Steps to Troubleshoot Typical Java Problems

Steps To Troubleshoot Typical Java Problems

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This section list some typical java problems and the actions we need to perform, the tools we need to use to collect more information and/or to analyse and debug the problem.

• Hung, Deadlocked, or Looping Process
• Post-mortem Diagnostics
• Monitoring
• Actions on a Remote Debug Server
• Other Functions

Hung, Deadlocked, or Looping Process

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• Print thread stack for all Java threads.
  • Control-\
• Print thread trace for a process.
  • kill -QUIT pid
  • jstack -F pid (with -F option if pid does not respond)
• Detect deadlocks.
  • JConsole tool, Threads tab
  • Print information on deadlocked threads: Control-\
  • Print lock information for a process: jstack -l pid
• Get a heap histogram for a process.
  • Start Java process with -XX:+PrintClassHistogram, then Control-\
  • Start Java process with -XX:+PrintClassHistogram, then kill -QUIT pid
  • jmap -histo pid (with -F option if pid does not respond)
• Dump Java heap for a process in binary format to file.
  • jmap -dump:format=b,file=filename pid (with -F option if pid does not respond)
• Print shared object mappings for a process.
  • jmap pid
• Print heap summary for a process.
  • jmap -heap pid
• Print finalization information for a process.
  • jmap -finalizerinfo pid
• Attach the command-line debugger to a process.
  • jdb -connect sun.jvm.hotspot.jdi.SAPIDAttachingConnector:pid=pid
• Attach the command-line debugger to a core file on the same machine.
  • jdb -connect sun.jvm.hotspot.jdi.SACoreAttachingConnector:javaExecutable=path,core=corefile
• Attach the command-line debugger to a core file on a different machine.
  • On the machine with the core file: jsadebugd path corefile
    and on the machine with the debugger: jdb -connect sun.jvm.hotspot.jdi.SADebugServerAttachingConnector:debugServerName=machine

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Post-mortem Diagnostics

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• Examine the fatal error log file. Default file name is hs_err_pidpid.log in the working-directory.
• Create a heap dump.
  • HPROF: java -agentlib:hprof=file=file,format=b application; then Control-\
  • HPROF: java -agentlib:hprof=heap=dump application
  • JConsole tool, MBeans tab
  • Start VM with -XX:+HeapDumpOnOutOfMemoryError; if OutOfMemoryError is thrown, VM generates a heap dump.
• Browse Java heap dump.
  • jhat heap-dump-file
• Dump Java heap from core file in binary format to a file.
  • jmap -dump:format=b,file=filename corefile
• Get a heap histogram from a core file.
  • jmap -histo corefile
• Print shared object mappings from a core file.
  • jmap corefile
• Print heap summary ffrom a core file.
  • jmap -heap corefile
• Print finalization information from a core file.
  • jmap -finalizerinfo corefile
• Print Java configuration information from a core file.
  • jinfo corefile
• Print thread trace from a core file.
  • jstack corefile
• Print lock information from a core file.
  • jstack -l corefile

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Monitoring

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• Print statistics on the class loader.
  jstat -classvmID
• Print statistics on the compiler.
  • Compiler behavior: jstat -compiler vmID
  • Compilation method statistics: jstat -printcompilation vmID
• Print statistics on garbage collection.
  • Summary of statistics: jstat -gcutil vmID
  • Summary of statistics, with causes: jstat -gccause vmID
  • Behavior of the gc heap: jstat -gc vmID
  • Capacities of all the generations: jstat -gccapacity vmID
  • Behavior of the new generation: jstat -gcnew vmID
  • Capacity of the new generation: jstat -gcnewcapacity vmID
  • Behavior of the old and permanent generations: jstat -gcold vmID
  • Capacity of the old generation: jstat -gcoldcapacity vmID
  • Capacity of the permanent generation: jstat -gcpermcapacity vmID
• Monitor objects awaiting finalization
  • JConsole tool, Summary tab
  • jmap -finalizerinfo pid
  • getObjectPendingFinalizationCount method in java.lang.management.MemoryMXBean class
• Monitor memory
  • Heap allocation profiles via HPROF: java -agentlib:hprof=heap=sites
  • JConsole tool, Memory tab
  • Control-\ prints generation information.
• Monitor CPU usage.
  • By thread stack: java -agentlib:hprof=cpu=samples application
  • By method: java -agentlib:hprof=cpu=times application
  • JConsole tool, Overview and Summary tabs
• Monitor thread activity: JConsole tool, Threads tab
• Monitor class activity: JConsole tool, Classes tab

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Actions on a Remote Debug Server

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First, attach the debug daemon jsadebugd, then execute the command.

• Dump Java heap in binary format to a file: jmap -dump:format=b,file=filename hostID
• Print shared object mappings: jmap hostID
• Print heap summary : jmap -heap hostID
• Print finalization information : jmap -finalizerinfo hostID
• Print lock information : jstack -l hostID
• Print thread trace : jstack hostID
• Print Java configuration information: jinfo hostID

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Other Functions

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• Interface with the instrumented Java virtual machines.
  • Monitor for the creation and termination of instrumented VMs: jstatd daemon
  • List the instrumented VMs: jps
  • Provide interface between remote mointoring tools and local VMs: jstatd daemon
• Print Java configuration information from a running process.
  • jinfo pid
• Dynamically set, unset, or change the value of certain Java VM flags for a process.
  • jinfo -flag flag
• Pass a Java VM flag to the virtual machine.
  • jhat -Jflag ...
  • jmap -Jflag ...
• Print statistics of permanent generation of Java heap, by class loader.
  • jmap -permstat
• Report on monitor contention.
  • java -agentlib:hprof=monitor=y application
• Evaluate or execute a script in interactive or batch mode.
  • jrunscript
• Interface dynamically with an MBean, via JConsole tool, MBean tab:
  • Show tree structure.
  • Set an attribute value.
  • Invoke an operation.
  • Subscribe to notification.