Confluence doesn't start due to 'Duplicate plugin found'
Platform Notice: Data Center Only - This article only applies to Atlassian products on the Data Center platform.
Note that this KB was created for the Data Center version of the product. Data Center KBs for non-Data-Center-specific features may also work for Server versions of the product, however they have not been tested. Support for Server* products ended on February 15th 2024. If you are running a Server product, you can visit the Atlassian Server end of support announcement to review your migration options.
*Except Fisheye and Crucible
Summary
After recently installing a plugin either by placing the jar file in <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory or via the Administration > Plugins page, confluence fails to start up.
Diagnosis
The atlassian-confluence.log file contains:
2010-03-27 12:34:16,237 ERROR [main] [atlassian.confluence.event.ConfluenceEventManager] publishEvent An exception was encountered while processing the event: com.atlassian.confluence.event.events.admin.ConfluenceReadyEvent[source=com.atlassian.confluence.upgrade.impl.DefaultUpgradeManager@56be1a11]
java.lang.RuntimeException: Error initialising plugin manager: Duplicate plugin found (installed version is the same or older) and could not be unloaded: 'com.pantero.confluence.plugins.testplans'
at com.atlassian.confluence.plugin.ConfluencePluginManager.processConfluenceReadyEvent(ConfluencePluginManager.java:276)
at com.atlassian.confluence.plugin.ConfluencePluginManager.onApplicationEvent(ConfluencePluginManager.java:177)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
...
at $Proxy8.publishEvent(Unknown Source)
at com.atlassian.confluence.upgrade.impl.DefaultUpgradeManager.upgrade(DefaultUpgradeManager.java:73)
...
Caused by: com.atlassian.plugin.PluginParseException: Duplicate plugin found (installed version is the same or older) and could not be unloaded: 'com.pantero.confluence.plugins.testplans'
at com.atlassian.plugin.manager.DefaultPluginManager.addPlugins(DefaultPluginManager.java:482)
at com.atlassian.plugin.manager.DefaultPluginManager.init(DefaultPluginManager.java:166)
at com.atlassian.confluence.plugin.ConfluencePluginManager.init(ConfluencePluginManager.java:163)
at com.atlassian.confluence.plugin.ConfluencePluginManager.processConfluenceReadyEvent(ConfluencePluginManager.java:272)
... 46 more
Caused by: com.atlassian.plugin.PluginException: Plugin is not uninstallable: com.pantero.confluence.plugins.testplans
at com.atlassian.plugin.manager.DefaultPluginManager.ensurePluginAndLoaderSupportsUninstall(DefaultPluginManager.java:399)
at com.atlassian.plugin.manager.DefaultPluginManager.unloadPlugin(DefaultPluginManager.java:379)
at com.atlassian.plugin.manager.DefaultPluginManager.uninstall(DefaultPluginManager.java:352)
at com.atlassian.plugin.manager.DefaultPluginManager.updatePlugin(DefaultPluginManager.java:555)
at com.atlassian.plugin.manager.DefaultPluginManager.addPlugins(DefaultPluginManager.java:476)
... 49 more
Cause
When confluence starts up it loads the classpath plugin first and then discovers that there is a newer version of the plugin in the database. In order to install the new version it first needs to uninstall the old one, but because it is a 'classpath' plugin it cannot be uninstalled hence the exception.
A similar issue was discovered at CONF-14126, however this is not considered a bug as plugins in Confluence should not be installed via the classpath (i.e. put in the <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory). They should be only installed via the Administration >> Plugins page within the Confluence Administration.
Solution
Remove the plugin from the <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory and restart Confluence.
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