title: Is there documentation for Airflow log file return codes?
body: <p>I am trying to identify what in a .log file makes a specific task marked as "Successful" vs "Failure" in airflow. I am getting the sense that this is dependent upon the operator (<code>PythonOperator</code> vs <code>EmailOperator</code> vs <code>BashOperator</code> etc.). </p>
  
  <p>I am seeing different return codes. For example, <code>INFO - Task exited with return code 1</code> or <code>INFO - Task exited with return code 0</code> or <code>INFO - Process psutil.Process(pid=00000, status='terminated') (00000) terminated with exit code -15</code></p>
  
  <p>I am not seeing consistency.. I first thought <code>INFO - Task exited with return code 0</code> constituted a success, but I see some failure logs also have this.</p>
  
  <p>I would appreciate any insight into understanding different return code #.</p>