Problem scenario: On Ubuntu, after installing Hadoop, when you enter the command '/usr/local/hadoop/bin/hadoop namenode -format' and you get this error:
"Error: JAVA_HOME is not set and could not be found."
Solution: Verify Java is installed ('java -version'). If it is not installed, you can use 'apt-get install -y default-jre'.
Next, go to hadoop-env.sh. Find the export JAVA_HOME stanza. Change the '${JAVA_HOME}' value to '/usr' with no quotes.
