title: How to know whether Spark is running in standalone mode or running on Yarn?
body: <p>In my cluster sever, Spark is already being deployed.
  (Someone has set ip up and left quite a long time ago)</p>
  
  <p>I want to know whether Spark is running in standalone mode or running on Yarn.</p>
  
  <p>How can I check it?</p>