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Is there a programmatic way to turn on debugging in a running JVM instance? I am looking for an API that would make a running JVM, a debug server. The API would do the equivalent of 

-Xdebug -Xrunjdwp:transport=dt_socket,address=<host:port>,server=y,suspend=n.
Ranjit Iyer
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3 Answers3

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The debug port that the questioner refers to is for source code debugging, such as with an Eclipse debugger. The port for VisualVM is the JMX port, which takes a different set of JVM options. There are exceptions though: Mission Control for JRockit uses the jdwp port rather than the JMX port.

And yes, you can dynamically load the JMX debugger in code. Its complicated but OSGI can load this dynamically I believe. For example, here is a reference to Jetty project doing this.

djangofan
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You can attach to any running JVM using Visual VM. Be sure to download version 1.3.2 and install all the plugins.

duffymo
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  • +1 Correct! This should work at least when the JVM was started under the same user as VisualVM (or if permissions are appropriate). – Daniel Aug 04 '11 at 07:11
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This is not possible. The JVM has to know from the beginning that it is in debug mode. It runs a bit slower then but provides external processes with debug information and breakpoints which is not possible when the JVM already has been startet.

Daniel
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  • Daniel, I agree. I was hoping there was such an API. For what I am trying to achieve, I fully assume that the target JVM is not yet in debug mode, and that I would manage to get some code executed in it that would switch that VM to debug mode. After I know the exact port number the VM has started listening on, I would write that information to a well-known location that users of debuggers would consult and use for attaching their debuggers to that VM. – Ranjit Iyer Aug 04 '11 at 01:26