Step-1. Click on stop-all.sh and then click on start-all.sh OR
Step-2. Write sudo hdfs (press enter), su-hdfs (press enter), /etc/init.d/ha (press enter) and then /etc/init.d/hadoop-0.20-namenode start (press enter).
Which are the three modes in which Hadoop can be run?
The three modes in which Hadoop can be run are -
standalone (local) mode
Fully distributed mode
What does /etc /init.d do?
/etc /init.d specifies where daemons (services) are placed or to see the status of these daemons. It is very LINUX specific, and nothing to do with Hadoop.