloth -v '4.2.9'` succeeds before bundling.
  </code></pre>
  
  <p>So, I run</p>
  
  <pre><code>sudo gem install RedCloth -v '4.2.9'
  </code></pre>
  
  <p>then, I got a error message again:</p>
  
  <pre><code>ERROR:  Error installing RedCloth:
  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:1:in `&lt;main&gt;'
  </code></pre>
  
  <p>I hadn't learn any knowledge about ruby.</p>