Seen similar question many times on AskUbuntu, but most answers was bout unity-helpers or gconf ...canonical... etc, so this actually doesn't seem to work.
The problem is that I decided to move to lightdm from gdm. Yep, it works,but I can't setup background image to it - always getting black bg color in exchange of picture.
My configs:

tempos@parmasse ~ $ cat /etc/lightdm/lightdm-gtk-greeter.conf 
# logo = Logo file to use, either an image absolute path, or a path relative to the greeter data directory
# background = Background file to use, either an image path or a color (e.g. #772953)
# theme-name = GTK+ theme to use
# icon-theme-name = Icon theme to use
# font-name = Font to use
# xft-antialias = Whether to antialias Xft fonts (true or false)
# xft-dpi = Resolution for Xft in dots per inch (e.g. 96)
# xft-hintstyle = What degree of hinting to use (hintnone, hintslight, hintmedium, or hintfull)
# xft-rgba = Type of subpixel antialiasing (none, rgb, bgr, vrgb or vbgr)
# show-language-selector (true or false)

The file itself:

tempos@parmasse ~ $ ls -la /usr/share/backgrounds/lightdm.jpg
-rwxrwxrwx 1 root root 1362684 авг 14 12:36 /usr/share/backgrounds/lightdm.jpg
  • Does your image file has correct permissions? Try to copy it to the default directory /usr/share/backgrounds/. – dsmsk80 Aug 14 '13 at 12:23
  • @dsumsky As you can see below config, it's already in this directory and has 777 rights – Constantine Kozlov Aug 14 '13 at 12:34

You can try removing alpha channel from your background image (you can do it with gimp).
for check if it have an alpha channel you can do:
file /usr/share/backgrounds/lightdm.jpg

If it have an alpha channel it will show 'RGBA'.
A means Alpha channel.
so without is 'RGB'.

if without not work, you can try adding new one:

convert <input> -alpha on <output>

If you cannot set by configuration file of lightdm because of some strange problem you can do it using feh.

(feh — image viewer and cataloguer)

It have not so many dependence and is good for see image file.

from feh you can set background/wallpaper almost everywhere

feh --bg-fill /usr/share/backgrounds/lightdm.jpg

feh can also be used as a background setter. Unless you pass the --no-fehbg option, it will store the command line necessary to set the background in ~/.fehbg, so to have your background restored every time you start X, you can add "eval $(cat ~/.fehbg)" to your X startup script (like ~/.xinitrc).


Thanks all.
Seems, that it was some bug - in lightdm itself (meening package-specific or some libraries) or, possibly, it was simply installed with some errors/bugs. I'm now trying to install many different things, like compiz, awesome, enlightenment, lightdm and others, so can't be sure.
The fact is today both lightdm and lightdm-gtk-greeter received updates, and this fixed background's problems even with original images and config.


I found a solution :

I picked my preferred wallpaper and copied in the directory provided by aliceinwire.

sudo cp your-wallpaper.jpg /usr/share/backgrounds/lightdm.jpg

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