title: Trouble installing passenger gem on Ubuntu
body: <p>From the console:</p>
  
  <pre><code> adelevie@ubuntu:~$ gem install passenger
      Building native extensions.  This could take a while...
      ERROR:  Error installing passenger:
          ERROR: Failed to build gem native extension.
  
      /usr/bin/ruby1.8 extconf.rb
      /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require': no such file to load -- mkmf (LoadError)
          from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
          from extconf.rb:8
  
  
      Gem files will remain installed in /home/adelevie/ruby/gems/gems/fastthread-1.0.7 for inspection.
      Results logged to /home/adelevie/ruby/gems/gems/fastthread-1.0.7/ext/fastthread/gem_make.out
  </code></pre>
  
  <p>What does this mean and what are my options?</p>