A background image may silently not be displayed if permissions are not just so

[ghost]

slick-greeter 1.0.7
Cinnamon 3.4.6
Mint 18.2
64-bit

Issue

Sometimes a background image (wallpaper) does not appear in the greeter. The problem seems to owe to file and folder permissions - and I've managed to fix the problem in the past. Knowing that permissions are the problem is not trivial, and the same goes, but more so, for fixing the problem.

Steps to reproduce

Unsure. Try fiddling with the permissions of a desktop file. Possibly simple e.g. removing write access from the user concerned, or even from any folder in the hierarchy containing the wallpaper file, would suffice.

Expected behaviour

At best, permissions should cause no problem at all so long as the greeter application - and perhaps the user in question - has read access to the wallpaper file. Failing that, some sort of error message and/or 'fix permissions' button would be good.

[clefebvre]

lightdm-settings should probably test the permissions and/or detect the presence of an encrypted home directory, and in this case prevent you from choosing this background.

[LinuxOnTheDesktop]

I've run into this problem (and not for the first time). I cannot get any image under /home to display in the greeter. The only way I could get a custom background to show was to copy it to a subfolder of /usr/share/backgrounds and also to set its permissions to rw-r-r. Also, getting that subfolder to show up in the wallpaper picker was no fun - and, of course, having a user image outside that user's home folder is not right.

I am not using encryption.

Please, at the least, specify somewhere just what permissions are needed for: the image file itself; its containing folder; any other entity that needs permissions to be just so. Also, if some locations for the image file will cause problems, then what are those locations and why do they cause problems, please? (I understand that encrypted locations will be a problem - but are there any other locations / facts about locations that can cause problems?)

Quite a few users have run into this problem over the years, as one can tell from the Mint forum (well, when the forum is not down, which it is at the moment).

[LinuxOnTheDesktop]

Cf. this Nemo bug.

[clefebvre]

I was going to put a warning in the tooltip but I'm not even sure what to write... I mean, so many things could go wrong here, this is a user error I'm afraid.

• The picture could be wrong (wrong format, wrong data)
• The picture permissions could be wrong
• The containing folder permissions could be wrong
• One of the parent directories of the folder could be wrong (by default your home is 700 afaik, so it's not accessible)
• Permissions could be fine but disk encryption could limit access before you log in

[clefebvre]

Note: Don't select a background from your home directory if it's encrypted or if its permissions are restricted.

Added as a tooltip.