LightDM can't use the user background on Mate

[Brice Terzaghi]

Using Ubuntu Mate 16.10 (the issue appears too on 16.04 and 17.04 alpha 2).

On Mate, the LightDM Gtk Greeter can't use the user background. It works fine on other DEs like Xfce.

From what I understand, LightDM and/or the Gkt greeter (not sure which one handles the background) gets the background path from Gsettings, so I assume it can't find the one from Mate, which stores it in "org.mate.background picture-filename".

[Brice Terzaghi (terzag)]

I've found additional info in a Cinnamon bug report (https://github.com/linuxmint/Cinnamon/issues/2379). The issue is in fact with mate-settings-daemon (I've updated the current report to ubuntu-mate, not sure it's the right project).

On environments like Gnome 3 / Unity (and presumably Xfce), the settings daemon checks for the use background changes and updates the /var/lib/AccountsSerice/users/username (where "username" is the current user) to add/update the Background option in the [User] section (Background=/path/to/the/background/picture).

It seems to be made through gsettings with a command like this (on Gnome 3):
gsettings set org.gnome.settings-daemon.plugins.background active true

Mate-settings-daemon doesn't seem to have an equivalent to this org.gnome.settings-daemon.plugins.background as I can't find a similar key in org.mate.

Not sure of the proper way to integrate mate-settings-daemon to AccountsService so that it updates the /var/lib/AccountsService/users/username file but I guess it has to work the same way as gnome-settings-daemon and unity-settings-daemon.

[NormMiller (norm)]

On my system, With Ubuntu 16.04 17.10 and Mint 18.2 (all running MATE) Change background doesn't work on any of them. (When I click on a background, the highlight moves, but no change to the actual background. (btw. Themes don't change either)

Clues:
1. Works fine from the "Live" installation USB drive.
2. I am sharing /home among all three Linux versions. The three versions live on sda (an SSD drive)
    /home is on sdb (my system hard drive)
Speculation: Might be "split" system causing the trouble.

[Brice Terzaghi (terzag)]

I don't think this is related to the bug report, unless you're talking about the LightDM (login screen) background, but from your description, I understand that you can't change your desktop background at all. Is that correct?

If that's the case and given that themes don't seem to work either, my best guess would be that mate-settings-daemon is not running. Try to run it in a terminal: do background and theme switch work (while the terminal is open)?

In any case, it's not a good idea at all to have a common home folder for the three distros, especially as they have different versions of MATE. The user's desktop settings are kept in the home folder, so you basically have three DE that constantly try to read settings they can't understand and probably update them.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.