Before you mark the question as a duplicate, I read all of the posts regarding this, but nothing helped me. I'd like to change the background picture of the lock screen.

I changed the ubuntu.css and gdm3.css accordingly to

#lockDialogGroup {
  background: #000000 url(file:///usr/share/wallpapers/minimalistic-gray_00323985.jpg);
  background-repeat: no-repeat;
  background-size: cover;
  background-position: center;

Which results in a change of the Background of the log in screen, not the lock screen. When I press super + L the screen containing time has the correct background. When I swipe it up to tipe in my password, the purple Ubuntu screen still appears. If I click to change the user, the log in screen appears with the right background. I have the same background picture enabled in gnome tweaks for desktop background and lock screen.

I'm running Ubuntu 18.04 GNOME on a TuXedo Laptop. And I use Communitheme - maybe thats the problem?

Any ideas why it doesn't work? (I rebooted multiple times, so that's not the problem.)

EDIT: The output of sudo nano /usr/share/gnome-shell/modes/ubuntu.json is

    "parentMode": "user",
    "stylesheetName": "ubuntu.css",
    "enabledExtensions": ["[email protected]", "[email protected]"]
  • @PRATAP Exactly, thats the picture I want to use. Hm, I can change the appearance of the background and lock screen both in settings and gnome-tweaks. I'm not a 100 percent sure, how it's called on your system since mine is in german, but it should be something like Appearance in gnome-tweaks.
    – j3ypi
    Commented Dec 9, 2018 at 12:54
  • I bought it last week, so I assume it's a fresh install. I changed the file, but unfortunately it changes nothing. Maybe it's because I use Communitheme? Or maybe, because it says I don't have the extension installed to change the Shell theme?
    – j3ypi
    Commented Dec 9, 2018 at 13:10
  • @PRATAP See the updated question above.
    – j3ypi
    Commented Dec 9, 2018 at 14:17
  • while i was trying to solve similar question.. i got a clue why it didn't work.. can you please let me know how did you instaall that Communitheme.. snap install or PPA and APT install?
    – PRATAP
    Commented Mar 5, 2019 at 16:38
  • 1
    snap and apt are two different things.. you can get differences easily by googling.. you can check by opening snap file in the below answer and see the color which is showing at lock screen..
    – PRATAP
    Commented Mar 7, 2019 at 7:32

2 Answers 2


If it's a PPA install

sudo add-apt-repository ppa:communitheme/ppa
sudo apt update
sudo apt install ubuntu-communitheme-session

then this is the file


When it's a snap install

sudo snap install communitheme

this is the file


but this snap file is Read-Only.. read about why this snap file cant be saved like other files. https://askubuntu.com/a/1035241/739431..

short .gif file for APT installed Communitheme unlock-screen change...

  • I did, but it didn't fix the problem. There is no difference in just renaming the file, is there? Why should renaming fix the problem? Thanks for the suggestions anyways. Do you have any more ideas left?
    – j3ypi
    Commented Dec 9, 2018 at 14:31
  • Of course not. I followed your instructions thoroughly. But I don't really see a difference between creating a new file and copy-pasting the content, and just renaming ubuntu.css and change the name within the .json file. But my knowledge is limited.
    – j3ypi
    Commented Dec 9, 2018 at 15:02
  • I did exactly what you proposed to, but it had no effect.
    – j3ypi
    Commented Dec 9, 2018 at 15:18
  • Yes, the folder wallpapers exists in that exact directory. Elsewise, changing ubuntu.css wouldn't have had any effect on my login screen, but it had. I tried the black color with no effect. Seems like changing the json file, isn't the only thing one has to change.
    – j3ypi
    Commented Dec 10, 2018 at 7:57
  • But every time I try to change the content of the json file I get this warning (gedit:3917): WARNING **: 08:58:51.596: Set document metadata failed:
    – j3ypi
    Commented Dec 10, 2018 at 8:00

Just use this Extension to change the lock screen Wallpaper

Link: https://extensions.gnome.org/extension/1476/unlock-dialog-background/

install it and change it to any lock screen image

Working on Pop OS 20.10

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