1. Hadoop install web site: http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/SingleCluster.html

Follow the steps and it gets work. But for the Pseudo-Distributed mode, need following point 4.

2. Hadoop download web site: http://www.apache.org/dyn/closer.cgi/hadoop/common/

3. Java install: sudo apt-get install oracle-java8-installer

Java 1.8 supports Hadoop 3.0.0 alpha1 (both run and build)

update Java alternatives:

sudo update-alternatives --config java

sudo update-alternatives --config javac

4. configure ssh to pdsh default connection ( or can't start namenode and datanode, it will report connection issue).

create file rcmd_default at /etc/pdsh

5. Hadoop example build web site: http://hadoop.apache.org/docs/current/hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduceTutorial.html

Follow the steps to build the code. JAVA 1.8 is good. OPENJDK 1.7 reports build warning and can't run the hadoop example.

6. run the built example, need add the package name of the class. Or the java will report can't find the class.