Types of Diagnostic Commands

Standard Commands

Standard commands are denoted by a green icon with the letter i in a circle. They provide general diagnostic information.

• JFR.check

  Prints the status of the running JFR recordings.

• JFR.dump

  Dumps the current data in the specified JFR recording to a recording file.

• JFR.stop

  Stops the specified JFR recording.

• VM.check_commercial_features

  Prints the status of commercial features.

• VM.command_line

  Prints the command line arguments that were used to start the JVM.

• VM.flags

  Prints the JVM flags and their current values.

• VM.system_properties

  Prints the system properties and their current values.

• VM.unlock_commercial_features

  Unlocks the commercial features.

• VM.uptime

  Prints the JVM uptime since it was launched.

• VM.version

  Prints the JVM version information.

• help

  Prints a list of available commands, help information for the specified command, or help for all commands.

Advanced Commands

Advanced commands are denoted by a yellow icon with an exclamation mark (!) in a triangle. They require more resources, can impact JVM performance, but provide more information.

• GC.run

  Calls the java.lang.System.gc() method that runs the garbage collector. Garbage collection performance depends on the size and contents of the Java heap.

• GC.run_finalization

  Calls the java.lang.System.runFinalization() method that runs the finalization methods of all objects pending finalization.

• JFR.start

  Starts a JFR recording.

• Thread.print

  Prints stack traces for all threads.

• VM.native_memory

  Prints native memory usage.

Internal Commands

Internal commands are denoted by a red icon with an exclamation mark (!) in an upside-down triangle. These provide very detailed diagnostic information, but greatly impact the JVM performance. Their impact depends on the size and contents of the Java heap.

• GC.class_histogram

  Prints detailed Java heap usage statistics.

• GC.class_stats

  Prints statistics about the Java class metadata. This command requires the -XX:+UnlockDiagnosticVMOptions to be enabled when starting the JVM.

• GC.heap_dump

  Generate a dump of the Java heap to an HPROF file.