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Hadoop 1.0.4 on Ubuntu Linux 12.04 ( Single Node )- Part -3/3 Before starting the hadoop, you need to format the HDFS (i.e the hadoop filesystem) via the namenode. What this does is basically clears the directory values given in { dfs.name.dir}. This is the directory used by name-node to keep details of all the data in the data-node( i.e files), basically every detail required to track the which data sits in which data-node. Please understand that it does not store any data itself, it just stored the details of which data sits on which data-nodes. use the below command to format the name-node. ./hadoop-1.0.4/bin/hadoop namenode -format and the result looks like below. Now you can start your hadoop. ./hadoop-1.0.4/bin/start-all.sh and there result looks like this. Also check if all the required hadoop processes are running by typing jps.   If you face any problems then have a look into the logs file and investigate. and If you want to stop hadoop use teh below c