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There were 5 or 6 plugin updates for Jenkins v.1.476 which I have running on a Linux VM. The UI showed progress while updating as usual and I typically have to refresh the screen to see Jenkins reboot. However, this time it never restarted and was unresponsive. After refreshing a few times, it did show an error

Caused by: java.lang.NoClassDefFoundError: hudson/PluginManager$PluginUpdateMonitor at hudson.maven.PluginImpl.init(

According to the log the first failure appears while attempting to scout and then load hudson.maven.MavenModuleSet.

I also have Jenkins running on Windows and it is also not rebooting after updating plugins. I can restart it by running it in Java from the command line.

Has anyone seen this error or have any feedback on why it's happening? Thank you.

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Clearly there's an issue with the maven plugin. Do you actively use maven? Even if you do, you could try removing it at the very least to get the app up and running. – corsiKa Nov 20 '12 at 20:43
The Maven plugin is integrated into Jenkins/Hudson and is delivered as part of the core. Can you give more of the stack trace, and possibly the versions of plugins that are installed? – Toby Jackson Nov 20 '12 at 22:23
Updating Jenkins to the latest version (1.491) appears to have resolved the issue. At least there is no longer a plugin update for maven and all other updates are working. Thank you for the feedback. – Russell Nov 20 '12 at 22:28

This is a known bug, documented here.

It appears you can get around the issue (at least enough to get back into the GUI to revert the change) by deleting the $JENKINS_HOME/plugins/maven-plugin.jpi.pinned file. Standard rules about backing things up still apply.

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Hello evernat and welcome to SQA.SE. Consider adding some content from the linked article. See How to Answer for more details. – bytebuster Nov 25 '12 at 17:36

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