HDFS-8551. Fix hdfs datanode CLI usage message. Contributed by Brahma Reddy Battula.

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

@@ -903,6 +903,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-8548. Minicluster throws NPE on shutdown.
     (surendra singh lilhore via xyao)
 
+    HDFS-8551. Fix hdfs datanode CLI usage message.
+    (Brahma Reddy Battula via xyao)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -262,9 +262,11 @@ public class DataNode extends ReconfigurableBase
     LogFactory.getLog(DataNode.class.getName() + ".clienttrace");
   
   private static final String USAGE =
-      "Usage: java DataNode [-regular | -rollback]\n" +
+      "Usage: hdfs datanode [-regular | -rollback | -rollingupgrade rollback" +
+      " ]\n" +
       "    -regular                 : Normal DataNode startup (default).\n" +
       "    -rollback                : Rollback a standard or rolling upgrade.\n" +
+      "    -rollingupgrade rollback : Rollback a rolling upgrade operation.\n" +
       "  Refer to HDFS documentation for the difference between standard\n" +
       "  and rolling upgrades.";