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Possible Duplicate:
How do I change the wallpaper in LightDM?

How do i change the background of the login screen on 11.10 i have tried Simple-lightDM-Manager and now all i get is a black screen with dots and the logo

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marked as duplicate by fossfreedom, Jorge Castro, James, Takkat, htorque Jan 31 '12 at 23:20

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

up vote 2 down vote accepted

It's in the file /etc/lightdm/unity-greeter.conf. Open it with gksu gedit /etc/lightdm/unity-greeter.conf from a terminal or run dialogue. Set background= to whatever file you would like.

However make sure that file is accessible to all. It can not be in an encrypted home folder or such. The problem you have is most likely due to unity-greeter for some reason can't access the file you chose.

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An easy down and dirty way is to simply replace /usr/share/backgrounds/warty-final-ubuntu.png with the image of your choice

sudo mv /usr/share/backgrounds/warty-final-ubuntu.png /usr/share/backgrounds/warty-final-ubuntu.png.bak
sudo mv new.img /usr/share/backgrounds/warty-final-ubuntu.png
sudo chmod 644 /usr/share/backgrounds/warty-final-ubuntu.png

Ideally it would be a .png, but other images work as well.

The only disadvantage (IMO) of this method is that /usr/share/backgrounds/warty-final-ubuntu.png may get updated with system upgrades.

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What's weird, is that warty-final-ubuntu.png is actually a Jpeg with a PNG extension. Don't believe me? Open it in Gimp, or right-click, go to the Image tab, and look. (The Summary tab names it as PNG, just because of the extension, but the Image tab actually looks at the data, or at least the header.) – JamesTheAwesomeDude Jan 15 '13 at 21:20

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