Again it seems that I have to answer my own question
But that is OK. By taking the time to define and post my question I have to some degree clarified the issue. Here are my lessons learned:
1 - If I launch the x2go client on my local machine and invoke a pre-configured remote session it seems to work fine. If I close the
X2CO CLIENT application the window containing the "view" of the remote session will close and the remote session will continue running. If I again launch the x2go client and invoke the remote session I am reconnected to the session which is running as I left it.
I do not know if this is the correct way; it does not seem very intuitive to have to close the parent x2go client to disconnect from a single remote session. But it seems to work reasonably well.
2 - If I have a connection to a remote session running and I [X] close the window containing the view of the remote session, the remote session continues to run. A logon dialog to that session appears in the blue "work area" if you will on the x2go client. If I attempt to logon generally it works the FIRST time. If I repeat the process it stalls with the connecting window showing. I see in the details "Session: Session terminated" although I can see over an ssh terminal that the programs which I had running in the remote session are still running. At this point I am stuck.
If I then CLOSE AND RELAUNCH THE CLIENT I can again connect to my remote session. I do not know if this is a bug or if I am using the program incorrectly.
3 - If I modify scenario 2 by canceling the logon dialog - which causes it to go back to the list of configured sessions on the right side of the x2go client - I can reconnect ONCE. After that I am again stuck. Closing and relaunching the x2go client allows me to connect again to my running remote session.
4 - DO NOT invoke the Session preferences... for a running but disconnected remote session. Even if the dialog is closed by Cancel. This seems to prevent reconnection to the remote session.
5 - If things get into such a state that it is impossible to recover and reconnect and it is necessary to reboot the remote machine... x2go will not create a new remote session. This can be resolved by opening the Session preferences... dialog and exiting with Save. It is not necessary to make any changes. However, this seems to clear some sort of stale data and will allow a remote session to be started.
6 - Be afraid, very afraid of selecting Full Screen on a remote session configuration if the local machine has multiple monitors. I have two monitors, one landscape and one portrait. When I invoked such a remote session it filled both monitors but I was unable access anything on the remote machine. I could not even get a terminal launched in order to reboot the remote machine. I physically did a hard shutdown on the remote machine but my local machine was filled with the dead remote session and unresponsive. Fortunately after a few minutes the x2go client shut down and I regained control of the local machine.
In conclusion... x2go is much more resource efficient that x11vnc. I cannot compare it to vnc4 or Tight/Tiger vnc as I have yet to get them to run on Ubuntu 20.04. The somewhat bizarre client operation makes accessing multiple remote machines problematic. The need to close and restart the x2go client to re-establish connections is especially limiting. N.B. It is possible to launch a second instance of the x2go client - on a different workspace for example - and then connect to another remote machine. This will allow independent connect, disconnect, restart client and reconnect.
That is what I have to offer. Perhaps it will help someone else.
Ken
