Re: No DISPLAY set in -X Tunneling

From: Edwin Johnson (elj_at_jflight.elj.org)
Date: 04/22/05 

Date: 22 Apr 2005 16:55:03 GMT

On 2005-04-22, Richard E. Silverman <res@qoxp.net> wrote:
>
> client or server (they are both "hosts"). However, two things suggest you
> have a basic misunderstanding;

It is certainly true that I may have a misunderstanding of how it operates.

> In SSH forwarding, the SSH *client* is running an X server (i.e. has an X
> display). The X forwarding allows X clients running on the SSH server to
> use the SSH client's display. The "xauth generate" command establishes a
> new X security key for use with this session, and so naturally talks to

Here is my understanding:

I am at the local machine, hence the client machine and running X with an X
display.

I type 'ssh -vvvX 192.168.1.12' to log into the remote machine, hence the
server, and to tunnel X through port 22 to my local, client machine.

In the words of the man page:
--------------
...user is using X11 (the DISPLAY environment variable is set), the
connection to the X11 display is automatically forwarded to the remote side
in such a way that any X11 programs started from the shell (or command) will
go through the encrypted channel, and the connection to the real X server

The DISPLAY value set by ssh will point to the server machine, but with a
display number greater than zero. This is normal, and happens because ssh
creates a ``proxy'' X server on the server machine for forwarding the
connections over the encrypted channel.

ssh will also automatically set up Xauthority data on the server machine.
For this purpose, it will generate a random authorization cookie, store it
in Xauthority on the server, and ve
---------------

Now I understand this to mean that the remote, server machine runs xauth and
writes to the .Xauthority file on the server machine or at least somewhere
else on that machine. In addition it also sets the DISPLAY environmental
label.

Thus, since I am logged in to the remote, server machine, I should be able
to type 'echo $DISPLAY' and see the new DISPLAY setting. (This was also
pointed out in another trouble shooting article which I read.)

Even though I log in successfully to the remote, server machine none of this
happens - the file doesn't appear to be written nor DISPLAY set on the
remote server machine.

Now I may be in error on my reading and interpretation of the man pages, but
this is my take on the events. The end result is that if I try and run an X
app after being logged in, the error 'Can't open display' happens.

Comments or suggestions?

...Edwin 

-- 
_______________________________________________________
"Once you have flown, you will walk the earth with your
eyes turned skyward, for there you have been, there you
long to return."-- da Vinci     ... www.shreve.net/~elj

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