Failed to Build Gem Extension Error Installing rails
<p>I'm on a fresh Ubuntu installation and using the guide to install rails found <a href="http://railsapps.github.io/installrubyonrails-ubuntu.html" rel="nofollow">here</a>.</p>

<p>When I get to the final <code>sudo gem install rails</code>, I get this error:</p>

<pre><code>    Building native extensions.  This could take a while...
ERROR:  Error installing rails:
    ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/2.3.0/gems/nio4r-1.2.1/ext/nio4r
/usr/bin/ruby2.3 -r ./siteconf20160821-19665-u7rxlt.rb extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.3.0/gems/nio4r-1.2.1 for inspection.
Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/nio4r-1.2.1/gem_make.out
</code></pre>