[How-To] Install OpenJDK 21 on Ubuntu 24 VM

Purpose

This article will focus on the installation of OpenJDK 21 on a headless Ubuntu 24 VM.

Prerequisites

List of prerequisites:

• Sudo user
• Ubuntu 24 LXC or VM

Instructions

Step 1: Install OpenJDK 21

First, update the system:

sudo apt update && sudo apt upgrade -y

Then, install OpenJDK 21:

sudo apt install openjdk-21-jdk -y

Step 2: Verify Installation

Finally, verify you have OpenJDK 21 installed by checking the version:

java -version

You should see output like this:

openjdk version "21" 2023-09-19
OpenJDK Runtime Environment (build 21+35-Ubuntu)
OpenJDK 64-Bit Server VM (build 21+35-Ubuntu, mixed mode)

Step 3: Set Default Version of Java (If Multiple Exist)

If you have installed more than one version of Java, you will want to select OpenJDK 21 as the default with this command and selecting the correct option for OpenJDK 21:

sudo update-alternatives --config java

Step 4: Set Java home (Optional)

To set Java_HOME, run:

echo 'export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java))))' >> ~/.bashrc
source ~/.bashrc

Verify with:

echo $JAVA_HOME

Now, OpenJDK 21 is installed and ready to use!