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If I switch user in a terminal.

su bob

I can't open gedit because bob doesn't own the display.

If I execute

xhost +

before switching to bob I can open the display for some applications but not all. I get the following output when trying to execute gedit:

(crashreporter:4415): GnomeUI-WARNING *: While connecting to session manager: None of the authentication protocols specified are supported.
GLib-GIO:ERROR:/build/buildd/glib2.0-2.28.6/./gio/gdbusconnection.c:2279:initable_init: assertion failed: (connection->initialization_error == NULL)

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Try command line editors like nano. –  Oxwivi Jun 28 '11 at 13:08
@Oxwivi Sure, and I do use nano a lot but in this case gedit is just one of the GUI applications I wasn't able to open. –  z7sg Jun 28 '11 at 13:30
The only program you can't open as another user? You should include it in the question. –  Oxwivi Jun 28 '11 at 13:38
Try to avoid xhost + if you're on a networked computer, as that disables X security and gives anyone on the network permission to connect to your X display and do things like reading your keyboard from remote... –  Riccardo Murri Jun 28 '11 at 13:46
@Oxwivi It could also be firefox, that doesn't work either, it's just in general, I want to be able to do this. gedit was a poor example, you are right about that. –  z7sg Jun 28 '11 at 13:50

2 Answers 2

up vote 3 down vote accepted

If you want to allow user bob to access your existing X session from the command line, you can enter these commands at the terminal prompt:

xauth nextract - $DISPLAY | sudo -u bob xauth nmerge -

Thius uses the xauth command to extract the authentication information for the current user (first part of the command, before the |) and then merge it into user bob's $HOME/.Xauthority file. Note that it requires /etc/sudoers to be configured so that you are allowed to run commands as user bob (this is the default if you're the admin user on a Ubuntu box).

You can then switch to user bob with su -l.

Alternatively, you can issue these separate commands:

xauth nextract - $DISPLAY > /tmp/xauth.temporary.file
su -l bob -c 'xauth nmerge - < /tmp/xauth.temporary.file'
rm /tmp/xauth.temporary.file

Note that:

1) the temporary file must have permissions such that user bob can read it (which often means that any user on the system can read it);

2) there is a time window during which any user that can read the temporary file can get access to your X display.

Therefore, it is better to use the sudo approach as it does not have these downsides.

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I got this to work, but: su: must be run from a terminal –  z7sg Jun 28 '11 at 13:34
@z7sg: Yes, of course it must be run in a terminal. Isn't that what your question is about? How to switch to another user in a terminal and still be able to launch X applications from that same terminal? –  Riccardo Murri Jun 28 '11 at 13:44
@Ricardo Yes, but su doesn't like being run from a pipe. It's a security issue. –  z7sg Jun 28 '11 at 13:47
@z7sg Oh, I see. You're right, but you can use sudo instead of su and not run into this problem. I'll edit my answer with details. –  Riccardo Murri Jun 28 '11 at 14:03
From my desktop running xubuntu, I run ssh -X otherhost. From that host, DISPLAY is "localhost:10.0". When I try xauth extract - $DISPLAY I get an error, No matches found, authority file "-" not written –  djb Nov 26 '13 at 20:25

Another way, after xhost + has been executed:

dbus-launch gedit --sm-client-disable
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