HDFS-6694. TestPipelinesFailover.testPipelineRecoveryStress tests fail intermittently with various symptoms - debugging patch (Contributed by Yongjun Zhang)

(cherry picked from commit c5d9a4a91e4e0faae3a8530408da35b591396060)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestPipelinesFailover.java

@@ -55,6 +55,7 @@ import org.apache.hadoop.test.GenericTestUtils;
 import org.apache.hadoop.test.GenericTestUtils.DelayAnswer;
 import org.apache.hadoop.test.MultithreadedTestUtil.RepeatingTestThread;
 import org.apache.hadoop.test.MultithreadedTestUtil.TestContext;
+import org.apache.hadoop.util.Shell.ShellCommandExecutor;
 import org.apache.log4j.Level;
 import org.junit.Test;
 import org.mockito.Mockito;
@@ -414,6 +415,33 @@ public class TestPipelinesFailover {
    */
   @Test(timeout=STRESS_RUNTIME*3)
   public void testPipelineRecoveryStress() throws Exception {
+
+    // The following section of code is to help debug HDFS-6694 about
+    // this test that fails from time to time due to "too many open files".
+    //
+    String[] scmd = new String[] {"/bin/sh", "-c", "ulimit -a"};
+    ShellCommandExecutor sce = new ShellCommandExecutor(scmd);
+    sce.execute();
+
+    System.out.println("HDFS-6694 Debug Data BEGIN===");
+    System.out.println("'ulimit -a' output:\n" + sce.getOutput());
+
+    scmd = new String[] {"hostname"};
+    sce = new ShellCommandExecutor(scmd);
+    sce.execute();
+    System.out.println("'hostname' output:\n" + sce.getOutput());
+
+    scmd = new String[] {"ifconfig"};
+    sce = new ShellCommandExecutor(scmd);
+    sce.execute();
+    System.out.println("'ifconfig' output:\n" + sce.getOutput());
+
+    scmd = new String[] {"whoami"};
+    sce = new ShellCommandExecutor(scmd);
+    sce.execute();
+    System.out.println("'whoami' output:\n" + sce.getOutput());
+    System.out.println("===HDFS-6694 Debug Data END");
+
     HAStressTestHarness harness = new HAStressTestHarness();
     // Disable permissions so that another user can recover the lease.
     harness.conf.setBoolean(