Home How To Install Java 21 LTS (OpenJDK) on RHEL 10 / Rocky Linux 10...

Install Java 21 LTS (OpenJDK) on RHEL 10 / Rocky Linux 10 / AlmaLinux 10

March 18, 2026

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Java 21 is the latest long-term support (LTS) release from Oracle and the OpenJDK community, with support guaranteed until at least September 2029. If you are running production workloads on RHEL 10, Rocky Linux 10, or AlmaLinux 10, this is the version you should be deploying. It brings virtual threads, pattern matching improvements, and a range of performance gains over Java 17 and earlier releases.

In this guide, I will walk you through two methods to install OpenJDK 21 on RHEL 10-based distributions – using the default AppStream repository and using the Eclipse Temurin (Adoptium) repository. We will also cover setting JAVA_HOME properly, managing multiple Java versions with the alternatives system, and configuring Java for build tools and application servers.

Prerequisites

Before you begin, make sure you have the following in place:

A running installation of RHEL 10, Rocky Linux 10, or AlmaLinux 10
Root or sudo access to the server
An active internet connection for package downloads
The system should be up to date – run sudo dnf update -y before proceeding

JDK vs JRE – Which One Do You Need?

Before installing, understand the difference between the two main packages:

JRE (Java Runtime Environment) – contains only the runtime needed to execute Java applications. Install this on servers that only run pre-compiled Java apps like Tomcat, Elasticsearch, or Kafka.
JDK (Java Development Kit) – includes the JRE plus development tools like javac (compiler), jdb (debugger), and jar (archive tool). Install this if you need to compile Java code, run Maven or Gradle builds, or do any development work.

My recommendation: install the full JDK unless you are absolutely certain you only need the runtime. The extra disk space is minimal and it saves you from headaches later when a tool expects javac to be present.

Method 1 – Install OpenJDK 21 from AppStream Repository

RHEL 10 and its derivatives ship OpenJDK 21 in the AppStream repository. This is the simplest and most straightforward installation method, and the packages receive security updates through your normal system update process.

Step 1 – Install OpenJDK 21 JDK

To install the full JDK (recommended):

sudo dnf install -y java-21-openjdk-devel

If you only need the JRE:

sudo dnf install -y java-21-openjdk

Step 2 – Verify the Installation

Check the Java runtime version:

java -version

Expected output:

openjdk version "21.0.6" 2025-01-21 LTS
OpenJDK Runtime Environment (Red_Hat-21.0.6.0.7-1) (build 21.0.6+7-LTS)
OpenJDK 64-Bit Server VM (Red_Hat-21.0.6.0.7-1) (build 21.0.6+7-LTS, mixed mode, sharing)

If you installed the JDK, also verify the compiler:

javac -version

Expected output:

javac 21.0.6

Method 2 – Install Eclipse Temurin (Adoptium) from Official Repository

Eclipse Temurin is a production-ready OpenJDK distribution maintained by the Adoptium project. It is a solid alternative if you want builds that are independent of your OS vendor’s release cycle, or if your organization standardizes on Temurin across different platforms.

Step 1 – Add the Adoptium Repository

First, create the repository configuration file:

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

Step 2 – Install Temurin 21 JDK

Install the package:

sudo dnf install -y temurin-21-jdk

Step 3 – Verify the Installation

Check the installed version:

java -version

You should see output similar to:

openjdk version "21.0.6" 2025-01-21 LTS
OpenJDK Runtime Environment Temurin-21.0.6+7 (build 21.0.6+7-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.6+7 (build 21.0.6+7-LTS, mixed mode, sharing)

Set JAVA_HOME System-Wide

Many Java applications, build tools, and frameworks expect the JAVA_HOME environment variable to be set. The cleanest way to do this system-wide on RHEL-based systems is to create a script in /etc/profile.d/.

Step 1 – Find Your Java Installation Path

Run the following to find where Java is installed:

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

For the AppStream OpenJDK package, this will typically return something like:

/usr/lib/jvm/java-21-openjdk-21.0.6.0.7-1.el10.x86_64

Step 2 – Create the JAVA_HOME Profile Script

Create /etc/profile.d/java.sh with the following content:

cat << 'EOF' | sudo tee /etc/profile.d/java.sh
export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java))))
export PATH=$JAVA_HOME/bin:$PATH
EOF

Make it executable:

sudo chmod +x /etc/profile.d/java.sh

Step 3 – Load and Verify

Source the script to apply it to your current session:

source /etc/profile.d/java.sh

Verify JAVA_HOME is set correctly:

echo $JAVA_HOME

This script will be loaded automatically for all users on their next login.

