How do you handle a Jenkins crash after a plugin update?

If you don't have a backup, you can manually recover by replacing the problematic plugin. First, identify the problematic plugin from the logs . Then, download a compatible version of that plugin from the Jenkins plugin repository (https://plugins.jenkins.io/) or from a trusted mirror. You need to ensure the version is compatible with your Jenkins core version . To replace the plugin, navigate to the JENKINS_HOME/plugins directory (usually /var/lib/jenkins/plugins), locate the plugin's .hpi or .jpi file, and replace it with the downloaded version . After replacement, restart Jenkins for the changes to take effect .

Jenkins can be started in a "safe mode" by temporarily disabling all plugins. To do this, create a temporary file called jenkins.install.InstallUtil.lastExecVersion in your JENKINS_HOME directory with the content being your Jenkins version number. Then restart Jenkins—it will start with plugins disabled. From there, you can navigate to the plugin manager and selectively disable or remove the problematic plugin . Once the issue is resolved, remove this file and restart Jenkins normally.

To prevent future crashes, always backup the JENKINS_HOME directory, especially the plugins folder, before performing any plugin updates . Test plugin updates in a non-production environment first . Maintain a version inventory of your plugins to track dependencies . Consider using a configuration as code approach to version-control your Jenkins configuration, making recovery faster. For production environments, enable the "Role-based Strategy" plugin and restrict permissions to minimize the impact of compromised plugins . Regularly update Jenkins core and plugins, but do so incrementally rather than all at once to isolate potential issues .