Installing Java for Hadoop

Java is the main prerequisite for Hadoop. First of all, you should verify the existence of java in your system using the command “java -version”. The syntax of java version command is given below.

$ java -version 

If everything is in order, it will give you the following output.

java version "1.7.0_71" 
Java(TM) SE Runtime Environment (build 1.7.0_71-b13) 
Java HotSpot(TM) Client VM (build 25.0-b02, mixed mode)  

If java is not installed in your system, then follow the steps given below for installing java.

Step 1

Download java (JDK <latest version> - X64.tar.gz) by visiting the following link http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads1880260.html.
Then jdk-7u71-linux-x64.tar.gz will be downloaded into your system.

Step 2

Generally you will find the downloaded java file in Downloads folder. Verify it and extract the jdk-7u71-linux-x64.gz file using the following commands.

$ cd Downloads/ 
$ ls 
jdk-7u71-linux-x64.gz 
$ tar zxf jdk-7u71-linux-x64.gz 
$ ls 
jdk1.7.0_71   jdk-7u71-linux-x64.gz 

Step 3

To make java available to all the users, you have to move it to the location “/usr/local/”. Open root, and type the following commands.

$ su 
password: 
# mv jdk1.7.0_71 /usr/local/ 
# exit 

Step 4

For setting up PATH and JAVA_HOME variables, add the following commands to ~/.bashrc file.

export JAVA_HOME=/usr/local/jdk1.7.0_71 
export PATH=$PATH:$JAVA_HOME/bin 

Now apply all the changes into the current running system.

$ source ~/.bashrc

Step 5

Use the following commands to configure java alternatives:

# alternatives --install /usr/bin/java java usr/local/java/bin/java 2

# alternatives --install /usr/bin/javac javac usr/local/java/bin/javac 2

# alternatives --install /usr/bin/jar jar usr/local/java/bin/jar 2

# alternatives --set java usr/local/java/bin/java

# alternatives --set javac usr/local/java/bin/javac

# alternatives --set jar usr/local/java/bin/jar

Now verify the java -version command from the terminal as explained above.