How to install Java on Windows and Ubuntu: OpenJDK 21 and 25, JAVA_HOME

Short answer: on Windows or Windows Server, install Eclipse Temurin, a free OpenJDK build: the MSI from adoptium.net, or winget install --id EclipseAdoptium.Temurin.25.JDK -e. On Ubuntu or Debian, run sudo apt install default-jdk, or name a version such as openjdk-21-jdk. Check with java -version. For anything new, pick an LTS release: Java 25 or 21.

sudo apt update
sudo apt install -y openjdk-21-jdk          # or openjdk-25-jdk, or default-jdk
java -version

winget install --id EclipseAdoptium.Temurin.25.JDK -e
# open a new window, then:
java -version

Nothing here was run for this page: it is written on a Debian host without Java. The package versions come from the Ubuntu archive on Launchpad and from packages.debian.org, the Windows details from Adoptium’s installation pages and the winget-pkgs manifests, and the release dates from openjdk.org, all read on 21 October 2026.

Which Java version should I install?

Java ships a feature release every six months, and every two years one of them is a long-term support (LTS) release that gets years of updates. Install an LTS unless a program asks for something else:

The next LTS is planned as Java 29 in September 2027, per Oracle’s roadmap. Two more choices come with every version:

• JDK or JRE. The JRE runs Java programs. The JDK adds the compiler javac and the developer tools. Developers and build servers need the JDK; a program that only runs, such as a Minecraft server, needs the JRE.
• Headless. On Linux, -headless packages leave out the graphical libraries. That is what a server wants: fewer packages, nothing that needs a display.

OpenJDK or Oracle JDK?

OpenJDK builds (your distribution’s openjdk packages, Eclipse Temurin, the Microsoft Build of OpenJDK) are licensed under the GPL version 2 with the Classpath Exception: free for any use, including production. Oracle JDK is Oracle’s own build under Oracle’s terms. As of October 2026, per Oracle’s licensing FAQ and Java blog, Oracle JDK 25 is under the Oracle No-Fee Terms and Conditions, free in production too, with free updates planned until September 2028. Oracle JDK 21 updates from the October 2026 Critical Patch Update onward are under the OTN licence, which is free for personal and development use but needs a paid subscription in production. Unless you want Oracle’s support contract, an OpenJDK build saves you the licence question entirely.

How do I install Java on Ubuntu and Debian?

Every Ubuntu and Debian release has a default-jdk package (and default-jre, default-jre-headless) that points at the version the release considers standard, plus versioned packages next to it:

sudo apt update

# a developer machine or build server: the JDK
sudo apt install -y openjdk-21-jdk

# a server that only runs a Java program: the headless runtime
sudo apt install -y openjdk-21-jre-headless

java -version
javac -version          # only with a JDK

Prefer a versioned package over default-jdk on a server. The default moves when you upgrade the release (Ubuntu 22.04 to 24.04 takes it from 11 to 21), and a program that was happy on one version can refuse the next. java -version prints three lines: the version (openjdk version "21.0.x"), the build of the runtime and the VM. If it prints a version you did not expect, another Java is still the default; see several versions below.

Eclipse Temurin from Adoptium’s repository

Debian 12 packages only Java 17, and some people want the same build on every distribution. Adoptium, the Eclipse project behind Temurin, runs its own apt repository with every LTS version. Its packages are named temurin-VERSION-jdk and temurin-VERSION-jre:

sudo apt install -y curl ca-certificates gpg
sudo install -d -m 0755 /etc/apt/keyrings
curl -fsSL https://packages.adoptium.net/artifactory/api/gpg/key/public \
  | sudo 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" \
  | sudo tee /etc/apt/sources.list.d/adoptium.list
sudo apt update
sudo apt install -y temurin-25-jdk

Adoptium’s own instructions put the key in /etc/apt/trusted.gpg.d/; the version above binds it to this one repository with signed-by, which is the safer modern form. If apt update then complains about a missing key, the NO_PUBKEY guide walks through it. On Rocky Linux and AlmaLinux, the distribution packages are called java-21-openjdk-headless (runtime) and java-21-openjdk-devel (JDK); dnf list --available 'java-*-openjdk-headless' shows which versions your point release has.

