Actually, this seems not an x2go issue, but a linux mint issue : by default, there is a "xhost +" command launched at session startup for all users.

If you type "xhost - ", then you should see the normal behavior again : userB will get a "no desktop found" message if he try to connect to the x2go host.

So, the workaround is to remove the "xhost +" command in the Control Panel > Startup Applications for each user,

or completely remove the /etc/xdg/autostart/mint-xhost-plus.desktop (but this could come back if the package ubuntu-system-adjustments is updated)

or change this file to:

[Desktop Entry] Encoding=UTF-8 Version=1.0 Name=Xhost + Exec=xhost + Terminal=false Type=Application StartupNotify=false Terminal=false X-MATE-Autostart-enabled=false Hidden=true

note to x2go packages maintainer: Maybe this should be an option to check/disable when the x2goserver package is installed?

Or maybe a warning should be issued if "xhost" is set to + when a user connect?