[systemd-devel] loginctl - multi-seats

Laércio de Sousa laerciosousa at sme-mogidascruzes.sp.gov.br
Mon Aug 25 09:26:01 PDT 2014

I've just started following this discussion (so I don't know if it my reply
will be correctly chained), and I would like to make some comments:

* Starting with version 1.16, Xorg server no longer handles VTs if it was
started as a non-seat0 X server i.e., if -seat option with a non-seat0
value was passed. So there's no need to pass option -sharevts or using
systemd-multi-seat-x wrapper with this version.

* Moreover, a new xorg.conf entry called "MatchSeat" was introduced in
version 1.16. It allows configuring multiseat even if you're using non-KMS
video drivers. For example, with you have a NVIDIA graphics card with
binary driver, you can configure a secondary seat with the following

Section "Device"
Identifier "card0"
Driver "nvidia"
MatchSeat "seat-1"

provided you tag another suitable device (e.g. a USB hub) as
"master-of-seat" and attach it to "seat-1".

About configuring multiseat using a single multi-head graphics card, the
only current available way to do this is with nested X servers:

1. Start a bare X server properly configured to span all available
monitors. It should be already running when your display manager service

2. On top of this host X server, start a nested X server for each seat. The
nested X server window geometry (size & position) should be calculated to
fit a given monitor. Currently there are two options for nested X servers:
    * Xephyr (must be built with option --enable-kdrive-evdev, supports
input device coldplugging only)
    * Xorg + xf86-video-nested driver (early development, best option for

Next Xephyr release (1.17) will have support to a special "-output NAME"
option which will make it fit a given output monitor. Desired NAME value
can be obtained by running "xrandr -display <HOSTX-DISPLAY> -q".

I'm already using this scheme to set up a 3-seat system (1 integrated Intel
graphics device for seat0 + 1 Silicon Motion SM501 dual-head PCI graphics
card for the other seats). Since nested X servers don't touch VTs, I'm
afraid of using such X servers with seat0.

*Laércio de Sousa*
*Orientador de Informática*
*Escola Municipal "Professor Eulálio Gruppi"*
*Rua Ismael da Silva Mello, 559, Mogi Moderno*
*Mogi das Cruzes - SPCEP 08717-390*
Telefone: (11) 4726-8313
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