Problem scenario
You have run start-dfs.sh and start-yarn.sh. You have stopped all the Hadoop services too. When you run "jps", the NameNode is not showing up. You have tried a variety of different troubleshooting methods (including rebooting the NameNode). The NameNode has never worked correctly. You can delete all the data in the cluster because it never really worked. What should you do?
Solution
Run this but remember it will delete all your data:
hdfs namenode -format # Warning: this command will delete all your data in Hadoop