Several Java versions: update-alternatives

Java versions install side by side under /usr/lib/jvm, and /usr/bin/java is a link managed by the alternatives system. Pick the default like this:

ls /usr/lib/jvm                              # what is installed
sudo update-alternatives --config java        # choose the default java
sudo update-alternatives --config javac       # and the compiler, separately

--config lists every installed java with a number and marks the current one with *; type a number, or press Enter to keep it. java and javac are separate entries, so after switching one, switch the other too, or javac compiles for a different version than java runs. For a service that must stay on one version whatever the default is, skip the alternatives and call the binary by its full path, such as /usr/lib/jvm/java-21-openjdk-amd64/bin/java. Rocky Linux and AlmaLinux use the same mechanism under the name alternatives.

How do I set JAVA_HOME on Linux?

Build tools such as Maven and Gradle, and some application servers, look for JAVA_HOME. It must name the JDK’s root directory, the one that contains bin, not the java binary itself:

readlink -f "$(command -v java)"
# /usr/lib/jvm/java-21-openjdk-amd64/bin/java   ->  JAVA_HOME is the part before /bin/java

# for every user, at the next login
echo 'export JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64' | sudo tee /etc/profile.d/java-home.sh

# or follow whatever update-alternatives selects
export JAVA_HOME="$(dirname "$(dirname "$(readlink -f "$(command -v java)")")")"

Temurin installs to /usr/lib/jvm/temurin-25-jdk-amd64 and similar. A variable set in a profile file reaches login shells only, not systemd services or cron jobs; setting environment variables on Linux covers Environment= for services and the other places it can live.

How do I install Java on Windows and Windows Server?

The same Temurin builds exist for Windows as MSI installers, and they work on Windows 10 and 11 as well as on Windows Server. Two ways to install them:

1. 1Download the MSI from adoptium.net

   Pick the version (25 or 21), the operating system Windows, the architecture x64 and the package type JDK or JRE, and download the .msi.

2. 2Turn on the JAVA_HOME feature during setup

   The installer updates PATH by default, but “Set JAVA_HOME variable” is off unless you select it on the custom setup page. For an unattended install, list the features yourself:

   msiexec /i TEMURIN-JDK.msi ADDLOCAL=FeatureMain,FeatureEnvironment,FeatureJarFileRunWith,FeatureJavaHome /quiet

   Replace TEMURIN-JDK.msi with the file you downloaded. FeatureJavaHome sets JAVA_HOME, FeatureEnvironment adds Java to PATH.

3. 3Check it in a new window

   java -version
   where.exe java
   echo $env:JAVA_HOME          # PowerShell; in cmd: echo %JAVA_HOME%

With winget it is one line: winget install --id EclipseAdoptium.Temurin.25.JDK -e, or EclipseAdoptium.Temurin.21.JDK, and .JRE instead of .JDK for the runtime only; winget search Temurin lists them all. The winget manifest installs the MSI machine-wide with all features, so JAVA_HOME is set too. winget is built into Windows 10, 11 and Server 2025 but not supported on Server 2022 and 2019; winget on Windows Server covers getting it there, or use the MSI.

To set JAVA_HOME by hand, for example after a zip install, use System Properties, Environment Variables, or PowerShell as Administrator. The default Temurin folder is C:\Program Files\Eclipse Adoptium\jdk-VERSION-hotspot:

Get-ChildItem 'C:\Program Files\Eclipse Adoptium'          # find the exact folder name
[Environment]::SetEnvironmentVariable('JAVA_HOME', 'C:\Program Files\Eclipse Adoptium\jdk-25.0.4.7-hotspot', 'Machine')

Which Java does a Minecraft server need?

The server is where Java has to be installed by hand, and the version must be at least what the game version requires. Mojang’s changelog for 26.1 (released 24 March 2026) moved the requirement to Java 25; the Minecraft Wiki’s server tutorial lists the earlier steps:

A newer Java usually runs an older game version (1.16 runs on Java 17, per the same tutorial), but mod loaders for old versions can be stricter than the game, so follow the loader’s notes there. The complete server setup, with RAM sizing, a systemd service and the firewall, is in making a Minecraft server on a VPS; Forge, NeoForge and Fabric packs are covered in the modded Minecraft server guide.

Common Java install errors

Java on a VPS or dedicated server

On a server, install the headless JRE of the exact version the program needs, pin it with the full path in the service file, and size the heap with -Xmx below the machine’s RAM so the operating system keeps room. If the whole process grows past the RAM anyway, the kernel ends it without a Java error in the log; the OOM killer guide shows how to confirm that.

A Linux VPS with Ubuntu 24.04 or Debian 13 from the template has Java 21 and 25 one apt install away. For Java software that only runs on Windows, a Windows VPS with Windows Server 2022 or 2019 takes the Temurin MSI the same way a desktop does.

Frequently asked