I run a number of computer labs, and use lightdm with the gtk greeter.
I haven't had time to patch the code, but have looked through the code.
Despite being able to configure a default session for ligthdm, once
lightdm has entered and exited a session it stores that selection in
its XDG_CACHE_HOME directory. It then uses that saved session as the
default for the next time, overriding the default preference.
I can see where this might be an ok behavior in a home environment, but
in a lab environment it is problematic because users tend to expect the
same defaults every time rather than based on the last user.
(I've temporarily disabled this by making a link to /dev/null from
$XDG_CACHE_HOME/lightdm-gtk-greeter, preventing lightdm-gtk-greeter
from creating its state file.)
-- System Information:
Debian Release: 8.5
APT prefers stable
APT policy: (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 3.16.0-4-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: systemd (via /run/systemd/system)
Versions of packages lightdm-gtk-greeter depends on:
ii libc6 2.19-18+deb8u4
ii libcairo2 1.14.0-2.1+deb8u1
ii libgdk-pixbuf2.0-0 2.31.1-2+deb8u5
ii libglib2.0-0 2.42.1-1+b1
ii libgtk-3-0 3.14.5-1+deb8u1
ii liblightdm-gobject-1-0 1.10.3-3
ii libx11-6 2:1.6.2-3
Versions of packages lightdm-gtk-greeter recommends:
ii desktop-base 8.0.2
ii gnome-icon-theme-symbolic 3.12.0-1
ii gnome-themes-standard 126.96.36.199-1
ii policykit-1 0.105-8
lightdm-gtk-greeter suggests no packages.
-- Configuration Files:
/etc/lightdm/lightdm-gtk-greeter.conf changed [not included]