title: Jenkins fails to start after restart due to com.thoughtworks.xstream.mapper.CannotResolveClassException
body: <p>Jenkins version : Jenkins ver. 2.32.1
  Google Login Plugin version : 1.3</p>
  
  <p>I got this error after I restart my jenkins, can anyone suggest me how to solve it ?</p>
  
  <p>The thing is :</p>
  
  <p>-I already make sure that in plugins directory I had the google-login plugin enabled</p>
  
  <p>-I didn't change anything on the plugins, just straight restart</p>
  
  <p>-It's been so long since I restart my jenkins</p>
  
  <pre><code>hudson.util.HudsonFailedToLoad: org.jvnet.hudson.reactor.ReactorException: java.io.IOException: Unable to read /var/lib/jenkins/config.xml
      at hudson.WebAppMain$3.run(WebAppMain.java:248)
  Caused by: org.jvnet.hudson.reactor.ReactorException: java.io.IOException: Unable to read /var/lib/jenkins/config.xml
      at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:269)
      at jenkins.InitReactorRunner.run(InitReactorRunner.java:47)
      at jenkins.model.Jenkins.executeReactor(Jenkins.java:1110)
      at jenkins.model.Jenkins.&lt;init&gt;(Jenkins.java:926)
      at hudson.model.Hudson.&lt;init&gt;(Hudson.java:85)
      at hudson.model.Hudson.&lt;init&gt;(Hudson.java:81)
      at hudson.WebAppMain$3.run(WebAppMain.java:231)
  Caused by: java.io.IOException: Unable to read /var/lib/jenkins/config.xml
      at hudson.XmlFile.unmarshal(XmlFile.java:161)
      at jenkins.model.Jenkins.loadConfig(Jenkins.java:3015)
      at jenkins.model.Jenkins.access$1100(Jenkins.java:326)
      at jenkins.model.Jenkins$16.run(Jenkins.java:3033)
      at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
      at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
      at jenkins.model.Jenkins$7.runTask(Jenkins.java:1086)
      at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
      at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
      at java.lang.Thread.run(Thread.java:748)
  Caused by: jenkins.util.xstream.CriticalXStreamException: org.jenkinsci.plugins.googlelogin.GoogleOAuth2SecurityRealm : org.jenkinsci.plugins.googlelogin.GoogleOAuth2SecurityRealm
  ---- Debugging information ----
  message             : org.jenkinsci.plugins.googlelogin.GoogleOAuth2SecurityRealm
  cause-exception     : com.thoughtworks.xstream.mapper.CannotResolveClassException
  cause-message       : org.jenkinsci.plugins.googlelogin.GoogleOAuth2SecurityRealm
  class               : hudson.model.Hudson
  required-type       : hudson.model.Hudson
  converter-type      : hudson.util.RobustReflectionConverter
  path                : /hudson/securityRealm
  line number         : 485
  version             : not available
  -------------------------------
      at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:356)
      at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:270)
      at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
      at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
      at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
      at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
      at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
      at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
      at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1189)
      at hudson.util.XStream2.unmarshal(XStream2.java:114)
      at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1173)
      at hudson.XmlFile.unmarshal(XmlFile.java:159)
      ... 11 more
  Caused by: com.thoughtworks.xstream.mapper.CannotResolveClassException: org.jenkinsci.plugins.googlelogin.GoogleOAuth2SecurityRealm
      at com.thoughtworks.xstream.mapper.DefaultMapper.realClass(DefaultMapper.java:79)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.DynamicProxyMapper.realClass(DynamicProxyMapper.java:55)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.PackageAliasingMapper.realClass(PackageAliasingMapper.java:88)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.ClassAliasingMapper.realClass(ClassAliasingMapper.java:79)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.ArrayMapper.realClass(ArrayMapper.java:74)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.SecurityMapper.realClass(SecurityMapper.java:71)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at hudson.util.XStream2$CompatibilityMapper.realClass(XStream2.java:282)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at hudson.util.xstream.MapperDelegate.realClass(MapperDelegate.java:43)
      at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:30)
      at com.thoughtworks.xstream.mapper.CachingMapper.realClass(CachingMapper.java:48)
      at hudson.util.RobustReflectionConverter.determineType(RobustReflectionConverter.java:461)
      at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:327)
      ... 22 more
  </code></pre>