Kubuntu 12.04: Change login screen background?

Question

I am having trouble changing my login screen background. I can select the default wallpaper, the Kde-default one, but whenever I select my own custom wallpaper, there is no image, just a solid color. Normally, I would just ignore it, but the thing that bugs me is that this is a fresh install of Kubuntu 12.04 64bit, and the OS before this one, the one which I overwrote, had no trouble using the exact same image as the background.

Settings

In the System Settings application, Login Screen settings, Background tab, enable background, Under "Background", selected Picture, under options, selected Position: Scaled. Colors: Single Color. Blending: No Blending.

Solution

Error messages

Try to launch the KDM login manager configuration module from the konsole ( How to launch Configure Kde control module by command line? )

with the command:

kcmshell4 kdm

Can the KDE make a thumbnail from you picture ?

Wrong extension ?

The KDE is looking the image file extension not what is in the file.

Example changing the picture file extension from the jpg to the png.

The Dolphin can't make the thumbnail:

and the KDM can't use the picture with the wrong extension.

Error message:

kcmshell(2652) KBackgroundRenderer::doWallpaper: failed to load wallpaper "/home/user26687/Templates/kubuntu-wallpaper-v1c.png"

File permissions

(If this is a file permission problem as the Dirk Hartzer Waldeck suggests.)

File manager (Dolphin) right click the file > Properties > Permissions tab

If the file is owned by the root you could change the access permissions or the file owner by launching the file manager with the root rights ( https://help.ubuntu.com/community/RootSudo ):

kdesudo dolphin

Another option is to install the kde service menu: http://kde-look.org/content/show.php/Root+Actions+Servicemenu?content=48411 and use it.

Ubuntu community wiki to set/change file permissions: https://help.ubuntu.com/community/FilePermissions .

Comments

[Dirk Hartzer Waldeck]

sounds like a permissions issue, try running system-settings as root: Press ALT+F2 to open the run dialog Enter kdesudo system-settings Change the login screen now and see what happens.

[user26687]

The "kdesudo system-setting" or "kdesudo kcmshell4 kdm" is workaround to the KDE bug: bugs.kde.org/show_bug.cgi?id=255453.

[drdrez]

kdesudo system-settings does not work, it prompts for a password, but nothing else opens nor do I get any errors. kdesudo kcmshell4 kdm worked though. Thanks for that bug link, makes me feel like KDE4 is some alpha piece of software, in which case it shouldn't be used with Kubuntu 12.04 (or earlier)...

[user26687]

Sorry of the typo - it should be "kdesudo systemsettings" not "kdesudo system-settings". The Kubuntu is probably (?) moving from the KDM to the LightDM with the KUbuntu 12.10: lists.ubuntu.com/archives/kubuntu-devel/2012-June/006193.htm‌​l . The lightdm-kde-greeter is available for the 12.04. The LightDM for the KDE developer's blog: sharpley.org.uk

[drdrez]

Wonderful answer! :D Errors When I run kcmshell4 kdm I get the error QImage::scaled: Image is a null image 4 times, but only when I first open it. Switching to another image and applying does not cause the error... Wrong extension ? Nope, dolphin and KDM config can generate a thumbnail just fine. Image is a .jpg file. File permissions This is the reason. The owner and group are both myself, but I set the permissions on it so that it could be read by group and other. After toggling those permissions, each time the background toggles with it, so the issue was file permissions