Menu
We have an open beta of an app which occasionally causes the heapspace to overflow. The JVM reacts by going on a permanent vacation.
To analyze this I would like to peek into the memory at the point where it failed. Java does not want me to do this. The process is still in memory but it doesn't seem to be recognized as a java process.
The server in question is a debian Lenny server, Java 6u14
/opt/jdk/bin# ./jmap -F -dump:format=b,file=/tmp/apidump.hprof 11175 Attaching to process ID 11175, please wait... sun.jvm.hotspot.debugger.NoSuchSymbolException: Could not find symbol "gHotSpotVMTypeEntryTypeNameOffset" in any of the known library names (libjvm.so, libjvm_g.so, gamma_g) at sun.jvm.hotspot.HotSpotTypeDataBase.lookupInProcess(HotSpotTypeDataBase.java:390) at sun.jvm.hotspot.HotSpotTypeDataBase.getLongValueFromProcess(HotSpotTypeDataBase.java:371) at sun.jvm.hotspot.HotSpotTypeDataBase.readVMTypes(HotSpotTypeDataBase.java:102) at sun.jvm.hotspot.HotSpotTypeDataBase.<init>(HotSpotTypeDataBase.java:85) at sun.jvm.hotspot.bugspot.BugSpotAgent.setupVM(BugSpotAgent.java:568) at sun.jvm.hotspot.bugspot.BugSpotAgent.go(BugSpotAgent.java:494) at sun.jvm.hotspot.bugspot.BugSpotAgent.attach(BugSpotAgent.java:332) at sun.jvm.hotspot.tools.Tool.start(Tool.java:163) at sun.jvm.hotspot.tools.HeapDumper.main(HeapDumper.java:77) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at sun.tools.jmap.JMap.runTool(JMap.java:179) at sun.tools.jmap.JMap.main(JMap.java:110) Debugger attached successfully. sun.jvm.hotspot.tools.HeapDumper requires a java VM process/core! 
812
jmap tool is shipped with JDK. Here is how you should invoke it: jmap -dump:live,file=<file-path> <pid> where pid: is the Java Process Id, whose heap dump should be captured file-path: is the file path where heap dump will be written in to. Note: It's quite important that you pass the “live” option in the command line.
jmap is a tool to print statistics about memory in a running JVM. We can use it for local or remote processes. To capture a heap dump using jmap, we need to use the dump option: jmap -dump:[live],format=b,file=<file-path> <pid>
Jmap is the tool which gives you the possibility with one command to take the dump. The problem with that way is that it can take several minutes, even hours, to finish. It depends of the size of the configured java heap size.
The solution was very simple. I was running the jmap as root, but I had to run it as the user who started the jvm. I will now go hide my head in shame.
55
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
