both the above answers didn't work for me (Ubuntu x64 15.04).. the Ubuntu wiki for LightDM works for me, so thought to post here for others who are looking for it although they can too follow the wiki..
source: What is LightDM?
as per Ubuntu wiki if we want to override the system configured default session (provided in
/usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf) we should make a file
/etc/lightdm/lightdm.conf.d/50-myconfig.conf and define our stuffs there...
for example i want to disable listing user accounts, enable manual login at greeting or login screen and disable guest so wrote the following in
sudo mkdir /etc/lightdm/lightdm.conf.d/ in terminal to create
lightdm.conf.d folder in
sudo nano /etc/lightdm/lightdm.conf.d/50-myconfig.conf
and put the following lines:
now save the file and restart or logout, this is how i get it working.. :)