What causes VisualVM to report "CPU usage: unknown"?

Question

I am running a Java application on Java 17.0.0 from Azul - Zulu17.28+13-CA, with bundled JavaFX. Everything is working fine, except that the CPU usage simply says "unknown". I've seen messages before about "unavailable with this JVM" or something similar to that, when I ran VisualVM on older JDKs, but this is different.

VisualVM itself is running on JDK 19.0.1. About box reports: Azul 19.0.1; OpenJDK 64-Bit Server VM (19.0.1+10, mixed mode, sharing)

The same version of VisualVM running on JDK 19.0.1 on a different system is able to get CPU usage for an application running on Oracle JDK 8u60 (ancient, I know).

Does the Azul JVM that I am trying to monitor not support something to do with CPU monitoring that Oracle Java does?

Answer 1

As it turns out, the JRE that the application was running on was an image made with jlink that lacked the jdk.management module. When that module was added to the JRE, the CPU usage was reported properly.

More details at GH-479.