title: Java Heap Dump error - Metadata does not appear to be polymorphic
body: <p>I get this Stacktrace when trying to take a heap dump from a running Java process. What causes this and what do I have to do to make a proper heap dump? </p>
  
  <pre><code>Dumping heap to dump.bin ...
  Exception in thread "main" java.lang.reflect.InvocationTargetException
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:483)
      at sun.tools.jmap.JMap.runTool(JMap.java:201)
      at sun.tools.jmap.JMap.main(JMap.java:130)
  Caused by: java.lang.InternalError: Metadata does not appear to be polymorphic
      at sun.jvm.hotspot.types.basic.BasicTypeDataBase.findDynamicTypeForAddress(BasicTypeDataBase.java:278)
      at sun.jvm.hotspot.runtime.VirtualBaseConstructor.instantiateWrapperFor(VirtualBaseConstructor.java:102)
      at sun.jvm.hotspot.oops.Metadata.instantiateWrapperFor(Metadata.java:68)
      at sun.jvm.hotspot.memory.DictionaryEntry.klass(DictionaryEntry.java:71)
      at sun.jvm.hotspot.memory.Dictionary.classesDo(Dictionary.java:66)
      at sun.jvm.hotspot.memory.SystemDictionary.classesDo(SystemDictionary.java:190)
      at sun.jvm.hotspot.memory.SystemDictionary.allClassesDo(SystemDictionary.java:183)
      at sun.jvm.hotspot.utilities.HeapHprofBinWriter.writeClasses(HeapHprofBinWriter.java:942)
      at sun.jvm.hotspot.utilities.HeapHprofBinWriter.write(HeapHprofBinWriter.java:427)
      at sun.jvm.hotspot.tools.HeapDumper.run(HeapDumper.java:62)
      at sun.jvm.hotspot.tools.Tool.startInternal(Tool.java:260)
      at sun.jvm.hotspot.tools.Tool.start(Tool.java:223)
      at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
      at sun.jvm.hotspot.tools.HeapDumper.main(HeapDumper.java:83)
      ... 6 more
  </code></pre>
  
  <p>Environment: CentOS 64 bit, Java OpenJDK Runtime Environment (build 1.8.0_31-b13) OpenJDK 64-Bit Server VM (build 25.31-b07, mixed mode)</p>
  
  <p>Using <code>ps</code> to see the java version that is used:</p>
  
  <pre><code>/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.31-1.b13.el6_6.x86_64/jre/bin/java
  </code></pre>
  
  <p>My first try was:</p>
  
  <pre><code>/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.31-1.b13.el6_6.x86_64/bin/jmap  -dump:format=b,file=dump.bin 14984
  </code></pre>
  
  <p>That got me :</p>
  
  <pre><code>14984: Unable to open socket file: target process not responding or HotSpot VM not loaded
  The -F option can be used when the target process is not responding
  </code></pre>
  
  <p>So I ran with the <code>-F</code> option </p>
  
  <pre><code>/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.31-1.b13.el6_6.x86_64/bin/jmap -F -dump:format=b,file=dump.bin 14984
  </code></pre>