Add the following to the JVM options.
This means that when the JVM is started, it will listen on TCP port 5006 for remote java debugging.
In Intellij, you can set this up as a remote configuration. I kept the default values:
Debugger mode: attach
If the debug port is already in use, you may see the following error.
ERROR: transport error 202: bind failed: Address already in use ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510) JDWP exit error AGENT_ERROR_TRANSPORT_INIT(197): No transports initialized [debugInit.c:750] FATAL ERROR in native method: JDWP No transports initialized, jvmtiError=AGENT_ERROR_TRANSPORT_INIT(197)
Either change your port number, or find out what process is taking the port.