Problems with X11 - Can't open display

You are trying too hard.

Just set "ForwardX11 yes" in ~/.ssh/config
Then ssh into your server.
There is no need to set any environment variables.

You DO NOT need xhost
You DO NOT need to set your own DISPLAY
You DO NOT need to mess with any config files.

The *ssh -X* is doing all the work. The localhost:10.0 was setup by the *ssh -X* option. This is an ssh tunnel for all your X11 traffic back to your Mac.

I use *ssh -X* every day at work talking to Linux boxes.

At worse, you might need to replace the -X with a -Y if the remote system is untrusted.

Are you still setting your own DISPLAY?

linux$ setenv DISPLAY <ip of mac>😮.0

Or are you using the DISPLAY environment variable established by ssh via the -X or -Y options.

In my previous reply, it looked to me you were doing good right up until you change DISPLAY and then tried using xhost.

I just *ssh -X* into my Linux box and that is all I need to do. DISPLAY is correctly setup by ssh. My DISPLAY generally looks like localhost:10.0 or some similar 10, 11, 12, ... display number. This is the local end of an ssh tunnel back to my Mac.

When you changed your DISPLAY environment variable, you totally bypassed all the work ssh did to make displaying X11 windows on your Mac easy.

Folks,
I think I found the problem and a solution.
After reading the following 2 items:
http://developer.apple.com/opensource/tools/runningX11.html
http://iparrizar.mnstate.edu/~juan/urania/2009/05/28/xquartz-on-macos-x-for-the- astronomer/

It looks that apple is migrating from X11 to Xorg it the latest Leopard versions (10.5.6 and 10.5.7)
More, when using http://xquartz.macosforge.org/ it's even more Xorg than before.

It seems thing got somehow reset to certain defaults with the 10.5.6 and/or 10.5.7 for Xorg and/or Apple's X11 somehow.

In a terminal do: "defaults read com.apple.x11" and "defaults read org.X.x11" (resp. Apple's X11 <10.5.6 and the X that comes IMHO with 10.5.6 or 10.5.7 and xquartz

There are for both options available and one of them is "nolisten_tcp".

From the first link mentioned above (runningx11) I distilled the following 2 terminal commands:
(on that page it says you can do this also with the X11 prefs, but I didn't test that)

defaults write com.apple.x11 nolisten_tcp -boolean false
defaults write org.X.x11 nolisten_tcp -boolean false

Restarted X....

Well,... my X on 10.5.7 is working again. with the xhost and DISPLAY variable mechanism.

Hope this helps
my 2 cents

I was having the same problem, been trying to figure it out for at least a week. Thanks a lot. Saved me a lot of trouble.

I'm still having problems even after the setting the "nolisten_tcp" to false. When I remote login to another mac, all running 10.5.7, I can't run a remote X11 window (e.g., xeyes). Things were working fine previously, so I assume this is something specific to 10.5.7. ForwardX11 yes is set on each machine. Doesn't matter if I log in with -X or -Y. I get the "Error: Can't open display" message. Any additional suggestions are greatly appreciated.

My bad. I had made changes in the /etc/ssh_config to ForwardX11 on all machines (all accounts already has the setting in the ~/.ssh/config file. The key was to change the /etc/sshd_config ForwardX11 to yes. With that changed, everything is working fine.

To allow me to ssh into my Mac Pro with 10.5.7 and run x applications (xclock, for example), all I had to do was change the sshd_config file to enable the "forward" lines.

I didn't have to do the other stuff with "defaults". In fact, typing those commands gave an error.

I'm ssh'ing into the mac pro from a windows computer, using putty, with X11 tunneling enabled.

I was having the same problems.
Wanting to connect my OSX macbook to a linux server.
The solution is as others have said. Add the forwarding command to the config files, and connecting with ssh -X user@remoteserver

Last step for me was to restart the ssh server, so that the config change would take effect. On my debian linux server, "/etc/init.d/ssh restart", or be low tech and just reboot 🙂