Managing multiple Java versions on old Linux can be achieved using various methods, including manual installation and configuration with update-alternatives
Installation and Configuration:
Download and Extract:
Download the desired JDK/JRE binary from Oracle's website. Extract the archive to a specific directory (e.g., /opt/java/jdk17.0_version). Repeat for each Java version you want to install.
Set JAVA_HOME:
For a specific application or user, you can set the JAVA_HOME environment variable to point to the desired Java installation directory. This is typically done in the user's .bashrc or .profile file.
| # export
JAVA_HOME=/opt/java/jdk17.0_version # export PATH=$JAVA_HOME/bin:$PATH ## Repeat for other Java executables like 'jar', 'javadoc', etc. |
Update System-Wide Alternatives:
To make a specific Java version the default for all users, use the update-alternatives command.
| # update-alternatives --install
"/usr/bin/java" "java" "/opt/java/jdk17.0_version/bin/java" 1 # update-alternatives --install "/usr/bin/jar" "jar" "/opt/java/jdk17.0_version/bin/jar" 1 # update-alternatives --install "/usr/bin/javac" "javac" "/opt/java/jdk17.0_version/bin/javac" 1 # # Repeat for other Java executables like 'jar', 'javadoc', etc. |
The last argument 1 is the priority, which determines the default if multiple alternatives exist. Higher priority takes precedence.
Switching Versions:
To switch the default Java version system-wide, use:
| # update-alternatives --config java |
This will present a list of available Java installations, allowing you to choose the desired default by entering its corresponding number.
Important Notes:
- Be mindful of the licensing terms for Oracle JDK, as older versions might have different licensing models. OpenJDK is a free and open-source alternative.
- When using update-alternatives, ensure you add all relevant Java executables (e.g., java, javac, jar) to avoid inconsistencies.
- Test your Java applications after changing the default Java version to ensure compatibility.
