et voila, j'avoue ne rien comprendre a ce langage abscons...merci
prof@Pc-gdc:~$ find /usr/share/lightdm/lightdm.conf.d -name '*.conf' -exec bash -c 'echo -e "\n$1\n"; nl -ba "$1"' _ '{}' \;
/usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
1 [SeatDefaults]
2 greeter-session=unity-greeter
/usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
1 [SeatDefaults]
2 # Dump core
3 xserver-command=X -core
/usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
1 [SeatDefaults]
2 user-session=ubuntu
/usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
1 [SeatDefaults]
2 greeter-wrapper=/usr/lib/lightdm/lightdm-greeter-session
/usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
1 [SeatDefaults]
2 guest-wrapper=/usr/lib/lightdm/lightdm-guest-session