How to Restart Jenkins Safely

1. Overview

In Jenkins, restarting the server is important as it is frequently required for updating the configurations and plugins to newer versions. Additionally, we want to approach this in a way that doesn’t disrupt our CI/CD pipeline. So, updating Jenkins needs a safe way to restart to avoid any bugs and errors as ongoing builds might get stuck during the restart.

In this tutorial, we’ll look at different ways to restart Jenkins safely to avoid job interruption and provide data integrity.

2. Restarting Jenkins

Jenkins is an open-source project that updates very frequently. So, we frequently need to update various components of the server, including the config or plugins. Let’s also look at various reasons to update the Jenkins server:

• Many Jenkins plugins need full server restarts
• Core configuration updates need a restart
• Server patches will also require a restart

Hence, restarting the Jenkins server needs to be done very carefully to ensure stability and prevent unexpected downtime.

3. Using the Built-in Safe Restart Option

Jenkins provides a built-in safe restart option which is used to restart the server without interrupting the running jobs. To demonstrate, let’s look at the following steps:

• Login to Jenkins with administrative privileges.
• Navigate to https://jenkins.example.org/safeRestart

Jenkins provides a restart banner for other Jenkins pages. Here, we can create a custom message that will appear on every page:

No new jobs will start and when all running jobs finish, the server will restart.

4. Using Jenkins CLI

The Jenkins CLI provides a way to programmatically restart the Jenkins server safely during automated tasks.

The Jenkins CLI is bundled as a JAR. We can download it from our deployment at https://jenkins.example.org/jnlpJars/jenkins-cli.jar link. To demonstrate, let’s take a look at the command:

$ java -jar jenkins-cli.jar -s https://jenkins.example.org -auth baeldung:baeldung_admin safe-restart

This will trigger the safe restart mode as before, meaning that no new jobs will start and the server will restart after all running jobs finish. This method is useful for remote management of Jenkins instances.

5. Using a Scripted Job for Scheduled Restarts

Another approach to restarting Jenkins is using a scripted job. This method is beneficial as it allows automated, scheduled restarts directly within Jenkins jobs without relying on external tools.

5.1. Using the System Groovy Step

To restart Jenkins safely with Groovy within a scheduled job, we can use the Jenkins Groovy plugin. It provides the required System Groovy script build step.

Now, let’s look at the steps to create a freestyle job and restart the server:

• Navigate to Jenkins Dashboard > New Item
• Select the Freestyle Project type and give it a name like “baeldung-restart”
• In the Build section, click Add Build Step and then Execute system Groovy script

Finally, for the script content, we need a fully-qualified reference to the safeRestart() system function:

jenkins.model.Jenkins.instance.safeRestart();

The above script will safely restart the Jenkins server on each run.

5.2. Schedule Restart

To automatically trigger the job, let’s configure the cron trigger in this job:

• Go to the Build Triggers section and select Build Periodically
• In the Schedule field, add the 0 0 * * * cron expression to restart Jenkins every day at midnight
• Click Save to apply the configuration

This scheduling also works across platforms without requiring additional installations and ensures the automatic and safe restart of the Jenkins server.

6. Conclusion

In this article, we explored several different ways to restart the Jenkins server safely. This includes the Jenkins UI, Jenkins CLI, or system Groovy scripts.

Finally, these methods let us restart Jenkins to finish server, plugin, or configuration updates without impacting existing running jobs.