How to determine JAVA_HOME on Debian/Ubuntu?

Question

On Ubuntu it is possible to have multiple JVMs at the same time. The default one is selected with update-alternatives. But this does not set the JAVA_HOME environment variable, due to a debian policy.

I am writing a launcher script (bash), which starts a java application. This java application needs the JAVA_HOME environment variable. So how to get the path of the JVM which is currently selected by update-alternatives?

Answer 1

Something like this should do the trick:

JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")

Answer 2

So, you're saying that this command does nothing for you?

sudo update-alternatives --config java 

Answer 3

danadam's solution can easily be adopted to retrieve the JDK (i.e. not JRE) path as required:

JAVA_HOME=$(readlink -f /usr/bin/javac | sed "s:/bin/javac::")

• Looks for javac Java compiler (instead of java) included in JDK (but not JRE).
• Has no trailing / (stripped off by sed s:/bin... instead of s:bin...)

Answer 4

A while ago I created a tutorial on the Ubuntu forum on how to install the latest JRE/JDK from the Java website. It also covers on how to enable it system-wide, by adding the JRE/JDK location to the PATH variable. If you like, you can also add JAVA_HOME to the script, mentioned at the end of the topic.

Check it out: http://ubuntuforums.org/showthread.php?t=1437100

Answer 5

As an extension of danadams answer:

First of all, install the 2nd Java JRE as the 3rd java option, with priority of "3":

sudo alternatives --install /usr/lib/jvm/jre jre /opt/IBM/java/jre/bin/java 3

Then, you can list them:

update-alternatives --list java

You can set the alternative by hand , using this:

sudo alternatives --config java /opt/IBM/java/jre/bin/java

Then, your script can set it on the fly, like so:

sudo alternatives --set java /opt/IBM/java/jre/bin/java
JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")

This better illustrates what the 'sed' command is doing.

Answer 6

export JAVA_HOME=$(dirname $(dirname $(readlink -f /usr/bin/java)))

In .bashrc was handy for me.