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Witek
Asked: 2010-05-21 07:09:42 +0800 CST

How to determine JAVA_HOME on Debian/Ubuntu?

  • 772

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?

java ubuntu debian

8 Answers

  1. Best Answer

    For the JRE, something like this should do the trick:

    JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")
    • 148

  2. 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...)
    • 51

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

    In .bashrc was handy for me.

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

    sudo update-alternatives --config java
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  5. I installed java with

    sudo apt-get install openjdk-7-jre-headless

    and then to find the location

    ls -al /etc/alternatives/java
    • 3

  6. 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. Although you still need to set the links for javaw and javac, etc, as well, each done separately.

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  7. 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

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  8. If java is configured with update-alternatives or was added to your PATH variable manually, then no hardcoded "/usr/bin/java" is needed. I use this solution in my .bashrc:

    export JAVA_HOME=$(readlink -m $(which java)/../..)

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