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Q: I am having problems building JMC core, more specifically with the JDP tests.

 AA: You may need to ask a local multicast route like so:

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A2: You should have a directory named hsperfdata_<user> in your tmp directory, where <user> is your login. (On windows you should be able to find this folder under C:\Users\myuser\AppData\Local\Temp\hsperfdata_myuser.) Make sure that the directory can be written to. Also make sure that you are using a file system that supports ACLs.A3: Double check the JAVA_HOME/lib/missioncontrol/jmc.ini file, the line after '-vm' should not be empty, but say './' (without the quotes). If you see this behavior, please write a post in this forum, so we can get gain some more understanding of this weird issue.

Q: I cannot access the Flight Recorder!

A1: Make sure you are trying to connect to a 7u40 or later.

A2: Make sure If running with an Oracle JDK < 11, ensure you have started the JVM you are trying to start recordings on with the proper flags: -XX:+UnlockCommercialFeatures -XX:+FlightRecorder 

Q: How do I install the Eclipse version?

A: Install Eclipse, then install the plug-ins from the update site. Either do that following the instructions in the README.txt and a local build, or from the update site provided by your favorite JMC vendor. 

Q: I want to connect to my 64-bit JVM from a 32-bit Mission Control (or vice versa)

A: Start the JMX agent on your JVM by adding the JVM flag -Dcom.sun.management.jmxremote 

Q: JMC on Mac OS X does not seem to start anymore.

A: Try removing your ~/.jmc folder. (If you still see this with JMC 5.3.0 or later, please let us know.)

Q: Why are there no I/O events in my JFR recording?

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A2: Did you disable the I/O events in your template?

Q: I've installed plug-ins in the JMC application, why can't I use them?

A: If you're using JMC 5.3, see the JMC 5.3 Release Notes for a work around. This should not happen in 5.4.0 or later. 

Q: Why do I get a lot fewer method samples then I expected?

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A: This can be a known JavaFX/GTK related issue (https://bugs.openjdk.java.net/browse/JDK-8089584), try setting this environment variable: SWT_GTK3=0

Q: Error message "Could not start JDP. Can't assign requested address"

A: Workaround: add "-Djava.net.preferIPv4Stack=true" to the JVM flags used to start JMC or Eclipse.

Q: I cannot connect

A: Consider the following:

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

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

A: Ensure that you are using JAVA_HOME/bin/jmc to start the JMC client. 

Q: Why does Java Mission Control fail to find any local JVMs?

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• Make sure that you are using JAVA_HOME/bin/jmc to start the JMC client.
• 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).

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Also, see the last chapter in the documentation included with JMC.