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Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su -

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On Fri, Jan 01, 2021 at 07:52:40PM +0100, tomas@tuxteam.de wrote:
> On Fri, Jan 01, 2021 at 10:24:44AM -0700, Charles Curley wrote:
> > On Thu, 31 Dec 2020 22:30:34 -0600
> > David Wright <deblis@lionunicorn.co.uk> wrote:
> > 
> > >   $ /bin/su -
> > >   Password:
> > >   ahost ~# xeyes -display :0.0
> > >   Xlib: connection to ":0.0" refused by server
> > >   Xlib: Client is not authorized to connect to Server
> > >   Error: Can't open display: :0.0
> > >   ahost ~# ln -s ~auser/.Xauthority .Xauthority
> > 
> > Bingo! That, rather than copying .Xauthority, gave me a fix.
> 
> Huh? That is strange. I mean: great it worked for you, but I'd
> like to learn what is going on there :-)

What don't you understand?  In order for an X client to run, it needs
two pieces of information: the DISPLAY to talk to, and the authorization
to be allowed to talk.

For the authorization piece, the client looks for an MIT-magic-cookie
in a file named by the XAUTHORITY variable, or if that variable isn't
set, then it looks for the file $HOME/.Xauthority .

By creating this symlink, David has forever tied root's ~/.Xauthority
file to the one in auser's home directory.  Whenever an X client running
as root tries to run, in the absence of the XAUTHORITY variable, it will
look at ~root/.Xauthority which is a symlink to ~auser/.Xauthority which
is presumably on a local file system that root can read.  So the client
can read the MIT-magic-cookie, so it can authenticate itself to the X
server, so it can run.

This will fall on its face if some user other than auser happens to be
the one who started the X session.

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Thread

Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2020-12-31 23:00 +0100
  Re: Bullseye: setting and using $DISPLAY after su - <tomas@tuxteam.de> - 2020-12-31 23:10 +0100
    Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2020-12-31 23:20 +0100
      Re: Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2021-01-01 01:50 +0100
        Re: Bullseye: setting and using $DISPLAY after su - David Wright <deblis@lionunicorn.co.uk> - 2021-01-01 05:40 +0100
          [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2021-01-01 18:50 +0100
            Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - <tomas@tuxteam.de> - 2021-01-01 20:00 +0100
              Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2021-01-01 22:30 +0100
              Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2021-01-04 13:40 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su  - The Wanderer <wanderer@fastmail.fm> - 2021-01-04 13:50 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2021-01-04 14:40 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - <tomas@tuxteam.de> - 2021-01-04 15:50 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - David Wright <deblis@lionunicorn.co.uk> - 2021-01-06 05:40 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2021-01-06 13:40 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - David Wright <deblis@lionunicorn.co.uk> - 2021-01-06 17:30 +0100
                Re: [SOLUTION] Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2021-01-06 19:50 +0100
        Re: Bullseye: setting and using $DISPLAY after su - Greg Wooledge <wooledg@eeg.ccf.org> - 2021-01-04 13:30 +0100
          Re: Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2021-01-04 19:20 +0100
      Re: Bullseye: setting and using $DISPLAY after su - <tomas@tuxteam.de> - 2021-01-01 10:20 +0100
    Re: Bullseye: setting and using $DISPLAY after su - Charles Curley <charlescurley@charlescurley.com> - 2021-01-01 02:00 +0100
  Re: Bullseye: setting and using $DISPLAY after su - Mark Neyhart <Mark.Neyhart@akleg.gov> - 2021-01-01 04:10 +0100

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