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Diagnosing JVM Parameters in Java Applications with JPS

#jps #jvm #java #docker

When dealing with third-party Java applications where startup parameters are hard to verify, using the jps tool to confirm the actually effective JVM parameters is one of the most effective diagnostic methods. Here's a step-by-step guide:

1. Basic Process Identification 

jps -l -m -v
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  • Output Example: 
  12345 app.jar -Xmx2g -Dspring.profiles.active=prod
  67890 com.example.MainClass -Dconfig.path=/opt/conf
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  • Parameter Breakdown:
    • -l: Displays the full package name or JAR path.
    • -m: Outputs parameters passed to the main method.
    • -v: Shows JVM arguments.

2. Comparing Key Parameters

Expected Parameter JPS Verification Command Common Issue Scenarios
Heap Memory Configuration `jps -v grep -E 'Xmx
GC Algorithm Selection {% raw %}`jps -v grep 'Use.*GC'`
System Properties `jps -v grep 'Dproperty='`
Logging Configuration `jps -v grep 'logging.config'`

3. Advanced Diagnostic Techniques

3.1 Process Filtering 

# Finding a specific application process
jps -v | grep 'app-name-pattern'

# Real-time monitoring with pipes
watch -n 1 "jps -l -v | grep -v sun.tools.jps"
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3.2 Parameter Tracing 

# Locate the startup script path
ps -ef | grep java | grep -v grep | awk '{print $NF}'
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3.3 Dynamic Verification 

jinfo -flags <PID> 2>/dev/null | grep 'specific_param'
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  • Requires permissions to the JDK installation path.
  • Supports viewing non-standard parameters like CMS collector settings.

4. Handling Common Issues

Case 1: No Output from JPS

  • Cause: Missing tools.jar in JRE environment.
  • Solution: Install a full JDK instead of just JRE.

Case 2: Incomplete Parameter Display

  • Use combined commands: 
  jrunscript -e 'java.lang.management.ManagementFactory.getRuntimeMXBean().getInputArguments().forEach(print)'
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Case 3: Container Environment Limitations

  • Inside containers, run: 
  docker exec -it <container> /path/to/jps -v
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  • For Kubernetes: 
  kubectl exec <pod> -- jps -v
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5. Verification of Parameter Effectiveness

  1. Memory Verification: 
   jstat -gc <PID> 1000 5  # Monitor heap memory changes
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  1. GC Verification: 
   jstat -gcutil <PID> | awk '{print $6}'  # Observe GC type
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  1. System Properties Verification: 
   jinfo -sysprops <PID> | grep 'property.key'
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By deeply utilizing the jps tool chain, you can accurately identify issues like:

  • Parameter typos (e.g., -Xmx2048m misspelled as -Xmx2048).
  • Multi-level parameter overriding in startup scripts (environment variables > command-line args > config files).
  • Parameter invalidation due to container cgroup limits (like -Xmx exceeding container memory).
  • Framework default parameters overriding custom settings (common in Spring Boot's application.properties).

References:

tag

OOM
OutOfMemory

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