Install JDK 21 on Linux

On <user_run_jdk>
wget https://github.com/adoptium/temurin21-binaries/releases/download/jdk-21.0.8%2B9/OpenJDK21U-jdk_x64_linux_hotspot_21.0.8_9.tar.gz

On root
update-alternatives --install /usr/bin/java java /home/<user_run_jdk>/jdk-21.0.8+9/bin/java 21
update-alternatives --install /usr/bin/javac javac /home/<user_run_jdk>/jdk-21.0.8+9/bin/javac 21