UPDATE for Ubuntu 23.04

1. ubuntu-gdm-set-background-23.04 -> has four options just like the previous versions: Image, Color, Gradient Horizontal, Gradient Vertical.
2. ubuntu-gdm-set-background-23.04-transparent -> sets the login-background color transparent so that the background set via gsettings set com.ubuntu.login-screen background-picture-uri is visible. This is the RECOMMENDED way.

Please follow this link for setting login background via gsettings: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1929536

[Test Case]

1. Boot a desktop session
2. Verify that the greeter shows the default aubergine background.
3. Login as the administrator of the machine
4. Install systemd-container
5. Switch to the GDM user: $ sudo machinectl shell gdm@ /bin/bash
6. Apply a different background with the command: $ gsettings set com.ubuntu.login-screen background-picture-uri 'file:///usr/share/backgrounds/warty-final-ubuntu.png'
7. Logout
8. Verify that the greeter now shows the image warty-final-ubuntu.png.

ubuntu-gdm-set-background script (for changing Ubuntu 20.04, 21.04, 21.10, 22.04 & 22.10 GDM Background) HELP

Download the script with one of these commands:

$ wget -q https://raw.githubusercontent.com/PRATAP-KUMAR/ubuntu-gdm-set-background/main/ubuntu-gdm-set-background && chmod +x ubuntu-gdm-set-background
$ curl -fL 'https://raw.githubusercontent.com/PRATAP-KUMAR/ubuntu-gdm-set-background/main/ubuntu-gdm-set-background' -o ubuntu-gdm-set-background && chmod +x ubuntu-gdm-set-background

There are four options

1. background with image
2. background with color
3. background with gradient horizontal ( requires two valid hex color inputs)
4. background with gradient vertical ( requires two valid hex color inputs)

Tip: be ready with valid hex color code in place of below example like #aAbBcC or #dDeEfF. Change them to your preferred hex color codes. You may choose colors from color-hex.com

Example Commands:

1. sudo ./ubuntu-gdm-set-background --image /home/user/backgrounds/image.jpg
2. sudo ./ubuntu-gdm-set-background --color \#aAbBcC
3. sudo ./ubuntu-gdm-set-background --gradient horizontal \#aAbBcC \#dDeEfF
4. sudo ./ubuntu-gdm-set-background --gradient vertical \#aAbBcC \#dDeEfF
5. sudo ./ubuntu-gdm-set-background --reset
6. ./ubuntu-gdm-set-background --help

RESCUE_MODE, Example Commands:

1. sudo ./ubuntu-gdm-set-background --image /home/user/backgrounds/image.jpg rescue
2. sudo ./ubuntu-gdm-set-background --color \#aAbBcC rescue
3. sudo ./ubuntu-gdm-set-background --gradient horizontal \#aAbBcC \#dDeEfF rescue
4. sudo ./ubuntu-gdm-set-background --gradient vertical \#aAbBcC \#dDeEfF rescue

Why RESCUE_MODE? When you try to change the background with some other scripts and then interact with this script, there could be some conflicts. In case you ran other scripts to change the background and then tried this script, and found conflicts, then add 'rescue' to the end of the command as mentioned above.

Please note that for RESCUE_MODE active internet connection is necessary