Hadoop namenode not getting started

1. First delete all contents from temporary folder: rm -rf <tmp dir> (my was /usr/local/hadoop/tmp)
2. Format the namenode: bin/hadoop namenode -format
3. Start all processes again
   1. bin/start-dfs.sh
   2. bin/start-yarn.sh
   3. bin/mr-jobhistory-daemon.sh start historyserver

You may consider rolling back as well using checkpoint (if you had it enabled).