I've upgraded from dual-booting Ubuntu 12.04 LTS / Windows 7 to dual-booting Ubuntu 14.04 LTS / Windows 7.
Before the upgrade, when booting Ubuntu, the login window would appear as expected, waiting for my password. But after upgrading, the login window appears for less than 1 sec (on a solid purple background with a grid of dots) before getting "covered over" by a multicolored wallpaper that says "14.04 LTS" in the lower left corner.
From this point I can get to the desktop either by entering my password "blindly" (with invisible login window), or I can make the login window visible again by moving the mouse a few inches to the right. (The mouse pointer behaves as though it's initially off the left edge of the screen.)
Q: What can I do to prevent the login window from getting hidden in the first place?
UPDATE: In case this might be relevant ...
dir /etc/lightdm -->
lightdm.conf lightdm.conf~ lightdm-gtk-greeter.conf lightdm-gtk-greeter-ubuntu.conf users.conf
cat /etc/lightdm/lightdm.conf -->
[SeatDefaults] greeter-session = unity-greeter user-session = ubuntu allow-guest = false
Per the answer by Xieerqi, replacing
greeter-session = unity-greeter with
greeter-session = lightdm-gtk-greeter is a viable workaround, but does not solve the issue with
unity-greeter. Since one of the links in that answer refers to
lightdm-unity-greeter (i.e., with the prefix
lightdm-), I also tried the line
greeter-session = lightdm-unity-greeter, without success.