x2x sharing problem i karmic

[Claus Lensbøl]

I've been using x2x under ubuntu 8.10 and 9.04 to share mouse and keyboard between multiple pc's, but it doesn't seem to work in karmic.

i run on master pc:
ssh -X *USER*@*IP-ADDRESS-SLAVE* x2x -west -to :0

I used to get a password promt and after typing pass, it just worked. Now I get a password promt and an error:

No protocol specified
x2x - error: can not open display :0

When I search the error, people are talking about /etc/gdm/gdm.conf but that file is not present (in karmic?).

x2x is really a great tool and I use it allot, so I hope there's a fix :)

[Brian Murray (brian-murray)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This bug did not have a package associated with it, which is important for ensuring that it gets looked at by the proper developers. You can learn more about finding the right package at https://wiki.ubuntu.com/Bugs/FindRightPackage. I have classified this bug as a bug in x2x.

When reporting bugs in the future please use apport, either via the appropriate application's "Help -> Report a Problem" menu or using 'ubuntu-bug' and the name of the package affected. You can learn more about this functionality at https://wiki.ubuntu.com/ReportingBugs.

[Claus Lensbøl (cmol)]

Thanks Brian. I don't quite know the bug reporting process yet :)

In this case I really don't know if it's a bug in x2x. The version haven't changed since jaunty, so it could just as well be a bug in gdm, or ufw for what I know?

[Robert C Jennings (rcj)]

I found a way to make x2x work, I wouldn't call it a solution but it points to what is missing when you get this error. The xauth authority file used when tunneling X through ssh does not have the cookie for the X server.

Setup:
 - 2 machines, called 'desktop' and 'laptop' where x2x is run on the laptop.
 - Run 'ssh -XC laptop x2x -east -to :0.0' from desktop
 - Error seen: 'x2x - error: can not open display :0'

From the desktop:
# ssh -X laptop 'xauth info'
Authority file: /home/user/.Xauthority
File new: no
File locked: no
Number of entries: 2
Changes honored: yes
Changes made: no
Current input: (argv):1

# ssh -X laptop 'xauth list'
laptop/unix:10 MIT-MAGIC-COOKIE-1 84924c4306f8234702fe1cec2c821c8f

From the laptop:
# xauth info
Authority file: /var/run/gdm/auth-for-user-w9KmhU/database
File new: no
File locked: no
Number of entries: 1
Changes honored: yes
Changes made: no
Current input: (argv):1

# xauth list
laptop/unix:0 MIT-MAGIC-COOKIE-1 007d71f327f9cf279ff3c5fb9d21b5a7

At this point the ssh session from the desktop to the laptop has a cookie for display :10 only. So the message regarding a failure to open :0 isn't a big surprise. I resolved this by running the following from the desktop:

# ssh -X laptop 'xauth merge /var/run/gdm/auth-for-user-w9KmhU/database'

After this is run, you can check that the cookie has been added for :0 by running:

# ssh -X laptop 'xauth list'
laptop/unix:0 MIT-MAGIC-COOKIE-1 007d71f327f9cf279ff3c5fb9d21b5a7
laptop/unix:10 MIT-MAGIC-COOKIE-1 84924c4306f8234702fe1cec2c821c8f

From there I can run:

# ssh -X laptop 'x2x -east -to :0.0'

Here's the caveat, the cookie (and the file it's stored in) for :0 changes each time you log in on the remote machine (in this case, 'laptop'). Here's the output on the laptop after logging out and back into X.

# xauth info
Authority file: /var/run/gdm/auth-for-user-u4JpYD/database
File new: no
File locked: no
Number of entries: 1
Changes honored: yes
Changes made: no
Current input: (argv):1

# xauth list
laptop/unix:0 MIT-MAGIC-COOKIE-1 149afc922a496cae086650e10f113bf5

At this point, the command 'ssh -X laptop x2x -east -to :0.0' will again fail. I cleaned up by running 'ssh -X laptop xauth remove laptop/unix:0' so that I only had a cookie entry for :10 at this point.

