title: How to enable Debug level logging in Log4J (in Hadoop)
body: <p>I see a lot of code with the following check in Hadoop:</p>
  
  <p>if (LOG.isDebugEnabled()) {
   ...</p>
  
  <p>I guess this is related with log4j? How can I enable Debug level logging in Hadoop? </p>
  
  <p>I see a log4j property file in conf directory of Hadoop and I see some lines like these:</p>
  
  <p># Custom Logging levels</p>
  
  <p>hadoop.metrics.log.level=INFO</p>
  
  <p>#log4j.logger.org.apache.hadoop.mapred.JobTracker=DEBUG
    #log4j.logger.org.apache.hadoop.mapred.TaskTracker=DEBUG
    #log4j.logger.org.apache.hadoop.fs.FSNamesystem=DEBUG</p>
  
  <p>So is this a matter of uncommenting some entries here I guess? </p>