Make sure that JRebel installation folder doesn't contain spaces.

Generate the jrebel-bootstrap.jar by running java -jar $AGENT_PATH_WIN using the JVM you will run the application server with (you can also add this line to the startServer.sh after the environment is set).

Start the IBM WebSphere server and run the Administrative Console.

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In the Administration Console open Servers » Application Servers and select the server your app is deployed to.

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Select Java and Process Management» Process Definition.

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Select Java Virtual Machine.

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Insert the following line into Generic JVM arguments for Websphere 6.1 or later running on IBM JDK 5 or later:

-noverify -Xshareclasses:none -Xbootclasspath/p:$BOOTSTRAP_PATH_WIN;$AGENT_PATH_WIN

Insert the following line into Generic JVM arguments for Websphere 6.0 or later running on IBM JDK 1.4:

-noverify -Xbootclasspath/p:$BOOTSTRAP_PATH_WIN;$AGENT_PATH_WIN

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Press OK, when asked, Save the master configuration and restart the server.