Install Java

Applies to Debian 12/13, Ubuntu 22.04/24.04, AlmaLinux 9 and Rocky Linux 9. We install Eclipse Temurin, the free Java builds from Adoptium, from their official package repository. Updates then come through apt or dnf like any other package.

The commands run as root. With a sudo user, put sudo in front.

Which version do you need?

Paper and many modpacks state the minimum version on their site. You can install several versions side by side.

For servers, the JRE is enough (temurin-21-jre). If you want to compile Java code on the server, take the JDK (temurin-21-jdk).

Debian and Ubuntu

Set up the repository

apt install -y wget gpg ca-certificates
install -d -m 0755 /etc/apt/keyrings
wget -qO - https://packages.adoptium.net/artifactory/api/gpg/key/public | gpg --dearmor -o /etc/apt/keyrings/adoptium.gpg
echo "deb [signed-by=/etc/apt/keyrings/adoptium.gpg] https://packages.adoptium.net/artifactory/deb $(. /etc/os-release && echo "$VERSION_CODENAME") main" > /etc/apt/sources.list.d/adoptium.list
apt update

$VERSION_CODENAME is the name of your release (bookworm, trixie, jammy, noble); the command fills it in for you.

Install Java

apt install -y temurin-21-jre

Other versions the same way:

apt install -y temurin-25-jre temurin-17-jre temurin-8-jre

To see what's available:

apt search temurin

AlmaLinux and Rocky Linux

Set up the repository

cat > /etc/yum.repos.d/adoptium.repo <<'EOF'
[Adoptium]
name=Adoptium
baseurl=https://packages.adoptium.net/artifactory/rpm/rhel/9/$basearch
enabled=1
gpgcheck=1
gpgkey=https://packages.adoptium.net/artifactory/api/gpg/key/public
EOF

Install Java

dnf install -y temurin-21-jre

The first time, dnf asks whether to import the Adoptium key; -y answers yes. More versions:

dnf install -y temurin-25-jre temurin-17-jre temurin-8-jre

Check that it worked

java -version

The output looks roughly like this:

openjdk version "21.0.9" 2025-10-21 LTS
OpenJDK Runtime Environment Temurin-21.0.9+10 (build 21.0.9+10-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.9+10 (build 21.0.9+10-LTS, mixed mode, sharing)

What matters is the first number and the word Temurin. Your exact update version will be newer.

Switch between versions

With several versions installed, one of them is the default for the java command.

Debian and Ubuntu:

update-alternatives --config java

AlmaLinux and Rocky Linux:

alternatives --config java

You get a numbered list; type the number you want and press Enter. Afterwards java -version shows the new version.

Call a specific version directly

For a server that always needs the same version, the full path is safer than the default. Find the paths with:

ls /usr/lib/jvm/

A start with a fixed version then looks something like:

/usr/lib/jvm/temurin-17-jre-amd64/bin/java -jar server.jar

The folder name differs between Debian/Ubuntu and AlmaLinux/Rocky; use the one ls shows.

Updates

Java updates arrive with the normal system update:

apt update && apt upgrade        # Debian and Ubuntu
dnf upgrade                      # AlmaLinux and Rocky Linux

Running Java programs only use the new version after they are restarted.

Common errors

What next

• Minecraft server with Paper.
• Add swap if Java wants more RAM than is free.
• Help: ticket.