X windows display problem

[Thomas Chadwick]

>From: "Meredith Finkelstein" <meredith@www.honeybeerobotics.com>
>Reply-To: cygwin-xfree@cygwin.com
>To: "Thomas Chadwick" <j_tetazoo@hotmail.com>, cygwin-xfree@cygwin.com,   
>meredith@www.honeybeerobotics.com
>Subject: Re: X windows display problem
>Date: Tue, 3 Sep 2002 15:41:23 -0400

[snip]

>when i ssh and am on the remote host, and i echo the DISPLAY i get nothing.
>but i thought this was normal since i'm using the X flag with ssh.

This is not normal.  DISPLAY needs a value.  If ssh is not assigning one, 
there is probably something wrong with either ssh at the near end or sshd at 
the far end.

>when i set export the display=<localhost>:0.0 & then run xeyes
>then i get the following message
>Xlib: connection to "<localhost>:0.0" refused by server
>Xlib: No protocol specified
>
>Error: Can't open display: <localhost>:0.0

Try again.  From the ssh command-line on the remote machine, the correct 
value of DISPLAY should be <remotehost>:10.0, NOT <localhost>:0.0 AS YOU 
HAVE SHOWN HERE.  Here are a couple of diagrams to make my point...

With DISPLAY=localhost:0.0 on localhost, and DISPLAY=remotehost:10.0 on 
remotehost, the XClients on remotehost send their traffic through the 
encrypted channel (established between ssh and sshd) back to XWin on 
localhost:

    +--------------------+                 +------------------------+
    |     localhost      |                 |       remotehost       |
    +--------------------+                 +------------------------+
    |                    |                 |                        |
    | XWin <---> ssh <---+---(encrypted)---+---> sshd <---> XClient |
    |                    |                 |                        |
    +--------------------+                 +------------------------+


If you try to set DISPLAY=localhost:0.0 on remotehost, the XClients on 
remotehost try to talk directly to XWin on localhost and don't use the 
encrypted ssh channel at all:

    +--------------------+                 +------------------------+
    |     localhost      |                 |       remotehost       |
    +--------------------+                 +------------------------+
    |                    |                 |                        |
    | XWin <---> ssh <---+---(encrypted)---+---> sshd ---> XClient  |
    |   ^                |                 |                  ^     |
    |   |                |                 |                  |     |
    |   +----------------+--(unencrypted)--+------------------+     |
    |                    |                 |                        |
    +--------------------+                 +------------------------+


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