How to set JAVA environment variables in Linux or CentOS

How to set JAVA environment variables JAVA_HOME and PATH in Linux

After installing new java (jdk or jre) or latest Java you may have usually find that the version of java is not exactly the same which you have installed. It might be showing you the same old version.

How to check the java version which is currently set in linux system ?
Answer: Run the below given command

# java --version

or 

# java -version

Now we will install new Java and set the java variables

Download the rpm file from Oracle website. Click here (If you have installed with tar ball then again there is no problem)

I installed the jdk-1.7.0_21-fcs.i586 hence showing practical case to case (You can skip the step if you installed through tar ball)

Install JDK (java) rpm

rpm -ivh jdk-1.7.0_21-fcs.i586

Generally after installation Java file goes to the path /usr/java/jdk-xx-version/. In my case it is in

/usr/java/jdk1.7.0_21

To check where is the latest Java (JDK or JRE) you have installed in your system. Run below given command

find / -name java

How to set Java variable environment

Follow the given below steps (Replace the version no. as per your new Java version installed in your system)

Step1 : Open /root/.bash_profile through your text editor. (I prefer to use vi editor)
And paste the given below two lines

export JAVA_HOME=/usr/java/jdk1.7.0_21
export PATH=/usr/java/jdk1.7.0_21/bin:$PATH

Step 2 : Now enable the Java variable without system restart (On system restart it bydefault set the java variable)

 source /root/.bash_profile

Step 3: Now check the Java version,JAVA_HOME and PATH variables.It should show you correct information as you have set.

java --version

echo $JAVA_HOME

echo $PATH

Given below is the reference of my system’s root bash_profile file

[root@localhost ~]# cat /root/.bash_profile
# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin

export PATH

export JAVA_HOME=/usr/java/jdk1.7.0_21
export PATH=/usr/java/jdk1.7.0_21/bin:$PATH
[root@localhost ~]#

Other files and location where you can set Java variable and what are the difference

(1) /etc/profile = To set environment variable to all users

(2) $HOME/.bashrc = To set environment for login user.
(3) $HOME/.bash_profile = To set environment for login user

Note: .bash_profile is executed for login shells, while .bashrc is executed for interactive non-login shells.

(4) Create a shell script inside /etc/profile.d/ with .sh extension. and make the file executable.

(5) Create a shell script in some other location and give its path in /etc/rc.local

Referred ： http://sharadchhetri.com/2013/06/03/how-to-set-java-environment-variables-in-linux-or-centos/