Hadoop - namenode is not starting up

DFS needs to be formatted. Just issue the following command after stopping all and then restart.

hadoop namenode -format

Cool, i have found the solution.

Stop all running server

1) stop-all.sh 

Edit the file /usr/local/hadoop/conf/hdfs-site.xml and add below configuration if its missing

<property>
    <name>dfs.data.dir</name>
    <value>/app/hadoop/tmp/dfs/name/data</value> 
    <final>true</final> 
    </property> 
    <property> 
    <name>dfs.name.dir</name>
    <value>/app/hadoop/tmp/dfs/name</value> 
    <final>true</final> 
</property>

Start both HDFS and MapReduce Daemons

2) start-dfs.sh
3) start-mapred.sh

Then now run the rest of the steps to run the map reduce sample given in this link

Note : You should be running the command bin/start-all.sh if the direct command is not running.