HDFS-10601. Improve log message to include hostname when the NameNode is in safemode. Contributed by Kuhu Shukla.

(cherry picked from commit ba62b50ebacd33b55eafc9db55a2fe5b4c80207a)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -115,6 +115,7 @@ import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.lang.management.ManagementFactory;
 import java.net.InetAddress;
+import java.net.InetSocketAddress;
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -541,6 +542,8 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
 
   private INodeAttributeProvider inodeAttributeProvider;
 
+  private String nameNodeHostName = null;
+
   /**
    * Notify that loading of this FSDirectory is complete, and
    * it is imageLoaded for use
@@ -1099,6 +1102,9 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
       dir.setINodeAttributeProvider(inodeAttributeProvider);
     }
     snapshotManager.registerMXBean();
+    InetSocketAddress serviceAddress = NameNode.getServiceAddress(conf, true);
+    this.nameNodeHostName = (serviceAddress != null) ?
+        serviceAddress.getHostName() : "";
   }
   
   /** 
@@ -1370,7 +1376,7 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
 
   private SafeModeException newSafemodeException(String errorMsg) {
     return new SafeModeException(errorMsg + ". Name node is in safe " +
-        "mode.\n" + safeMode.getTurnOffTip());
+        "mode.\n" + safeMode.getTurnOffTip() + " NamenodeHostName:" + nameNodeHostName);
   }
 
   boolean isPermissionEnabled() {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestSafeMode.java

@@ -304,6 +304,30 @@ public class TestSafeMode {
     }
   }
 
+  @Test
+  public void testSafeModeExceptionText() throws Exception {
+    final Path file1 = new Path("/file1");
+    DFSTestUtil.createFile(fs, file1, 1024, (short)1, 0);
+    assertTrue("Could not enter SM",
+        dfs.setSafeMode(SafeModeAction.SAFEMODE_ENTER));
+    try {
+      FSRun fsRun = new FSRun() {
+        @Override
+        public void run(FileSystem fileSystem) throws IOException {
+          ((DistributedFileSystem)fileSystem).setQuota(file1, 1, 1);
+        }
+      };
+      fsRun.run(fs);
+      fail("Should not succeed with no exceptions!");
+    } catch (RemoteException re) {
+      assertEquals(SafeModeException.class.getName(), re.getClassName());
+      GenericTestUtils.assertExceptionContains(
+          NameNode.getServiceAddress(conf, true).getHostName(), re);
+    } catch (IOException ioe) {
+      fail("Encountered exception" + " " + StringUtils.stringifyException(ioe));
+    }
+  }
+
   /**
    * Run various fs operations while the NN is in safe mode,
    * assert that they are either allowed or fail as expected.