how to set default session in Ubuntu 14.04 LTS?

Solution 1:

Ok after some searching in config files , it did mentioned in /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf

open your terminal with ALT+CTRL+T and type as

sudo nano /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf

and change line user-session to what session you want with session name as mentioned in /usr/share/xsessions/ with

ls /usr/share/xsessions/