Ubuntu – How to determine JAVA_HOME on Debian/Ubuntu

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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?

Best Answer

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

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

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Ideally you need to set two environment variables:

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You can either create different scripts to start the various programs and set these variables differently in each case. Or you can configure each application to start under a different user account and set these variables in the users appropriate startup script.

$JAVA_HOME/bin needs to come first on the PATH to avoid any other java binaries on the default path being run instead.

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At least on Ubuntu 10.04, /etc/init.d/tomcat6 sources /etc/default/tomcat6 if it exists. That's where I put my overrides, and I believe it's generally the "approved" way to make such changes.

Best Answer

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