Upgrade Hadoop Namenode from hadoop 2.3.0 to 2.6.0

If you are about to upgrade hadoop from hadoop 2.3.0 to 2.6.0, then you can make use of existing namenode image just by upgrading namenode with below command. This is one time

$> hadooop namenode start -upgrade

This upgrades the old namenode meta data to newer format.

After this to finalize the upgrade execute below command

$> hdfs dfsadmin -finalizeUpgrade