HDFS-8226. Non-HA rollback compatibility broken (Contributed by J.Andreina)

(cherry picked from commit e01c1a979c)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/bin/start-dfs.sh
	hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsUserGuide.md

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

@@ -428,6 +428,8 @@ Release 2.7.1 - UNRELEASED
     HDFS-7980. Incremental BlockReport will dramatically slow down namenode
     startup.  (Walter Su via szetszwo)
 
+    HDFS-8226. Non-HA rollback compatibility broken (J.Andreina via vinayakumarb)
+
 Release 2.7.0 - 2015-04-20
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/bin/start-dfs.sh

@@ -30,18 +30,18 @@ HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
 . $HADOOP_LIBEXEC_DIR/hdfs-config.sh
 
 # get arguments
-if [ $# -ge 1 ]; then
-	nameStartOpt="$1"
+if [[ $# -ge 1 ]]; then
+  startOpt="$1"
   shift
-	case "$nameStartOpt" in
-	  (-upgrade)
+  case "$startOpt" in
+    -upgrade)
+      nameStartOpt="$startOpt"
     ;;
-	  (-rollback) 
-	  	dataStartOpt="$nameStartOpt"
+    -rollback)
+      dataStartOpt="$startOpt"
     ;;
-	  (*)
-		  echo $usage
-		  exit 1
+    *)
+      hadoop_exit_with_usage 1
     ;;
   esac
 fi

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsUserGuide.md

@@ -318,7 +318,9 @@ When Hadoop is upgraded on an existing cluster, as with any software upgrade, it
 
     * stop the cluster and distribute earlier version of Hadoop.
 
-    * start the cluster with rollback option. (`bin/start-dfs.sh -rollback`).
+    * run the rollback command on the namenode (`bin/hdfs namenode -rollback`).
+
+    * start the cluster with rollback option. (`sbin/start-dfs.sh -rollback`).
 
 When upgrading to a new version of HDFS, it is necessary to rename or delete any paths that are reserved in the new version of HDFS. If the NameNode encounters a reserved path during upgrade, it will print an error like the following: