Fri, 19 Dec 2014
Multiseat LightDM
After getting a new mainboard, I have upgraded my home computer to Fedora 20, and made my multiseat setup use the udev/logind/loginctl seat tags. About a month ago I have discovered that the seat numbers are not correctly assigned to sessions by xdm(8), so I started to look for solutions. Of course, that piece of crap called gdm was not even been considered for obvious reasons. Apparently the solution does exist, and suprisingly enough, it is really nice: it is called LightDM.
LightDM is the display manager. It has cleanly separated the display manager part (starting up the X servers, listening on XDMCP, etc.), and the user interface part (chooser). The later can be selected from various options - e.g. a KDE/Qt compatible one, and a GTK+ compatible one. The configuration is pretty straigthforward, and it does not try to hide anything from the user, unlike the above mentioned piece of crap.
The multiseat setup in LightDM is pretty straightforward: in /etc/ligthdm/lightdm.conf I have to add the following:
[Seat:0] xdg-seat=seat0 xserver-command=X -layout Primary -isolateDevice PCI:0:2:0 -seat seat0 vt7 [Seat:1] xdg-seat=seat1 xserver-command=X -layout Secondary -isolateDevice PCI:1:0:0 -seat seat1 -sharevts vt7
In the udev tags, I had to tag the following device as belonging to Seat1 (using loginctl(8)):
- The DRM device of the graphics card (.../drm/card1)
- The FB device of the graphics card (.../graphics/fb1)
- The sound card ports (.../sound/card1/inputXX)
- The USB port for the mouse (.../usb5/5-1)
- The USB port for the keyboard (.../usb5/5-2)
And that's it! The only (minor) nitpick is, that the GTK+ greeter does not remember the last logged-in user per seat, so it preselects the last logged in user on both seats by default. But we usually log in only after the reboot, so it is not a big problem.