Manage Multiple Java Versions with Alternatives

If you have more than one Java version installed on the same system – for example, Java 17 for a legacy app and Java 21 for newer workloads – RHEL’s alternatives system lets you switch between them cleanly.

List Available Java Versions

See all installed Java runtimes registered with alternatives:

sudo alternatives --config java

This shows a numbered list of available versions. Enter the number corresponding to the version you want to use as the default, then press Enter.

Switch the Java Compiler

You should also switch the compiler to match:

sudo alternatives --config javac

Verify After Switching

Always verify after making a change:

java -version
javac -version

Both commands should now report the version you selected.

Configure Java for Common Applications

Apache Maven

Maven reads JAVA_HOME to locate the JDK. If you set it in /etc/profile.d/java.sh as described above, Maven will pick it up automatically. Install Maven with:

sudo dnf install -y maven

Verify it detects Java 21:

mvn -version

The output should show Java version: 21.x.x under the runtime information.

Gradle

Gradle also uses JAVA_HOME. If you are installing Gradle manually (not through dnf), download it from the official site and extract it:

wget https://services.gradle.org/distributions/gradle-8.12-bin.zip
sudo mkdir -p /opt/gradle
sudo unzip -d /opt/gradle gradle-8.12-bin.zip
export PATH=/opt/gradle/gradle-8.12/bin:$PATH

Verify:

gradle -version

Check that the JVM line shows Java 21.

Apache Tomcat

Tomcat 10.1.x and 11.x both support Java 21. If you install Tomcat from a tarball, set JAVA_HOME in the Tomcat service file or in /opt/tomcat/bin/setenv.sh:

cat << 'EOF' | sudo tee /opt/tomcat/bin/setenv.sh
export JAVA_HOME=$(dirname $(dirname $(readlink -f $(which java))))
EOF
sudo chmod +x /opt/tomcat/bin/setenv.sh

If you are using a systemd unit file for Tomcat, you can add the environment variable there instead:

[Service]
Environment="JAVA_HOME=/usr/lib/jvm/java-21-openjdk"

Then reload and restart:

sudo systemctl daemon-reload
sudo systemctl restart tomcat

Troubleshooting

java command not found after installation

If you get -bash: java: command not found right after installing, log out and log back in, or source the profile manually:

source /etc/profile.d/java.sh

If the file does not exist yet, check that the java binary is in the PATH:

which java
ls -la /usr/bin/java

Wrong Java version is active

If java -version shows an older version, another Java is taking priority. Check what alternatives are registered:

sudo alternatives --config java

Select the Java 21 entry. Also check if something in your shell profile is overriding the PATH:

which -a java

JAVA_HOME is not set or points to the wrong version

Verify the current value:

echo $JAVA_HOME

If it is empty or incorrect, re-create /etc/profile.d/java.sh as shown in the JAVA_HOME section above, then source it.

javac not found but java works

This means you installed the JRE (java-21-openjdk) but not the JDK. Install the development package:

sudo dnf install -y java-21-openjdk-devel

Then verify:

javac -version

Adoptium repository not working

If dnf fails to fetch packages from the Adoptium repo, check that the repo file is correct:

cat /etc/yum.repos.d/adoptium.repo

Make sure the baseurl contains $releasever (which resolves to 10 on RHEL 10). If Adoptium has not yet published packages for RHEL 10 specifically, you can try using the RHEL 9 path temporarily:

baseurl=https://packages.adoptium.net/artifactory/rpm/rhel/9/$basearch

Then clear the cache and retry:

sudo dnf clean all
sudo dnf install -y temurin-21-jdk

Permission denied errors

All installation commands require root or sudo. If you are running as a non-root user, prefix commands with sudo. If sudo is not configured for your user, ask your system administrator to add you to the wheel group:

sudo usermod -aG wheel yourusername

Summary

You now have Java 21 LTS installed and configured on your RHEL 10, Rocky Linux 10, or AlmaLinux 10 system. Whether you went with the AppStream OpenJDK package or Eclipse Temurin, the end result is a production-ready Java 21 environment. With JAVA_HOME set in /etc/profile.d/java.sh and the alternatives system configured, your Java setup will work correctly with Maven, Gradle, Tomcat, and any other Java-dependent tools you need to run.