echo $JAVA_HOME returns nothing

Question

How to get the java home dir?

When doing this

echo $JAVA_HOME

Nothing is returned

Answer 1

You need to set the $JAVA_HOME variable

In my case while setting up Maven, I had to set it up to where JDK is installed.

First find out where JAVA is installed:

$ whereis java
java: /usr/bin/java /usr/share/java /usr/share/man/man1/java.1.gz

Now dig deeper-

$ ls -l /usr/bin/java
lrwxrwxrwx 1 root root 46 Aug 25  2016 /etc/alternatives/java -> /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

Dig deeper:

$ ls -l /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
-rwxr-xr-x 1 root root 6464 Mar 14 18:28 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

As it is not being referenced to any other directory, we'll use this.

Open /etc/environment using nano

$ sudo nano /etc/environment

Append the following lines

JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-amd64
export JAVA_HOME

Reload PATH using $ . /etc/environment

Now, $ echo $JAVA_HOME

Here is your output:

/usr/lib/jvm/java-1.8.0-openjdk-amd64

Sources I referred to:

https://askubuntu.com/a/175519

https://stackoverflow.com/a/23427862/6297483

Answer 2

$JAVA_HOME is a global variable that you typically must set yourself.

In certain (most?) platforms, installing Java will not set your JAVA_HOME variable.

The advantage here is that you can have multiple Java versions co-existing within one system.

Since you're running on *nix system, you can do that in your own logon scripts, such as ~/.bashrc or ~/.bash_profile, etc.