title: java.io.IOException: Incompatible clusterIDs
body: <p>I am installing Hadoop 2.7.2 (1 master NN -1 second NN-3 datanode) and cannot start the datanodes!!!
  After trouble shouting the logs (see below), the fatal error is due to ClusterID mismatch... easy! just change the IDs.
  <strong>WRONG</strong>... when I check my VERSION files on the NameNode and the DataNodes they are identical.. </p>
  
  <p>So the question is simple: INTO the log file --> Where the ClusterID of the NameNode is coming From???? </p>
  
  <p>LOG FILE:</p>
  
  <hr>
  
  <pre><code>WARN org.apache.hadoop.hdfs.server.common.Storage: java.io.IOException: Incompatible clusterIDs in /home/hduser/mydata/hdfs/datanode: namenode clusterID = **CID-8e09ff25-80fb-4834-878b-f23b3deb62d0**; datanode clusterID = **CID-cd85e59a-ed4a-4516-b2ef-67e213cfa2a1**
  org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool &lt;registering&gt; (Datanode Uuid unassigned) service to master/172.XX.XX.XX:9000. Exiting.
  java.io.IOException: All specified directories are failed to load.
  atorg.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:478)
  atorg.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1358)
  atorg.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1323)
  atorg.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:317)
  atorg.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
  atorg.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:802)
  at java.lang.Thread.run(Thread.java:745)
  WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool &lt;registering&gt; (Datanode Uuid unassigned) service to master/172.XX.XX.XX:9000
  INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool &lt;registering&gt; (Datanode Uuid unassigned)
  WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
  </code></pre>
  
  <p>COPY of THE VERSION FILE </p>
  
  <hr>
  
  <p><strong>the master</strong></p>
  
  <pre><code>storageID=DS-f72f5710-a869-489d-9f52-40dadc659937
  clusterID=CID-cd85e59a-ed4a-4516-b2ef-67e213cfa2a1
  cTime=0
  datanodeUuid=54bc8b80-b84f-4893-8b96-36568acc5d4b
  storageType=DATA_NODE
  layoutVersion=-56
  </code></pre>
  
  <p><strong>THE DataNode</strong></p>
  
  <pre><code>storageID=DS-f72f5710-a869-489d-9f52-40dadc659937
  clusterID=CID-cd85e59a-ed4a-4516-b2ef-67e213cfa2a1
  cTime=0
  datanodeUuid=54bc8b80-b84f-4893-8b96-36568acc5d4b
  storageType=DATA_NODE
  layoutVersion=-56
  </code></pre>