Strange lock screen on Ubuntu 16.04

Question

I was cleaning my keyboard with my computer suspended. When I turned on the monitor, my lock screen was totally different to what it should be like. I entered my password, and there was an error report for Ubuntu which I okayed. I hoped it was a one-off, but no!

Now when I lock my screen with super+L, my monitor turns off as though it is going into suspend, and when I move the mouse a black screen comes up before my desktop and the same strange lock screen. My computer suspends as you would expect, except that when I resume, I am faced with the strange lock screen.

I had a look to see if there was anything like it and came across a couple of examples. This seems to be the same problem, except when I login my lock screen is normal: What is this second login screen?. I tried the solutions suggested in that thread, but nothing works.

Same problem but I only have one monitor (no solutions to try in this thread): Lock screen is not working Ubuntu 16.04

When I lock the screen from terminal with dm-tool lock it is as expected, quickly going to the lock screen, and my traditional lock screen, until I enter my password, then instead of going straight to my desktop, it goes through the same thing as when I lock it with super+L -- the long suspense and monitor shutting off, followed by the strange lock screen (when I enter the password there I am returned to desktop).

This is the strange lock screen (with my username redacted)

Traditional lock screen:

Please can anyone suggest what I can do to rectify this?!

Also, I know I only have myself to blame, but surely typing any combination of characters in the password field on the lock screen shouldn't be able to change a fundamental thing like this?!

It sounds/looks like I might have pressed the combination ctrl+alt+* which has disabled a lock screen or something. I haven't enough posts to post another link. Google "Xorg 1.11 Vulnerability: Bypass Screen Lockers With A Keyboard Shortcut" and it is the first post that looks/sounds like what I might have done, but my Xorg server is 1.18, so I haven't tried anything suggested in the linked thread there as it is four years old!

Answer 1

This is the gnome-screensaver (at least I had the same problems few months ago).

sudo apt purge gnome-screensaver

should do the trick.

Answer 2

I've had the same situation after my young daughter was playing with my laptop. :)

Try "alt+super+s" combination when you're on your desktop. Or go to: Universal Access > Screen Reader And turn it OFF. After that you should have normal default lock screen.

You had to press alt+super+s during cleaning, when screen was locked. It's also the way to reproduce this problem and to get this ugly lock screen.

Answer 3

1. If you have recently used lightdm-greeter this screen can appear to remove this perform following commands in terminal:

   sudo apt-get purge lightdm-gtk-greeter*
   sudo add-apt-repository --remove ppa:lightdm-gtk-greeter-team/stable
   sudo apt-get update
   

2. Then edit the following file that reads the greeter:

   gksudo gedit /etc/lightdm/lightdm.conf.d/10-ubuntu.conf
   

   Change the line

   greeter-session=lightdm-gtk-greeter
   

   to

   greeter-session=unity-greeter
   

   If the line above does not exist, add it. If the above file/path does not exits (depends on Ubuntu version) try /etc/lightdm/lightdm.conf instead.

3. Then reconfigure both DM and greeter

   sudo dpkg-reconfigure lightdm unity-greeter
   

4. Then reboot.