Cinnamon does not pass user background changes to Lightdm

[imarkskinner]

Lightdm is a very popular display manager and it's disappointing that Cinnamon does not pass user display changes to Lightdm so that the per-user background feature can be used.

Whilst I appreciate that Lightdm is not the default display manager used in Mint it would make Cinnamon more versatile if it respected the API's of such a common display manager (excuse me if this is the wrong terminology). Most modern desktop environments utilise this feature and many still do so even if Lightdm is not its default display manager.

I'm working on tracking down exactly how to get this to work but I'm no developer so it's not easy for me, any help would be appreciated.

[imarkskinner]

I have had help elsewhere on a support forum trying to trace down the cause of this problem, and it is somehow related to a plugin in the gnome-settings-daemon. Running

gsettings set org.gnome.settings-daemon.plugins.background active true

in a terminal allows that user to change the Lightdm background using the standard Cinnamon method but with this plugin disabled, nothing happens to lightdm when changing the background in Cinnamon.

As far as I can tell there is no downside to enabling this plugin.

[clefebvre]

cinnamon no longer uses gnome-settings-daemon..

[imarkskinner]

So does this mean, as of Mint 16 Cinnamon will pass wallpaper changes to Lightdm without this plugin, or is this another way of saying "Were not interested in working on this"

Don't misunderstand that as a snide remark, it's your choice either way and obviously Cinnamon is a Mint team project but I think It would be a good way to make Cinnamon more appealing to many other distros.

[dalcde]

I guess it means that your solution works, but since Cinnamon has switched to cinnamon-settings-daemon, it should be

gsettings set org.cinnamon.settings-daemon.plugins.background active true

[imarkskinner]

cinnamon-settings-daemon doesn't include this plugin, can it be forked to cinnamon, without this cinnamon cannot properly interact with lightdm and for the reasons I stated in my first post I think Cinnamon would be a better desktop environment if it integrated well with such a popular display manager providing it is not extremely time consuming to do

[jfarthing84]

Not sure why this was closed as it hasn't been resolved. I see it was supposively fixed in f4e6e1a, but in Cinnamon 2.4.5, this code is nowhere to be found.

[mtwebster]

We have gone back to a c-s-d plugin - the AccountsService call is initiated here:: https://github.com/linuxmint/cinnamon-settings-daemon/blob/master/plugins/background/csd-background-manager.c#L142

which goes here: https://github.com/linuxmint/cinnamon-desktop/blob/master/libcinnamon-desktop/gnome-bg.c#L328 to set the background for LightDM

I just checked that the user file in /var/log/AccountsService, and it is indeed being changed when the background is changed. Has LightDM changed how it works - is it still using AccountsService?

[jfarthing84]

Interesting. The wallpaper is not defined at all for my user in /var/lib/AccountsService/users/*.

[mtwebster]

Is there anything logged in ~/.xsession-errors when switching backgrounds? I'm not sure if AccountsService keeps a log file.

What distro are you on?

[jfarthing84]

Ahh, here we go:

(cinnamon-settings-daemon:4203): CinnamonDesktop-WARNING **: Failed to set the background '/usr/share/backgrounds/luna-wallpapers/Horseshoe Bend Sunset.jpg': GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such method 'SetBackgroundFile'

I'm on Arch.

[mtwebster]

That's why - Arch

SetBackgroundFile is an Ubuntu invention, it's not in vanilla AccountsService.

[jfarthing84]

So, how do we get it working in Arch?

[mtwebster]

Well, I'm not sure we do - there are file ownership issues at play here. It'd be nice for the method to be added to AccountsService upstream, but I'm not sure how receptive they might be to that.

[mtwebster]

https://bugs.freedesktop.org/show_bug.cgi?id=43578

[jfarthing84]

From 2011. Looks like they're not interested.

[mtwebster]

If I get time I'll prepare a patch for AccountsService to add what Ubuntu does... I wouldn't hold my breath though - they're pretty apathetic usually, unfortunately.

[jfarthing84]

I assume there's no API in AccountsService to set an arbitrary value in /var/lib/AccountsService/users/* so you could manually set the background key?

[mtwebster]

Unfortunately no, it's pretty strict.

[jfarthing84]

FWIW, I manually set the Background key in my user's AccountsService key file and it still didn't work. So, there may well be some lightm-gtk-greeter issues in Arch with this as well.