An X program needs two pieces of information in order to connect to an X display.
It needs the address of the display, which is typically :0 when you're logged in locally or :10, :11,
etc. when you're logged in remotely (but the number can change
depending on how many X connections are active). The address of the
display is normally indicated in the DISPLAY environment variable.
It needs the password for the display. X display passwords are called magic cookies.
Magic cookies are not specified directly: they are always stored in X
authority files, which are a collection of records of the form “display :42 has cookie 123456”. The X authority file is normally indicated in the XAUTHORITY environment variable. If $XAUTHORITY is not set, programs use ~/.Xauthority.
You're trying to act on the windows that are displayed on your
desktop. If you're the only person using your desktop machine, it's very
likely that the display name is :0. Finding the location
of the X authority file is harder, because with gdm as set up under
Debian squeeze or Ubuntu 10.04, it's in a file with a randomly generated
name. (You had no problem before because earlier versions of gdm used
the default setting, i.e. cookies stored in ~/.Xauthority.)
Here are a few ways to obtain the values of DISPLAY and XAUTHORITY:
You can systematically start a screen session from your desktop, perhaps automatically in your login scripts (from ~/.profile; but do it only if logging in under X: test if DISPLAY is set to a value beginning with : (that should cover all the cases you're likely to encounter)). In ~/.profile:
case $DISPLAY in
:*) screen -S local -d -m;;
esac
Then, in the ssh session:
screen -d -r local
You could also save the values of DISPLAY and XAUTHORITY in a file and recall the values. In ~/.profile:
case $DISPLAY in
:*) export | grep -E ' (DISPLAY|XAUTHORITY)=' >~/.local-display-coordinates.sh;;
esac
In the ssh session:
. ~/.local-display-coordinates.sh
screen
You could detect the values of DISPLAY and XAUTHORITY
from a running process. This is harder to automate. You have to figure
out the PID of a process that's connected to the display you want to
work on, then get the environment variables from /proc/$pid/environ (eval export $(</proc/$pid/environ tr \\0 \\n | grep -E '^(DISPLAY|XAUTHORITY)=')¹).
Another approach is to not try to obtain the value of $XAUTHORITY in the ssh session, but instead to make the X session copy its cookies into ~/.Xauthority. Since the cookies are generated each time you log in, it's not a problem if you keep stale values in ~/.Xauthority.
There can be a security issue if your home directory is accessible over NFS or other network file system that allows remote administrators to view its contents. They'd still need to connect to your machine somehow, unless you've enabled X TCP connections (Debian has them off by default). So for most people, this either does not apply (no NFS) or is not a problem (no X TCP connections).
To copy cookies when you log into your desktop X session, add the following lines to ~/.xprofile or ~/.profile (or some other script that is read when you log in):
case $DISPLAY:$XAUTHORITY in
:*:?*)
# DISPLAY is set and points to a local display, and XAUTHORITY is
# set, so merge the contents of `$XAUTHORITY` into ~/.Xauthority.
XAUTHORITY=~/.Xauthority xauth merge "$XAUTHORITY";;
esac
¹ In principle this lacks proper quoting, but in this specific instance $DISPLAY and $XAUTHORITY won't contain any shell metacharacter.
The closest to your old rlogin approach would be "ssh -X yourserver.ip.address <x program to run, e.g. meld>" you might need to fiddle with some settings to get it working, however.
On 07/22/2012 12:56 PM, Stephen wrote:
> ssh transfers i think would be the fastest/easiest. there are some gui
> clients that can do this.
>
> On Sun, Jul 22, 2012 at 12:55 PM, Wayne Davis
> <waydavis.phx.lists@gmail.com> wrote:
>> Ok,
>>
>> Years ago, when i worked for frontier global-center, I remember that we
>> could "rlogin" to a system and "Startx". At least I REMEMBER it this way.
>> My recollection was that I was running the GUI LOCALLY and metatdata was
>> being transferred across. VERY fast & efficient screens.
>>
>> A: AM I recalling wrongly?
>> B: I'm wanting to set up a server box on my network for files, music,
>> video that will be headless (No monitor or mouse connected)
>>
>> Running Kubuntu 12.04 as primary OS on all boxes here.
>> I see rlogin, ssh, blah blah blah.......
>>
>>
>> I'm looking for EFFICIENT GUI presentation, File transfers.
>>
>> xvnc11 works but is slow, teamviewer is making connections outside my
>> network to operate AND is wine based :-(
>>
>> What should I use that will keep it S I M P L E (if possible) and secure (
>> I am behind a M0n0wall WRAP firewall) I want to be able to connect at will.
>>
>>
>> Is this going to be a major pain?
>>
>>
>> Thanks everyone for your thoughts :-)
>>
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>
>
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