title: yarn no longer present
body: <p>Been running my <code>npm start</code>, which uses <code>yarn</code>, over and over for the last 5 months and has been working since day dot.  I even see it in my Terminal history 10 lines above.</p>
  
  <pre><code>&gt; yarn
  
  yarn install v1.10.1
  </code></pre>
  
  <p>I killed my <code>npm start</code> process a moment ago, and now for some reason, I get this...</p>
  
  <pre><code>&gt; yarn
  
  sh: yarn: command not found
  </code></pre>
  
  <p>Yarn is no longer installed on my system...for some reason.  So I installed it and get the usual information that it's installed.</p>
  
  <pre><code>$ npm -g install yarn
  + yarn@1.12.3
  added 1 package in 2.786s
  </code></pre>
  
  <p>But yarn still isn't installed and I'm still getting the same above issue.</p>
  
  <p>I haven't done anything that would have messed up <em>yarn</em> in anyway (no installing/updating/removing of any packages), so I'm completely stumped as to what the heck happened.</p>
  
  <p>Has anyone had this issue, know what it is and has a fix?</p>