title: Trying to install a ruby gem and getting no-where
body: <p>I'm trying to install a gem in debian using </p>
  
  <pre><code>gem install typhoeus 
  </code></pre>
  
  <p>but I just keep getting this error message.  I've tried a few things but they obviously didn't work.  Could use some ideas, I'm new to both unix and ruby so go easy =)</p>
  
  <pre><code>root@asdf:/home/asdf# gem install typhoeus
  Fetching: ffi-1.9.3.gem (100%)
  Building native extensions.  This could take a while...
  ERROR:  Error installing typhoeus:
      ERROR: Failed to build gem native extension.
  
      /usr/bin/ruby1.9.1 -r ./siteconf20140719-30469-1rufzif.rb extconf.rb
  /usr/local/lib/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- mkmf (LoadError)
      from /usr/local/lib/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
      from extconf.rb:4:in `&lt;main&gt;'
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /usr/lib/ruby/gems/1.9.1/gems/ffi-1.9.3 for inspection.
  Results logged to /usr/lib/ruby/gems/1.9.1/extensions/x86-linux/1.9.1/ffi-1.9.3/gem_make.out
  </code></pre>
  
  <p>Here's the gem from github:
  <a href="https://github.com/typhoeus/typhoeus" rel="nofollow">https://github.com/typhoeus/typhoeus</a></p>