title: hadoop : datanode not running?
body: <p>I configured and deployed hadoop for single node setup via<a href="http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/" rel="nofollow"> this </a> tutorial. Everything deployed fine, but when I do jps for have a look on active processes, datanode is not shown. I manually tried to start datanode by going to $HADOOP_HOME/bin : hadoop -datanode, but to no avail. Basically to sum up, datanode process is not running at all for the hadoop cluster. Also, I want to know whether a single machine can have 2 hadoop installations. I am using one for mapreduce processes and another one for search engine. So their directory being different, is that okay ? Also, I run a single hadoop operation at a time.</p>
  
  <p><strong>EDIT</strong> 1#:- if this helps, here's the log when I tried running datanode via $HADOOP_HOME.</p>
  
  <pre><code>root@thinktank:/usr/local/hadoop/bin# hadoop datanode Warning: $HADOOP_HOME is deprecated.
  
  13/08/27 16:34:57 INFO datanode.DataNode: STARTUP_MSG: /********************************** STARTUP_MSG: Starting DataNode STARTUP_MSG: host = thinktank/127.0.1.1 STARTUP_MSG: args = [] STARTUP_MSG: version = 1.2.1 STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2 -r 1503152; compiled by 'mattf' on Mon Jul 22 15:23:09 PDT 2013
  STARTUP_MSG: java = 1.6.0_27
  **********************************/
  13/08/27 16:34:57 INFO impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
  13/08/27 16:34:57 INFO impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered.
  13/08/27 16:34:57 INFO impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
  13/08/27 16:34:57 INFO impl.MetricsSystemImpl: DataNode metrics system started
  13/08/27 16:34:57 INFO impl.MetricsSourceAdapter: MBean for source ugi registered.
  13/08/27 16:34:57 WARN impl.MetricsSystemImpl: Source name ugi already exists!
  13/08/27 16:34:57 ERROR datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in /app/hadoop/tmp/dfs/data: namenode namespaceID = 1955988395; datanode namespaceID = 1705269445 at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:232) at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:147) at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:414) at org.apache.hadoop.hdfs.server.datanode.DataNode.(DataNode.java:321) at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1712) at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1651) at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1669) at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:1795) at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1812)
  
  13/08/27 16:34:57 INFO datanode.DataNode: SHUTDOWN_MSG: /********************************** SHUTDOWN_MSG: Shutting down DataNode at thinktank/127.0.1.1 **********************************/
  </code></pre>