CODEWITHSUNDEEP
javaubuntupath
user204069
user204069

Reputation: 1091

Even if $JRE_HOME is not set java -version is displaying properly

I used sudo apt-get open-jdk7 to install Java on my Ubuntu OS.

When I open a terminal and type echo $JRE_HOME it displays nothing. But then I do java -version it shows me correct version of OpenJDK. Also when I simply type java it works.

Not sure how Ubuntu set the path of java.

Similarly javac works but I don't see anything when I say echo $JAVA_HOME.

My path does not show java directory path in it.

Where is Ubuntu setting the java path? Why does Ubuntu not set JAVA_HOME and JRE_HOME during installation of OpenJDK?

Upvotes: 1

Views: 5039

Answers (3)

Joachim Sauer
Joachim Sauer

Reputation: 308249

It's a common misconception that Java somehow requires JAVA_HOME, JRE_HOME or similar environment variables to be set to work.

In fact the java and javac (and related) executables don't really care about those variables. They only need to be on the PATH (or can be executed via a full path if not on PATH) and will find their related install by looking "near itself" (i.e. the executable are usually installed in a known location relative to the JVM files).

There are a few third party scripts that use JAVA_HOME and/or JRE_HOME to find a Java installation (Apache Tomcat is a well-known example for this), but the Java executables themselves don't need those variables.

As to how Ubuntu finds the executables is easy to answer: use which java and which javac to find out which executables are executed when you type those commands. On Debian-based systems they are usually a series of symlinks through the alternatives systems that point to the actual executables.

Upvotes: 5

Tamas Rev
Tamas Rev

Reputation: 7174

As many Linux distros, Ubuntu has /etc/alternatives in its paths. If you type:

which java

Then you'll get

/etc/alternatives/java

If you type:

ls -l /etc/alternatives/java

Then you'll get

/etc/alternatives/java -> /usr/lib/jvm/<your java version>

A few mor ls -l -s can help you to get the full picture.

Upvotes: 1

Grim
Grim

Reputation: 2040

"Where is ubuntu setting java path?", ubuntu does not set the open-jdk-java-path automatically. try 

find / -name "java"

to locate the javac. And write

export JRE_HOME="xxx"

(where xxx is the base of the open-jdk-jre.)

BTW: You got nothing than trouble with open-jdk. You better use the sun-jdk.

Upvotes: 1

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