Due to following some guy's answer, now when I tried to log into the ubuntu, I was given an ugly blue login window:
I thought I can get rid of it by setting automatic login and found some hints on it, but the "unlock" button in the User Account is greyed so I can not set Automatic Login to "ON", as shown by this picture:
So what should I do to remove the ugly blue log in? Thanks a lot.
A follow-up: I used command "sudo gnome-control-center user-accounts" to turn on the Automatic Login option and restart. But still see the ugly blue login window.
Best Answer
That looks like lxdm, the display manager LXDE uses. I gathered from the comments that you installed LXDE, and because of that lxdm was installed as well. To reset the display manager back to lightDM (Ubuntu's default) you can run this command:
Select "ok" and then "lightdm". Reboot.
Alternatively removing lxdm would probably work too (I haven't tested this though):
Reboot.