title: Xvfb not found on your system
body: <p>I try to use Xvfb to make the headless code run. However, I encountered the problem that "Xvfb not found on your system" when I tried to run my ruby code. Then I tried to install Xvfb using</p>
  
  <pre><code>sudo apt-get install xvfb
  </code></pre>
  
  <p>However, "apt-get: command not found" is showed. Thus, I have not idea what should be installed to avoid the original Xvfb error. Any helps? Thank you.</p>