Re: [gdm-list] Multi-seat issues with GDM 2.16

[Brian Cameron <Brian Cameron Sun COM>]

Alexander:

gdmlogin and gdmgreeter pretty much do the same thing, so it is unusual
for one to crash and the other to work.  When I have seen problems like
this, it is caused because:

- There is some library that gdmgreeter needs that is not available on
  the system.  If you type "ldd /usr/lib/gdmgreeter", and if any of the
  libraries report problems (like they cannot be found), then this is
  obviously a problem.

- If gdmgreeter is crashing for some reason.

Try this.  Using gdmlogin, log into a normal session and set this
environment variable: "DOING_GDM_DEVELOPMENT=1".  Then run gdmgreeter
from a terminal window within the normal user session.

This lets you run a debug version of gdmgreeter.  Some of the features
are turned off, so it is not an exact test of what code is executed when
it is launched via the main GDM daemon.  However, it is a good test to
run.  If gdmgreeter crashes on startup when DOING_GDM_DEVELOPMENT is
set, then it is often easier to track down why.

If this doesn't highlight the problem (and if turning on GDM debug does
not help), then it would likely be necessary to build a debug version of
GDM, add a sleep() statement to gdmgreeter when it starts up, and attach
a debugger to the process to see why things are going awry.

Brian

> I'm experimenting with multi-seat configuration using DisplayLink devices as per
> instructions on their wiki [1].
>
> The displaylink kernel and Xorg drivers compiled and appear to work, the udev
> scripts on the wiki needed slight change to make it work for me and only the
> last part doesn't seem to work.
>
> When the system boots in runlevel 3 I start /usr/sbin/gdm manually and execute
> ./usbseat.sh 2 to start X and gdm login screen on the terminal with ID 2.
>
> The script uses the following commands:
>
> /usr/bin/gdmdynamic -v -t 2 -s 1 -a "$1=/usr/bin/X :$1 -br -audit 0 -nolisten
> tcp -novtswitch -sharevts -config $TMPFILE"
> /usr/bin/gdmdynamic -v -r $1
>
> Where the TMPFILE is a Xorg config file with proper grouping for display, mouse
> and keyboard.
>
> Xorg starts (I've tested it manually too). The mouse pointer is displayed using
> the default theme for my distro (RHEL5.4), there's a blue circle around the
> pointer for a while indicating that stuff is loading.
>
> Then all of this shows only a black screen and the mouse pointer. It doesn't
> show the login screen as one expects.
>
> The pstree output looks ok:
>      ├─gdm-binary───gdm-binary─┬─X
>      │                         └─gdmgreeter
>
> IIRC gdmgreeter is the application that shows the login screen.
>
> The associated Xorg and gdm logs don't indicate any warnings or errors.
>
> Does anyone have an idea how to debug this or why it's not working? I'm using
> 2.16 which is relatively old and multi-seat support is reported to work on older
> versions.
>
> [1] - http://libdlo.freedesktop.org/wiki/MultiSeatTerminal
>
> Thanks,
> Alexander.
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