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Java statistics monitoring (jstat) tool

Use the jstat tool to obtain Java Virtual Machine (JVM) statistics. The tool is similar to the HotSpot tool of the same name; the Eclipse OpenJ9™ version of jstat is an independent implementation, added for compatibility.

The command syntax is as follows:

jstat [<option>] [<vmid>]

where vmid is the Attach API virtual machine identifier for the Java process. This ID is typically the same as the operating system process ID, unless you specified the system property when you started the process.

VMID is shown in Java process status (jps) tool or other Attach API-based tools.

On its own, jstat prints help information. The values for <option> are as follows:

  • -J: supplies arguments to the JVM that is running the jstat command. You can use multiple -J options, for example: jstat -J-Xmx10m
  • -h: prints help information
  • -options: lists the available command options
  • -class: displays classloading statistics

The output has the following format:

Class Loaded    Class Unloaded
         860                 0


  • This tool is not supported and is subject to change or removal in future releases.
  • Although similar in usage and output to the HotSpot tool of the same name, this tool is a different implementation that is specific to OpenJ9. For more information about differences, see Switching to OpenJ9.

The tool uses the Attach API, and has the following limitations:

  • Displays information only for local processes that are owned by the current user, due to security considerations.
  • Displays information for OpenJ9 Java processes only
  • Does not show information for processes whose Attach API is disabled. Note: The Attach API is disabled by default on z/OS.

For more information about the Attach API, including how to enable and secure it, see Java Attach API.