Find the Java SDK location on Linux

Finding the Java SDK location on Linux is a common task for developers who need to configure environment variables, set up IDEs, or manage multiple Java versions. This article demonstrates several reliable methods to locate your Java Development Kit (JDK) installation directory using built-in Linux commands.

Understanding Java Installations on Linux

On Linux systems, Java can be installed in various locations depending on the installation method and distribution. Common locations include /usr/lib/jvm/, /usr/java/, or /opt/java/. Additionally, many systems support multiple Java versions simultaneously, making it important to identify which version is currently active.

Method 1: Using update-java-alternatives

The update-java-alternatives command provides a comprehensive view of all installed Java versions. Use the -l (list) option to display all available alternatives:

update-java-alternatives -l

This command outputs information in the following format:

java-11-openjdk-amd64 1111 /usr/lib/jvm/java-11-openjdk-amd64
java-17-openjdk-amd64 1711 /usr/lib/jvm/java-17-openjdk-amd64

The output shows the alternative name, priority, and the full installation path for each Java version.

Method 2: Using update-alternatives

The update-alternatives command manages symbolic links for system commands. To find Java executable locations:

update-alternatives --list java
update-alternatives --list javac

Example output:

/usr/lib/jvm/java-11-openjdk-amd64/bin/java
/usr/lib/jvm/java-17-openjdk-amd64/bin/java

Method 3: Using which and readlink

Combine which and readlink commands to resolve symbolic links and find the actual Java installation:

readlink -f $(which java)
readlink -f $(which javac)

The -f option follows all symbolic links recursively, revealing the final destination:

/usr/lib/jvm/java-11-openjdk-amd64/bin/java
/usr/lib/jvm/java-11-openjdk-amd64/bin/javac

Method 4: Checking Environment Variables

If JAVA_HOME is already configured, you can check its value:

echo $JAVA_HOME

You can also use the java command itself to display system properties:

java -XshowSettings:properties -version 2>&1 | grep "java.home"

Managing Multiple Java Versions

When multiple Java versions are installed, you can switch between them using:

sudo update-alternatives --config java
sudo update-alternatives --config javac

This presents an interactive menu to select the default Java version.

Verification Commands

After locating your Java installation, verify the version and configuration:

java -version
javac -version

Conclusion

These methods provide reliable ways to locate Java SDK installations on Linux systems. The update-java-alternatives and readlink approaches are particularly useful for scripting and automation, while environment variable checking works well for quick verification of existing configurations.