Diagnosing JVM Parameters in Java Applications with JPS

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 <span>-l</span> <span>-m</span> <span>-v</span>
jps <span>-l</span> <span>-m</span> <span>-v</span>
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
  12345 app.jar -Xmx2g -Dspring.profiles.active=prod
  67890 com.example.MainClass -Dconfig.path=/opt/conf
  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

3. Advanced Diagnostic Techniques

3.1 Process Filtering

<span># Finding a specific application process</span>
jps <span>-v</span> | <span>grep</span> <span>'app-name-pattern'</span>
<span># Real-time monitoring with pipes</span>
watch <span>-n</span> 1 <span>"jps -l -v | grep -v sun.tools.jps"</span>
<span># Finding a specific application process</span>
jps <span>-v</span> | <span>grep</span> <span>'app-name-pattern'</span>

<span># Real-time monitoring with pipes</span>
watch <span>-n</span> 1 <span>"jps -l -v | grep -v sun.tools.jps"</span>
# 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

<span># Locate the startup script path</span>
ps <span>-ef</span> | <span>grep </span>java | <span>grep</span> <span>-v</span> <span>grep</span> | <span>awk</span> <span>'{print $NF}'</span>
<span># Locate the startup script path</span>
ps <span>-ef</span> | <span>grep </span>java | <span>grep</span> <span>-v</span> <span>grep</span> | <span>awk</span> <span>'{print $NF}'</span>
# Locate the startup script path
ps -ef | grep java | grep -v grep | awk '{print $NF}'

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3.3 Dynamic Verification

jinfo <span>-flags</span> <PID> 2>/dev/null | <span>grep</span> <span>'specific_param'</span>
jinfo <span>-flags</span> <PID> 2>/dev/null | <span>grep</span> <span>'specific_param'</span>
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 <span>-e</span> <span>'java.lang.management.ManagementFactory.getRuntimeMXBean().getInputArguments().forEach(print)'</span>
  jrunscript <span>-e</span> <span>'java.lang.management.ManagementFactory.getRuntimeMXBean().getInputArguments().forEach(print)'</span>
  jrunscript -e 'java.lang.management.ManagementFactory.getRuntimeMXBean().getInputArguments().forEach(print)'

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Case 3: Container Environment Limitations

• Inside containers, run:

  docker <span>exec</span> <span>-it</span> <container> /path/to/jps <span>-v</span>
  docker <span>exec</span> <span>-it</span> <container> /path/to/jps <span>-v</span>
  docker exec -it <container> /path/to/jps -v

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• For Kubernetes:

  kubectl <span>exec</span> <pod> <span>--</span> jps <span>-v</span>
  kubectl <span>exec</span> <pod> <span>--</span> jps <span>-v</span>
  kubectl exec <pod> -- jps -v

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5. Verification of Parameter Effectiveness

1. Memory Verification:

   jstat <span>-gc</span> <PID> 1000 5  <span># Monitor heap memory changes</span>
   jstat <span>-gc</span> <PID> 1000 5  <span># Monitor heap memory changes</span>
   jstat -gc <PID> 1000 5  # Monitor heap memory changes

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1. GC Verification:

   jstat <span>-gcutil</span> <PID> | <span>awk</span> <span>'{print $6}'</span>  <span># Observe GC type</span>
   jstat <span>-gcutil</span> <PID> | <span>awk</span> <span>'{print $6}'</span>  <span># Observe GC type</span>
   jstat -gcutil <PID> | awk '{print $6}'  # Observe GC type

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1. System Properties Verification:

   jinfo <span>-sysprops</span> <PID> | <span>grep</span> <span>'property.key'</span>
   jinfo <span>-sysprops</span> <PID> | <span>grep</span> <span>'property.key'</span>
   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:

• Oracle Documentation on JPS
• Java Tuning Guide

tag

OOM
OutOfMemory

原文链接：Diagnosing JVM Parameters in Java Applications with JPS