TODO: document what patches have been applied to what packages, whether those patches have been submitted upstream, and whether they have been accepted upstream
Starting with v1.10 (available in Ubuntu 14.04 LTS (trusty) and later), lightdm has some basic multiseat support. After v1.11.7 release, lightdm has gained automatic multiseat support (see bug #1190581). Backporting of automatic multiseat patches for 1.10 series was completed in release 1.10.3, which is already available in trusty-updates repository.
IMPORTANT: Xorg server 1.15.1 packages for Ubuntu 14.04 LTS with backported patches from 1.16 are already available in trusty-updates repository, so we've deleted any xorg-server packages from ubuntu-multiseat PPA. Xorg server 1.16 itself will be packaged for Ubuntu 14.04 LTS, too. Users who want to upgrade to Xorg server 1.16 should install packages xserver-*-lts-utopic.
The gdm package in the multiseat PPA includes patches and changes for the following issues:
upstream bug #704581: Add patch to fix automatic/timed login in multiseat context.
PLEASE NOTE: This software was originally designed to provide a Xephyr wrapper to help configuring multiseat with a single multi-head graphics card. It requires Xephyr to be built with --enable-kdrive-evdev option. However, this approach is no longer recommended by Ubuntu Multiseat team ("nested" video driver approach is the recommended one from now on). However, multi-seat-xephyr binary may still be useful for single-GPU multiseat setups based on nested video driver, because it can be executed, with --daemon option, to launch a bare Xorg server on top of which the nested Xorg servers will be launched.
This package was rebuilt for trusty with additional build-dependencies libsystemd-login-dev and libsystemd-daemon-dev, for full systemd-logind integration. This is needed for correct per-seat automounting of removable media (see bug #1319870).
PLEASE NOTE: if it happens that only one seat is mounting removable media in your system, whether the USB port you plug it is assigned to that seat or not, you may also need to boot Ubuntu with systemd as PID 1 (see this page from Martin Pitt's blog for further details).
At the moment, Xubuntu and Lubuntu do not support per-seat automounting of removable media, even when booting with systemd as PID 1 [UPDATE 2014-05-15] Newer tests with latest package updates reveal that per-seat automounting is working for Xubuntu and Lubuntu now.
In Ubuntu, Edubuntu, [UPDATE 2014-05-15] Lubuntu, and Kubuntu, when a storage device is plugged in a given seat, all seats will be notified, but only the right seat will be able to mount it.
In Ubuntu GNOME, [UPDATE 2014-05-15] and Xubuntu, when a removable media is plugged in a given seat, the other seats won't be notified.