title: How can one debug/get logs for failures of the SparkR Java backend?
body: <p>I'm bedeviled by a <code>No status is returned. Java SparkR backend might have failed.</code> error when fitting a glm using Spark.  The job actually appears to run to completion based on the Spark web ui, but at some point during model fit (it doesn't appear to be a consistent location), SparkR returns the above error message and then returns to the R REPL.  I'm not seeing a log anywhere I can refer to in order to identify the problem.  Would the Question Answerer point me towards the log, or provide other feedback regarding this problem?</p>
  
  <p>I can see that the error generating code is <a href="https://github.com/apache/spark/blob/master/R/pkg/R/backend.R" rel="noreferrer">here</a>.  It looks as though perhaps the connection specified by <code>get(".sparkRCon", .sparkREnv)</code> just isn't there or responds spuriously with an empty string during computation?  I'm at a loss.</p>
  
  <p>I'm on Spark <code>2.0.0</code> using Amazon EMR <code>5.0</code>.</p>