How to Install Java (OpenJDK) on Ubuntu and Debian

Applies to: OpenJDK 17, 21 and 25 on Ubuntu 24.04 and Debian 13 (notes for AlmaLinux and Rocky Linux 9)

Ubuntu and Debian include OpenJDK, the free open-source Java. You need the JRE to run Java programs and the JDK to build them. We tested these steps on Ubuntu 24.04 and Debian 13.

Which version?

• 21: the default on Ubuntu 24.04 and Debian 13 (default-jdk), a long-term-support release.
• 25: the newest long-term-support release; needed for example by Minecraft 26.x.
• 17: for older applications that ask for it.

Check what your application needs before you choose.

Install

sudo apt update
sudo apt install default-jdk               # OpenJDK 21 (JDK)
sudo apt install openjdk-25-jdk            # or a specific version
sudo apt install openjdk-25-jre-headless   # just the runtime, for servers

-headless packages leave out the graphical parts, which a server doesn’t need.

Check it

java -version
javac -version       # only with a JDK

Several versions: choose the default

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

Pick the number of the version you want. More detail: how to work with multiple Java versions.

Set JAVA_HOME

Some tools need it. Find the folder of the active Java:

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

It prints something like /usr/lib/jvm/java-21-openjdk-amd64. Add it to /etc/environment as JAVA_HOME="/usr/lib/jvm/java-21-openjdk-amd64" and log in again.

Test with a small program

printf 'public class Hello { public static void main(String[] a) { System.out.println("Hello from Java " + System.getProperty("java.version")); } }\n' > Hello.java
java Hello.java

AlmaLinux and Rocky Linux

sudo dnf install java-21-openjdk-devel     # JDK (or java-25-openjdk-devel)
sudo dnf install java-25-openjdk-headless  # runtime only
sudo alternatives --config java

Running a Minecraft server? See how to make a Minecraft server on Linux.