I just installed Ubuntu 18.04 and I wanted to change lock/login screen background. I have 2 screens with different resolution and I want to have the same picture on both of them. I changed regular wallpaper and lock screen via system settings, But when I lock the computer and the I want to unlock it, the login screen has just default purple color as background. I tried to set it up by changing /usr/share/gnome-shell/theme/ubuntu.css, but I don't know which parameters and values to use, because whatever I try, the result is messed up every time (screen) - wallpaper is being cut randomly etc.

I have lockDialogGroup set like this right now

#lockDialogGroup {
  background: #2c001e
  background-repeat: repeat;
  background-size: cover;
  background-position: center;

This is how the login screen looks right now

  • yes it is correct, I can see the walllpaper that I set up, but it's always somehow shifted, stretched or there is edge between repeated picture (as one edge is somewhere in the middle of the screen and the picture is repeated so you can see it continuing)
    – Tomica
    Dec 10, 2018 at 17:36
  • I highly doubt that this will help with scaling and positioning of the wallpaper... I will edit the post and add photo of it
    – Tomica
    Dec 10, 2018 at 17:46
  • I wonder if this info is helpful to you? Quoting: gdm3 reads /etc/gdm3/custom.conf for its configuration. For each local display, gdm starts an X server and runs a minimal GNOME session including a graphical greeter. If configured so, the main gdm process also listens for XDMCP requests from remote displays. These requests can either be direct, causing gdm3 to start a session on the remote display, or indirect, causing a chooser to be opened.
    – Sun Bear
    Aug 15, 2019 at 14:20

2 Answers 2


I figured out a way to extend wallpaper with 2 displays, by changing /usr/share/gnome-shell/theme/ubuntu.css as follow:

#lockDialogGroup {
  background: #2c001e
  background-repeat: repeat;
  background-size: 1920px 1080px;
  background-position: 0 0; }

In my case, both of my display is 1080p.


OK, I solved it with a little workaround... Just edited the wallpaper in gimp (created 1 large picture so when it's spread across both screens, it fits)

enter image description here


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