I don't have a real solution, but I hope this helps improve the understanding of the problem.

[Robert C Jennings (rcj)]

#!/bin/bash
## This is provided as a example of the steps required to work-around this issue.
## I am worried that it will get less attention with a workaround provided, but
## someone is going to do it, so here it is.

HOST=laptop
USER=user

## Add the cookie for :0 to the xauth file
## NOTE: This assumes that there is only one /var/run/gdm/auth-for-${USER}* directory
ssh -XC ${USER}@${HOST} 'xauth merge /var/run/gdm/auth-for-${USER}*/database'
# ssh -XC ${USER}@${HOST} 'xauth list'

## Run x2x on the remote host
## NOTE: This assumes that the desktop on the remote host is :0.0
ssh -XC ${USER}@${HOST} 'x2x -east -to :0.0'

## Remove the cookie for :0 from the xauth file
## NOTE: This assumes that the desktop on the remote host is :0.0
ssh -XC ${USER}@${HOST} 'xauth remove ${HOST}/unix:0'
# ssh -XC ${USER}@${HOST} 'xauth list'

[David Boersma (david-boersma)]

@Brian, Claus: at ubuntuforums it was suggested (http://ubuntuforums.org/showthread.php?t=1309289) that this is maybe (indeed) more a gdm issue than an x2x issue.

@Robert: I tried your workaround script and it works, thanks! I needed a little tweak though; our network administrator assigned a different static name to my laptop than I configured when installing Karmic. I need the network name to run ssh, but xauth uses the local install name. So I rewrote the script to:

#!/bin/bash
HOST=laptop-networkname
HOSTlocal=laptop-installname
USER=user

cmd1="xauth merge /var/run/gdm/auth-for-${USER}*/database"
cmd2="xauth list"
cmd3="x2x -west -to :0.0"
cmd4="xauth remove ${HOSTlocal}/unix:0"
ssh -XC ${USER}@${HOST} "$cmd1; $cmd2; $cmd3; $cmd4"
ssh -XC ${USER}@${HOST} "xauth list"

When I interrupt the script with ^C, cmd4 (xauth remove) apparently still gets executed, because the final xauth list shows only one entry, as desired.

Thanks!

[Sebastien Bacher (seb128)]

not sure I understand the description or care enough about that x2x thing to try to understand it but that doesn't seem a gdm bug

[Claus Lensbøl (cmol)]

Since the version of x2x haven changed since hardy (and x2x worked in jaunty), it must be a bug in gdm. Or a change at least.

Please tell what you don't understand, and I will try to clear it up to you.

[Sebastien Bacher (seb128)]

gdm is a login manager, it just let you enter login informations to start your session, it's not a ssh server or anything which should impact on what you do over ssh on that box

[Claus Lensbøl (cmol)]

Then I don't understand how David Boersma above made it work, with his script by doing changes to gdm?

ssh -XC ${USER}@${HOST} 'xauth merge /var/run/gdm/auth-for-${USER}*/database'

[Robert C Jennings (rcj)]

GDM is no longer storing the xauth info for the current login in /home/${USER}/.Xauthority, rather it is using /var/run/gdm/auth-for-${USER}*/database

As ssh uses the former for xauth keys, the x2x command run in the ssh environment will not find the existing key for the GDM session.

[Sebastien Bacher (seb128)]

not sure if that's a bug seems rather a decision from upstream, should be sent to GNOME

[Claus Lensbøl (cmol)]

Made a bug on gnome here:
https://bugzilla.gnome.org/show_bug.cgi?id=606201

[Sebastien Bacher (seb128)]

Thank you for sending the bug to GNOME

[David Boersma (david-boersma)]

FWIW: for me x2x works now the way it should, in Lucid, without having to resort to funny xauth tricks (like I had to with karmic). So on my desktop I just run:

ssh -XC username@laptop 'x2x -west -to :0.0'

and it does what i want it to do.

[Claus Lensbøl (cmol)]

I just testet et in lucid too. It works like a charm without any weird tricks.
Ran:
ssx -XC user@host x2x -west -to :0

This could be a Karmic only problem?