Debian is broken.  I installed X2Go and FreeNX and then I needed to reboot but couldn’t because the shutdown program was not installed.  I installed that, rebooted, but somehow the virtual machine was corrupted beyond restoration.  I’m recovering from a backup but it will take some more work to get everything back to current so this machine may be down overnight.  Please use Ubuntu or Mint if you need a Debian-based machine in the meantime.