diff --git a/Dockerfile b/Dockerfile
index 5332b3d3..d07f1b55 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,6 +16,7 @@ RUN wget https://github.com/kiwenlau/compile-hadoop/releases/download/2.7.2/hado
 # set environment variable
 ENV JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64 
 ENV HADOOP_HOME=/usr/local/hadoop 
+ENV HADOOP_CLASSPATH=/usr/lib/jvm/java-7-openjdk-amd64/lib/tools.jar
 ENV PATH=$PATH:/usr/local/hadoop/bin:/usr/local/hadoop/sbin 
 
 # ssh without key
diff --git a/README.md b/README.md
index 1ea382b1..00159f0a 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,13 @@ cd hadoop-cluster-docker
 sudo ./start-container.sh
 ```
 
+
+If you want to keep the data from your previous launch
+
+```
+sudo ./start-container-preserved.sh
+```
+
 **output:**
 
 ```
diff --git a/start-container-preserved.sh b/start-container-preserved.sh
new file mode 100755
index 00000000..4231aa39
--- /dev/null
+++ b/start-container-preserved.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+
+# the default node number is 3
+N=${1:-3}
+
+
+# start hadoop master container
+echo "start hadoop-master container..."
+sudo docker run -itd \
+                --net=hadoop \
+                -p 50070:50070 \
+                -p 8088:8088 \
+                --name hadoop-master \
+                --hostname hadoop-master \
+                kiwenlau/hadoop:1.0 &> /dev/null
+
+
+# start hadoop slave container
+i=1
+while [ $i -lt $N ]
+do
+	echo "start hadoop-slave$i container..."
+	sudo docker run -itd \
+	                --net=hadoop \
+	                --name hadoop-slave$i \
+	                --hostname hadoop-slave$i \
+	                kiwenlau/hadoop:1.0 &> /dev/null
+	i=$(( $i + 1 ))
+done 
+
+# get into hadoop master container
+sudo docker exec -it hadoop-master bash