locating blocked port

[Haines Brown]

I have an  application that refuses to start because  its port is 
blocked. But I have difficulty knowing what port it is

   $ java -jar /usr/local/share/JabRef/JabRef-3.2.jar &
  [1] 4831
  haines@lenin:~$ Jan 31, 2023 8:36:39 AM  
net.sf.jabref.logic.remote.server.Remote
  ListenerServerLifecycle open
  WARNING: Port is blocked
  java.net.BindException: Address already in use
        at java.base/sun.nio.ch.Net.bind0(Native Method)
        at java.base/sun.nio.ch.Net.bind(Net.java:555)
        at java.base/sun.nio.ch.Net.bind(Net.java:544)
        at java.base/sun.nio.ch.NioSocketImpl.bind(NioSocketImpl.java:643)
        at java.base/java.net.ServerSocket.bind(ServerSocket.java:388)
        at java.base/java.net.ServerSocket.<init>(ServerSocket.java:274)
        at 
net.sf.jabref.logic.remote.server.RemoteListenerServer.<init>(RemoteListenerServer.java:40)
        at 
net.sf.jabref.logic.remote.server.RemoteListenerServerThread.<init>(RemoteListenerServerThread.java:33)
        at 
net.sf.jabref.logic.remote.server.RemoteListenerServerLifecycle.open(RemoteListenerServerLifecycle.java:41)
        at net.sf.jabref.JabRef.start(JabRef.java:137)
        at net.sf.jabref.JabRefMain.main(JabRefMain.java:8)

  Arguments passed on to running JabRef instance. Shutting down.

How do I know from this what port the java application tried to use?

I try:

  $ strings $(which jabref) | wc -l
    56

  So I try:

    $ sudo ss -pt state listening 'sport = :56'
    Recv-Q   Send-Q    Local Address:Port   Peer Address:Port Process
    
  This seems a null return. Dores this mean jabref is not using port 
  56?


-- 

     Haines Brown 
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