Configuration of ligthdm 1.2

The configuration is pretty similar to that of lightdm 1.0. The changes are indicated in red.

/

|

+-/etc

|  |

|  +-/default

|  |  |

|  |  +-multiseat

|  |

|  +-/lightdm

|  |  |

|  |  +-lightdm.conf

|  |

|  +-/X11

|  |  |

|  |  +-xorg.conf

|  |

|  +-/init.d

|  |  |

|  |  +-multiseat

|  |

|  +-/udev

|  |  |

|  |  +-/rules.d

|  |     |

|  |     +-00-multiseat.rules

|  |

|  +-/multiseat

|     |

|     +-multiseat.conf

|     |

|     +-/scripts

|        |

|        +-helper-functions

|        |

|        +-match-and-name

|        |

|        +-multiseat-greeter-1

|        |

|        +-multiseat-greeter-<n>

|        |

|        +-fake-greeter

|        |

|        +-Xephyr-seat-1

|        |

|        +-Xephyr-seat-<n>

| 

+-/usr

    |

    +-/share

       |

       +-/xgreeters

          |

          +-multiseat-greeter-1.desktop
          |
          +-multiseat-greeter-<n>.desktop

          |

          +-xinerama.desktop

The lithdm.conf is different than in lightdm 1.0, because it explicitly specifies a distinct xserver-command for each seat, the same with greeter-session.

The xserver-command for the seat <n> references its corresponding Xephyr-seat-<n> script, which, in turn, has its seat number hardcoded. The greeter-session for the seat <n> references its corresponding multiseat-greeter-<n>.desktop file, which has a hardcoded reference to its corresponding multiseat-greeter-<n>, which in, turn, has its seat number hardcoded.

The /etc/init.d/multiseat is changed now because it has a LSB-style header, making it suitable for a dependency-based boot. To create appropriate symlinks call

$ update-rc.d multiseat defaults

Multiseat setup - multiseat-greeter-1.desktop

[Desktop Entry]
Name=LightDM GTK+ Greeter
Comment=This runs the GTK+ greeter, it should only be run from LightDM
Exec=/etc/multiseat/scripts/multiseat-greeter-1
Type=Application
X-Ubuntu-Gettext-Domain=lightdm

Multiseat setup - multiseat-greeter-1

#!/bin/bash
#
#multiseat wrapper around ligthdm greeter in order to position 1 Xephyr instance
#
. /etc/multiseat/scripts/helper-functions

PRIMARY=`get_conf 0 PRIMARY`
SEAT=1

if [ $SEAT != $PRIMARY ]; then
    XEP=`XAUTHORITY=/var/run/lightdm/root/:0 xwininfo -root -children -display :0 | grep "Xephyr on :$SEAT" --max-count=1`;
    XEPHYR_WIN_ID=`echo ${XEP} | cut -d' ' -f1`;
    DISPLACEMENT=`get_conf $SEAT DISPLACEMENT`
    DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/:0 wmctrl 2>&1 -v -i -r ${XEPHYR_WIN_ID} -e 0,${DISPLACEMENT},-1,-1;
fi

XAUTHORITY=/var/run/lightdm/root/:$SEAT
DISPLAY=:$SEAT
exec /usr/sbin/lightdm-gtk-greeter

Multiseat setup - Xephyr-seat-1

#!/bin/bash
#
# $1 - display number of this Xephyr

. /etc/multiseat/scripts/helper-functions

trap "" usr1

XEPHYR=/root/Xephyr-new
export DISPLAY=:0
export XAUTHORITY=/var/run/lightdm/root/:0

SEAT=1

SIZE=`get_conf $SEAT SIZE`
KEYBOARD=`get_conf $SEAT KEYBOARD`
LAYOUT=`get_conf $SEAT LAYOUT`
MOUSE=`get_conf $SEAT MOUSE`
DPI=`get_conf $SEAT DPI`

exec $XEPHYR -retro -screen ${SIZE} -keybd evdev,,device=/dev/input/${KEYBOARD},xkbrules=evdev,xkbmodel=evdev,xkblayout=${LAYOUT} -mouse evdev,,device=/dev/input/${MOUSE} -dpi ${DPI} $1

Multiseat setup - init.d/multiseat

#!/bin/sh
### BEGIN INIT INFO
# Provides:          multiseat
# Required-Start:    bootlogs
# Required-Stop:
# Default-Start:     1 2 3 4 5
# Default-Stop:
# Short-Description: Trigger udev rules
# Description:       For some reason the rules for multiseat config need to be
#                    fired once more and later than at the very beginning.
### END INIT INFO


/sbin/udevadm trigger

Multiseat setup - lightdm.conf

[LightDM]
greeter-user=root
user-authority-in-system-dir=false
common-vt=true

[SeatDefaults]
xserver-allow-tcp=false
greeter-hide-users=true
user-session=lightdm-xsession
session-wrapper=/etc/X11/Xsession

[Seat:0]
xserver-command=X -br -dpms -s 0 -novtswitch
greeter-session=xinerama

[Seat:1]
xserver-command=/etc/multiseat/scripts/Xephyr-seat-1
greeter-session=multiseat-greeter-1

[Seat:2]
xserver-command=/etc/multiseat/scripts/Xephyr-seat-2
greeter-session=multiseat-greeter-2

lightdm 1.2, debian Wheezy

The time has come and lightdm 1.2 is in Wheezy. There is no way but making it work. The good news is that I did it; I have a working system prepared as a customized Debian Live on a USB stick. The not so good news (but not so terribly bad either) is that the configuration is a little less elegant. However, there are only 2 small patches to lightdm to  make it work. Actually, these are the same as the first 2 patches out of the 4 used in lightdm 1.0.

Here is the story: the 2 patches deal with removing unused lock files from /tmp (their presence influences the choice of the display number in subsequent runs of lightdm) and with adding an option to use the same vt for all X servers. This is the same as with lightdm 1.0. The difference is that the 2 remaining patches have not been applied. They don't apply at all, they are not even close, because the architecture of lightdm changed since 1.0 and the processes are started in a different way while the 2 remaining patches added an option to pass seat numbers to X servers and to greeters; both X servers and greeters are started as new processes. But there is a satisfying workaround: do not even try applying them, the trade-off being a less elegant configuration.

In the lightdm 1.0 solution there is one central multiseat.conf, which is used both by udev to name event interface nodes in /dev/input and by multiseat scripts to associate keyboards/mice with seats and to move X servers into their corresponding positions within one big Xinerama screen. The multiseat scripts were generic, so they needed to be told (in an invocation parameter) which seat they relate to; the solution was also nicely scalable - there was only one file, the multiseat.conf, which needed to be edited to specify the keyboards/mice matching to their seats. In the lightdm 1.2 solution the scripts cannot be told which seat they relate to (because lightdm is not patched to do so, for the reasons explained earlier), so some of them are copied, in as many instances as there are seats, and by their construction they relate to a fixed seat. The good thing is that the patches which have been applied are really simple, so it might be easier to make it to the lightdm mainline.

You can get the changes from here:

bzr branch lp:~andrzejtp2010/lightdm/lightdm-1.2-xephyr-multiseat

bzr diff -r1493 > multiseat.patch

and follow the build instruction from here.

Stay tuned.