# Java Upgrade 21.x (Ubuntu) This article provides step-by-step instructions to upgrade Java from JDK 17 to JDK 21 on an Ubuntu machine. It includes procedures for stopping Apache Tomcat services, installing Java 21, updating the default Java version, and restoring SSL certificates from the existing Java installation. The article also covers verification steps to ensure the upgraded Java version integrates successfully with Apache Tomcat services. This upgrade helps maintain compatibility, security, and performance for OvalEdge deployments and related services. ## Prerequisites Complete the following prerequisites before starting the upgrade: * Ensure sudo or root access is available on the Ubuntu machine. * Back up the existing Java options and heap settings configured for Apache Tomcat services. * Stop all Tomcat services before starting the upgrade. * Ensure internet access is available to download the required JDK packages. * Verify sufficient disk space is available for installation. * Validate Java 17 and Java 21 compatibility requirements for Elasticsearch 9.x before starting the upgrade. ## Stop Apache Tomcat Services 1. Stop all running Tomcat services before upgrading Java. 2. Run the following command to stop the default Tomcat service: ``` sudo systemctl stop tomcat.service ``` 3. If multiple Tomcat instances are running, stop each instance separately: ``` sudo systemctl stop tomcat-ui sudo systemctl stop tomcat-job ``` 4. Verify the Tomcat service status: ``` sudo systemctl status tomcat ``` ## Verify Current Java Version 1. Verify the currently installed Java version before starting the upgrade. 2. Run the following command: ``` java -version ``` 3. Expected output: ``` openjdk version "17.x.x" ``` Sample Reference Screenshot:
## Back Up Existing cacerts File Back up the existing cacerts file to preserve custom SSL certificates. 1. Run the following command to create a backup directory: ``` mkdir -p /home/ubuntu/cacertsbackup ``` 2. Navigate to the existing Java security directory and run the following command: ``` cd /usr/lib/jvm/java-17-openjdk-amd64/lib/security ``` 3. Run the following command to back up the cacerts file: ``` cp cacerts /home/ubuntu/cacertsbackup/ ``` Sample Reference Screenshot:
4. To verify backup, run the following command: ``` ls -l /home/ubuntu/cacertsbackup ``` Sample Reference Screenshot:
## Update System Packages 1. Update the Ubuntu package repository and installed packages. 2. Run the following commands: ``` sudo apt update sudo apt upgrade -y ``` ## Install Java 21 1. Install OpenJDK 21 using the Ubuntu package repository. 2. Run the following command: ``` sudo apt install openjdk-21-jdk -y ``` Sample Reference Screenshot:
3. Verify the installation: ``` java -version ``` Sample Reference Screenshot:
### Verify Installed Java Versions 1. Verify all installed Java versions on the machine. 2. Run the following command: ``` sudo update-alternatives --list java ``` Sample Reference Screenshot:
3. Expected output: ``` /usr/lib/jvm/java-17-openjdk-amd64/bin/java /usr/lib/jvm/java-21-openjdk-amd64/bin/java ``` ## Set Java 21 as the Default Version 1. Configure Java 21 as the default Java version. 2. Run the following command: ``` sudo update-alternatives --config java ``` 3. Select the option corresponding to Java 21 from the displayed list.\ Sample Reference Screenshot:
## Verify Java Upgrade 1. Verify that the system is using Java 21 as the active Java version. 2. Run the following command: ``` java -version ``` 3. Expected output: ``` openjdk version "21.0.10" 2026-01-20 OpenJDK Runtime Environment (build 21.0.10+7-Ubuntu-122.04) OpenJDK 64-Bit Server VM (build 21.0.10+7-Ubuntu-122.04, mixed mode, sharing) ``` ## Restore cacerts File Restore the previously backed-up cacerts file into the Java 21 security directory. ### Copy Backup cacerts File 1. Run the following command: ``` sudo cp /home/ubuntu/cacertsbackup/cacerts /usr/lib/jvm/java-21-openjdk-amd64/lib/security/ ``` ### Update File Permissions 1. Set the required permissions for the restored file: ``` sudo chmod 644 /usr/lib/jvm/java-21-openjdk-amd64/lib/security/cacerts ``` ### Update File Ownership 1. Set the correct ownership for the restored file: ``` sudo chown root:root /usr/lib/jvm/java-21-openjdk-amd64/lib/security/cacerts ``` ### Verify Restored File 1. Run the following command: ``` ls -l /usr/lib/jvm/java-21-openjdk-amd64/lib/security/cacerts ``` 2. Expected output: ``` -rw-r--r-- 1 root root cacerts ``` ## Start Apache Tomcat Services 1. Restart Apache Tomcat services after completing the Java upgrade. 2. Run the following command: ``` sudo systemctl start tomcat ``` 3. Verify the Tomcat service status: ``` sudo systemctl status tomcat ``` 4. If multiple Tomcat instances are configured, start each service separately: ``` sudo systemctl start tomcat-ui sudo systemctl start tomcat-job ``` *** Copyright © 2026, OvalEdge LLC, Peachtree Corners, GA, USA. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ovaledge.com/release8.1/deployment-and-maintenance/upgrade/java-upgrade-21.x-ubuntu.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.