I like to take advantage of the UI customization options that Linux offers. I’m currently using Debian 13 “Trixie”. Sometimes you like the default theme, sometimes you don’t.

In any case, I want to tell here two main changes I did to my desktop.

GRUB default image

In my personal opinion, the default GRUB background image for Debian 13 is a bit sad.

Thus, the steps I took for changing it for something more close to my taste were:

1) GRUB has some limitations.

✅ Supported formats

  • PNG (recommended)
  • JPG/JPEG
  • TGA

PNG works best.

Using a wallpaper from a Lenovo Thinkpad fan page, I created a customized image for this background. Using GIMP, I created a 1024x768 PNG image, which would suit almost any display at boot time.

You can check your GRUB resolution with:

# grep GRUB_GFXMODE /etc/default/grub

If not set, GRUB may default to something like 1024x768.

You can explicitly set resolution:

GRUB_GFXMODE=1920x1080
GRUB_GFXPAYLOAD_LINUX=keep

2) Place the image in the right place.

# cp mybackground.png /boot/grub

3) Tell GRUB to Use the Image

Edit:

$ sudo nano /etc/default/grub

Add or modify this line:

GRUB_BACKGROUND="/boot/grub/mybackground.png"

Make sure:

  • The path is correct
  • Quotes are included
  • The file exists

4) Update GRUB

After saving:

$ sudo update-grub

This regenerates:

/boot/grub/grub.cfg

Reboot to test.

5) (Optional) Enable Graphics Mode if Needed

If the background doesn’t appear, ensure graphics mode is enabled:

In /etc/default/grub, verify:

GRUB_TERMINAL=console

If it’s set to serial or something else, the background won’t show.

If needed, comment it out:

#GRUB_TERMINAL=console

Then run:

sudo update-grub

LightDM background image

I’m using Xfce for Debian 13 as my default desktop.

LightDM is the [display manager] in place, so here is where we have to configure the background image for the login page.

However, I noticed that there is a easier and more straightforward way of changing the desktop theme, altogether.

Debian comes with a list of desktop themes, that you can see by doing

$ update-alternatives --list desktop-theme
/usr/share/desktop-base/ceratopsian-theme
/usr/share/desktop-base/emerald-theme
/usr/share/desktop-base/futureprototype-theme
/usr/share/desktop-base/homeworld-theme
/usr/share/desktop-base/joy-inksplat-theme
/usr/share/desktop-base/joy-theme
/usr/share/desktop-base/lines-theme
/usr/share/desktop-base/moonlight-theme
/usr/share/desktop-base/softwaves-theme
/usr/share/desktop-base/spacefun-theme

“Ceratopsian” is the one by default, and that is the one that I don’t like.

You can easily go to the folder and see the different images. When you see another that you like, you can just change the default theme, to be system-wide, by doing:

$ sudo update-alternatives --set desktop-theme /usr/share/desktop-base/futureprototype-theme
update-alternatives: using /usr/share/desktop-base/futureprototype-theme to provide /usr/share/desktop-base/active-theme (desktop-theme) in manual mode

If you fancy the GRUB image that comes with your theme, just undo the changes done in the GRUB section of this post. You’ll get the default image that comes with the selected theme.