Frequently Asked Questions
Description: This section lists Frequently Asked Questions about JDK Mission Control.

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# 4 Frequently Asked Questions

This section lists Frequently Asked Questions about JDK Mission Control.

I cannot connect to the JVM. What could be the problem?

Consider the following:

- Are you using the correct protocol?

  Ensure that you are using the same version of the JVM that you want to monitor as is being used by the JVM running the JMC client.

  The format of the service URL is:

  `service:jmx:rmi:///jndi/rmi://<hostname>/jmxrmi`

- Are the correct ports opened?

  Note that running JMX over RMI requires two ports and that one of the ports will not be known beforehand.

- Is the communication caught in a firewall?

  For more information, see JDK Mission Control Communications.

When attempting to connect to a JVM, I get a stack trace indicating that the JVM attempts to communicate with a strange IP or host name. What does this mean?

Sometimes RMI can have a problem determining which address to use. This can happen because of any of the following:

- There are access restrictions in the Security manager.

- The machine is multihomed and RMI is selecting the wrong interface.

- There is a misconfigured hosts file or a number of different network related configuration problems.

If all else fails, you can try specifying the `java.rmi.server.hostname` system property. Note that this can affect applications running on the JVM.

I am getting exceptions during startup about classes not being found. What is wrong?

Why does JDK Mission Control fail to find any local JVMs?

Consider the following:

- If you are running JMC from Eclipse, make sure that Eclipse is running on a JDK (not JRE).

- Make sure that there is a directory named `hsperfdata_username` in the system's `tmp` directory, that it is writable by the user running JMC, and that the file system supports access control lists (ACLs).

- Make sure you are running Mission Control on JDK version 11 or greater. You can set the JDK bin directory either by `PATH` environment variable, or by adding `-vm` parameter to `jmc.ini` file (must be inserted before `-vmargs` section).

How do I connect to JBoss?

Before starting JMC, you need to add the `-Xbootclasspath/a` option to the `-vmargs` section of the `jmc.ini` file. The value for this option (after a colon) should be set to the extended classpath that is generated by JBoss's `jconsole.bat` file (for this, add `@echo` on to the file and run it).

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