Change Ubuntu 20.04 login theme

Question

I want to use Materia theme as my login screen (gdm) theme. I used loginized app for changing the theme, I used it on arch and it worked well. But it is not working for ubuntu 20.04.

Answer 1

from the file /usr/share/themes/Materia/gnome-shell/README.md.. please read the warnings first.. If you wish to proceed even after understanding the warnings in it..

follow the below steps to have a Materia theme for gdm login greeter..

Please note that This is just one of the workaround.. there are different ways..

Install the required package

sudo apt install libglib2.0-dev-bin

Backup the original theme first.

sudo cp -av /usr/share/gnome-shell/gnome-shell-theme.gresource{,~}

Change the Directory to Materia theme

cd /usr/share/themes/Materia/gnome-shell/

Create a copy of gnome-shell.css as gdm3.css

sudo cp gnome-shell.css gdm3.css

Edit the file gnome-shell-theme.gresource.xml to add the line <file>gdm3.css</file>

sudo -H gedit gnome-shell-theme.gresource.xml

Observe, I have add the line <file>gdm3.css</file> under this line <file>gnome-shell.css</file>

<file>extensions/workspaces-to-dock/workspaces-to-dock.css</file>
<file>gnome-shell.css</file>
<file>gdm3.css</file>
<file>icons/eye-not-looking-symbolic.svg</file>
<file>icons/eye-open-negative-filled-symbolic.svg</file>

Save the file & close.

Create the required "gresource" file replacing the original file /usr/share/gnome-shell/gnome-shell-theme.gresource

sudo glib-compile-resources --target=/usr/share/gnome-shell/gnome-shell-theme.gresource gnome-shell-theme.gresource.xml

Ok, Manipulation is done. Now tell the gdm to use the above manipulated file for login screen with below command and choose the number related to file /usr/share/gnome-shell/gnome-shell-theme.gresource.

sudo update-alternatives --config  gdm3-theme.gresource

Example:

admin@i7-4770:~$ sudo update-alternatives --config  gdm3-theme.gresource 
[sudo] password for admin: 
There are 2 choices for the alternative gdm3-theme.gresource (providing /usr/share/gnome-shell/gdm3-theme.gresource).
Selection    Path                                                           Priority   Status
0            /usr/share/gnome-shell/theme/Yaru/gnome-shell-theme.gresource   15        auto mode

1            /usr/share/gnome-shell/gnome-shell-theme.gresource              10        manual mode
2            /usr/share/gnome-shell/theme/Yaru/gnome-shell-theme.gresource   15        manual mode

Press <enter> to keep the current choice[*], or type selection number: 1
admin@i7-4770:~$ 

Reboot to see the changes..

Optinally you may change the background color or image or any part.

If something gnone wrong and not able to see the login screen.. follow the README.md file.

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The above changes only the login screen theme to Materia.. for lock screen you need to configure it separately. Follow this link How to customize Lock Screen theme in Ubuntu 20.04 to understand the concept, Once understood, you may use this content for proper configuration.

{
    "parentMode": "user",
    "stylesheetName": "gnome-shell.css",
    "themeResourceName": "gnome-shell-theme.gresource",
    "debugFlags": ["backtrace-crashes-all"],
    "enabledExtensions": ["ubuntu-dock@ubuntu.com", "ubuntu-appindicators@ubuntu.com", "desktop-icons@csoriano"]
}