How to Find the Jenkins Version in Linux

Finding the Jenkins version in Linux is crucial for several reasons, from troubleshooting issues and ensuring compatibility to planning upgrades and verifying security vulnerabilities. Here’s the most direct method: simply use the Jenkins CLI. Execute the command java -jar jenkins-cli.jar -s http://your_jenkins_url/ help (replacing http://your_jenkins_url/ with your actual Jenkins URL) from your Linux terminal. This command will output the Jenkins version at the top of the help information.

Multiple Avenues to Uncover Your Jenkins Version

While the Jenkins CLI command offers a quick solution, there are alternative methods that cater to different scenarios and preferences. These options provide flexibility and ensure you can always access the necessary information.

1. Examining the Jenkins Web Interface

The most straightforward approach, especially for those with GUI access, is to check the Jenkins web interface:

• Log into your Jenkins instance through your web browser.
• Navigate to the bottom right corner of any Jenkins page.
• The Jenkins version number is usually displayed in small text.

This method is quick and accessible, requiring no command-line expertise. It’s ideal for initial checks and for users who primarily interact with Jenkins through its web interface.

2. Utilizing the Jenkins REST API

For programmatic access or integration with other tools, the Jenkins REST API offers a powerful solution:

• Construct the appropriate API endpoint: http://your_jenkins_url/api/json (again, replace http://your_jenkins_url/ with your Jenkins URL).
• Use a tool like curl or wget to send a request to this endpoint.
• Parse the JSON response for the "jenkins" field, which contains the version number.

Example using curl:

curl -s http://your_jenkins_url/api/json | grep 'jenkins' 

This method is valuable for automation, scripting, and scenarios where you need to programmatically determine the Jenkins version.

3. Inspecting the Jenkins War File

If you have access to the Jenkins war file, you can extract the version information directly:

• Locate the jenkins.war file on your system. Its location depends on your installation method, but it often resides in directories like /var/lib/jenkins or /usr/share/jenkins.
• Unzip the war file.
• Look for the MANIFEST.MF file usually located inside the META-INF directory.
• Open MANIFEST.MF and search for the Jenkins-Version attribute.

Example using unzip:

unzip jenkins.war META-INF/MANIFEST.MF cat META-INF/MANIFEST.MF | grep "Jenkins-Version" 

This approach is helpful when you need to verify the version of a specific war file before deployment or after an upgrade.

4. Reviewing System Logs

In some cases, the Jenkins version is logged during startup.

• Examine the Jenkins system logs. The location of these logs varies depending on your system configuration but is frequently found in /var/log/jenkins/jenkins.log or similar.
• Search for lines containing “Jenkins” and “version”. The version number should be present in the startup messages.

This method is particularly useful when diagnosing startup issues or when you don’t have direct access to the Jenkins instance through the web interface or command line.

5. Using the jenkins-cli.jar (More Detailed)

As mentioned earlier, the jenkins-cli.jar is your best bet.

• Download the jenkins-cli.jar from your Jenkins instance (usually accessible at http://your_jenkins_url/jnlpJars/jenkins-cli.jar).
• Execute the command: java -jar jenkins-cli.jar -s http://your_jenkins_url/ help. Ensure you replace http://your_jenkins_url/ with the actual URL of your Jenkins instance.

This approach ensures you’re getting the version information directly from the running Jenkins instance.

Frequently Asked Questions (FAQs)

1. Why do I need to know the Jenkins version?

Knowing the Jenkins version is essential for several reasons: troubleshooting problems, ensuring compatibility with plugins, planning upgrades, and addressing security vulnerabilities. Different versions have different features, bug fixes, and security patches.

2. Where can I download the jenkins-cli.jar?

You can download the jenkins-cli.jar directly from your Jenkins instance. Typically, it’s accessible at http://your_jenkins_url/jnlpJars/jenkins-cli.jar, replacing http://your_jenkins_url/ with your actual Jenkins URL.

3. What if I don’t have access to the Jenkins web interface?

If you lack web interface access, utilize the Jenkins CLI, the REST API, or examine the Jenkins war file or system logs. These methods provide alternative ways to determine the version without requiring GUI access.

4. Can I find the Jenkins version without using the command line?

Yes, you can find the Jenkins version through the web interface (if accessible), or by examining the MANIFEST.MF file within the Jenkins war file.

5. How do I upgrade my Jenkins instance?

Upgrading Jenkins involves several steps: backing up your existing configuration, downloading the latest war file, replacing the existing war file, and restarting Jenkins. Refer to the official Jenkins documentation for detailed instructions. Always test the upgrade in a non-production environment first.

6. What are the risks of running an outdated Jenkins version?

Running an outdated Jenkins version exposes you to several risks: security vulnerabilities, compatibility issues with plugins, and lack of access to new features and bug fixes. Regularly updating Jenkins is crucial for maintaining a secure and stable environment.

7. How do I check if a specific plugin is compatible with my Jenkins version?

The Jenkins plugin index (available on the Jenkins website) lists the required Jenkins version for each plugin. Check the plugin’s documentation or entry in the plugin index to verify compatibility before installing or upgrading a plugin.

8. What does the Jenkins REST API provide beyond version information?

The Jenkins REST API provides access to a wide range of information and functionality: job status, build results, system configuration, and user management. It allows you to integrate Jenkins with other tools and automate various tasks.

9. How do I find the location of the jenkins.war file on my Linux system?

The location of the jenkins.war file depends on your installation method. Common locations include: /var/lib/jenkins, /usr/share/jenkins, or /opt/jenkins. You can also use the find command to locate the file: find / -name jenkins.war.

10. What’s the difference between LTS and weekly release Jenkins versions?

LTS (Long-Term Support) versions are released every 12 weeks and provide stability and reliability, with bug fixes and security patches applied over a longer period. Weekly releases offer the latest features and improvements but may be less stable. Choose the version that best suits your needs and risk tolerance.

11. How can I automate the process of checking the Jenkins version?

You can automate the process of checking the Jenkins version using scripting:

• Use curl to access the REST API.
• Parse the JSON output to extract the version number.
• Create a script that runs periodically (e.g., using cron) and sends an alert if the version is not as expected.

12. I am seeing a different version of Jenkins on UI and CLI. How can I fix it?

If you are experiencing different Jenkins versions on UI and CLI, then there is a high probability that there are two instances running with different versions. Restart your Jenkins server through UI to synchronize the version. You can also check the installed Jenkins version through REST API. In addition, examine the PATH variables in the Jenkins environment to ensure the correct Java version and jenkins-cli.jar are being used.