From: rich@example.invalid   
      
   Harold Johanssen  wrote:   
   > On Sat, 22 Oct 2022 03:47:32 -0000 (UTC), Rich wrote:   
   >   
   >> Harold Johanssen  wrote:   
   >>>        I have a Slackware 15.0 host A running a TigerVNC session on   
   >>> display 1. I can connect to that session from another Slackware 15.0   
   >>> system with vncviewer tunneled within an sshSSH channel. I can also ssh   
   >>> into B from a terminal emulator in A.   
   >>>   
   >>>        What I would like to do is the following:   
   >>>   
   >>>        1. In the TigerVNC session in A launch a terminal emulator and   
   >>> ssh from it into B.   
   >>   
   >> You are telling this ssh here to perform X forwarding, right?  Or are   
   >> these systems on the same network such that B can contact A without   
   >> being carried over the ssh tunnel?   
   >>   
   >>>        2. At the ssh session in B created above send some graphical   
   >>> output to the TigerVNC session in A.   
   >>>   
   >>>        Step two does not work - I keep getting 'Can't open display: A:   
   >>> 1.0'.   
   >>>   
   >>>        I thought that the way to do pull this off consisted of   
   >>>        executing   
   >>> the following commands in a terminal emulator in the TigerVNC session   
   >>> in A:   
   >>>   
   >>>        $ export DISPLAY=A:1.0 $ xhost +B   
   >>   
   >> The xhost +B has to happen on A.  You need to tell A "allow B to use   
   >> your display", which is what "xhost +B" does, when run on A.  This above   
   >> looks like you are doing the xhost on B.   
   >   
   >        I don't think I have explained my situation properly. My   
   > apologies. Let me try again:   
   >   
   >        Host A is running an XFCE session that was launched in A with   
   > vncserver :1, vncserver being the TigerVNC X server.   
      
   Ok, that 'fine point' did not come across well in the original post.   
      
   Is The TigerVNC X server listening on a TCP port for remote X   
   connections?  Because if it is not, then you can't just do "DISPLAY=*"   
   on B and have apps on B connect to A (because to connect to A,   
   something on A has to be listening on the proper TCP port on A).   
      
   >        In that session I launched an xterm, and within this xterm I   
   > executed xhost +B, where B is the IP address if the other host involved.   
   > Both hosts can reach each other over ssh.   
      
   Reaching each other over ssh does not mean they can reach each other   
   over X11.  Nor does it mean they are on the same local network.  Are   
   they on the same local network, or are they separated on different   
   networks?   
      
   >        At this point I expected that when I launch an X application in   
   > the shell running in B, its output would be displayed in the XFCE session   
   > in A. It does not, with the diagnostic above.   
      
   If the TigerVNC server does not listen for remote X connections on a   
   TCP port on A, then this will not work.   
      
   Instead, try using ssh X forwarding (the -X or -Y options) which tunnel   
   the X protocol over the ssh connection, and which cause ssh to setup   
   the proper DISPLAY variable on B for you automatically.   
      
   >        The thing is, until recently I had an XFCE session running on A   
   > directly on top of Xorg, not TigerVNC's Xvnc - and the steps above worked   
   > as expected.   
      
   Likely because the real xorg was listening on a TCP port for remote X   
   connects (usually TCP 6000).  The TigerVNC server may not provide such   
   support at all, or it may be a CLI option to TigerVNC to cause it to   
   turn on "listen for external connections".   
      
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