I have just upgraded from Ubuntu 12.04.4 LTS to 14.04 LTS on an i386 system (Dell Optiplex 740, with an integrated nvidia quadro NVS 210S chipset).
The upgrade proceeded smoothly without any problem.
In 12.04 I had the possibility of enabling the 2D Unity shell (or gnome-classic shells, and other alternatives) from the main log in screen.
However, after upgrading to 14.04 I see no way to specify my default log in session (there is no icon available to open a menu in the log in screen).
How can I enable alternative sessions in 14.04?