Configure X connections over TCP without using an X connection

Question

I want to run a GUI application on a remote machine I only have ssh access to. I don't need to, or want to, see the GUI window. (I know I could use something like ssh -C -X remote_server if I wanted the GUI to be on my client.)

I know X is running on the remote machine, as ps shows this:

root  ... /usr/bin/Xorg :0 -br -audit 0 -auth /var/gdm/:0.Xauth -nolisten tcp vt7

I set DISPLAY=:0.0 but I then get "Xlib: connection to ":0.0" refused by server" when I try to use it.

At Get remote x display working in linux without ssh tunneling and Xserver doesn't work unless DISPLAY=0.0 I see the advice to use gdmsetup to allow X to listen on TCP. But, gdmsetup is a GUI application! And trying to run it over ssh -X did not work ("X11 connection rejected because of wrong authentication").

So, is there a text file I can edit to remove -nolisten? And, after editing it, how do I safely restart X, remotely? (There is other stuff running on this machine, so requesting a reboot is possible, but undesirable.) If not, should gdmsetup be able to run over ssh and I should persevere in that direction?

UPDATE: I had to do the ssh -X session as root (ssh as a normal user, then sudo or su, does not work.) So, I did the edit with gdmsetup. I then restarted X with gdm-restart. I've also done xhost + from that ssh -X session. The ps line no longer shows the -nolisten tcp part. But still no luck connecting to it, with either DISPLAY=:0 or DISPLAY=localhost:0

UPDATE#2: I just noticed the reason xauth + hadn't helped (when done over ssh -X) was it altered my client machine, not the remote server! Oops. Good job I was inside the firewall! (I think the reason it had done this was related to the XAUTHORITY environmental variable, see Cougar's reply.)

Answer 1

as it seems you want your app to attach to the session root owns right now: the gdm - login screen.

why don't you just launch your own xserver and your program:

%> startx /your/program -- :1

(Added by Darren) Here is precisely what I did. In one ssh session, become root, and type:

startx -- :1 &
export DISPLAY=:1
xhost + &

Then in another ssh session, normal user:

export DISPLAY=:1
xclock

(Just using xclock as a test.)

Answer 2

If you just need to connect to the remotely running X display and start your program then it is just an authorization problem you have. Now it depends how the authorization is set up.

One way is to use xhost and give permissions per IP but this is highly unsecure because any programm running on this machine (or any machine if you just use +) can automatically connect with your X dislpay server.

The common way is to use X authority file. Then you just need to know this file and have an access to it. Now it depends on distribution if this file is .Xauthority in your home directory or is it some temporary file set up every time you start X session.

In first case everything works out of box, in latter case you need to know this temporary file name. One way to find it out is to look at XAUTHORITY variable in environment of some program (like windowmanager) already running under your X server. You can get environment variables easily from /proc/PID/environ file like this:

cat /proc/12345/environ | xargs -0 -L 1 echo | grep XAUTHORITY

Then just export XAUTHORITY and DISPLAY variables to your shell and start your program

Answer 3

It looks like you are going to a great length to make it work. As an alternative, I could recommend installing FreeNX on the remote machine and access it with NXClient. You will get a full remote desktop via ssh and you will be able just open terminal window and run your app. This will take less time then trying to figure out the tunneling with ssh.