[BUG] Login window: Draw user backgrounds does not work, but it does with system wallpapers.

 * Cinnamon 5.4.9
 * Distribution - Mint 21

Issue

The user's custom wallpapers are not displayed in the login window, only the system ones.

Steps To Reproduce

1. Set as wallpaper any image that is not inside the Linux Mint or Vanessa folders (Background Settings)
2. Then log out or restart your computer.
3. You will notice that the Login Window has not saved your wallpaper and will display the default one.

Expected Behaviour

The login window draws any wallpaper and not just the system ones.

[mtwebster]

Where do you keep the custom wallpaper? Do you have an encrypted home folder? The greeter can't access anything in an encrypted home.

I add a custom folder location in Background Settings (/home/soonan/Pictures/Wallpapers). No, I don't have an encrypted home folder. I would like to know if it is a problem with LightDM or Cinnamon, because I can't find anything similar in their Issues Tab https://github.com/canonical/lightdm/issues. Tell me can you reproduce it? Thanks for your reply.

[mtwebster]

They work fine for me - look at the file /var/lib/AccountsService/users/<your-user-name> - you'll need to be root to do this (type sudo su and you'll end up with a # prompt).j

It should contain something like this:

[org.freedesktop.DisplayManager.AccountsService]
BackgroundFile=<path  to current wallpaper>

[User]
Language=en_US
Session=
FormatsLocale=en_US.UTF-8
XSession=cinnamon
Icon=/var/lib/AccountsService/icons/mtwebster
SystemAccount=false

See if that BackgroundFile field there, and what file it's using. AccountsService is what lightdm uses to get your user info for display in the greeter. When you set a new background in Cinnamon, this should also be getting updated with the new path.

It won't solve your problem, but you could just go ahead and set a path in that file (it won't harm anything).

Make sure you exit out of root when you're done (the normal prompt will return).

Hi, I did different tests with LightDM but it insists on reading only images that are in the / folder any that are in /home will not do it. I can't find what causes this in Mint 21 (and not 20.04 based versions...) Maybe it's an Upstream Bug. So far the only solution has been to move my Wallpapers folder to /usr/share/backgrounds. I'm attaching my logs in case it helps.

/var/lib/AccountsService/users/soonan

[org.freedesktop.DisplayManager.AccountsService]
BackgroundFile='/usr/share/backgrounds/Wallpapers/eberhard-grossgasteiger-8hRtEc9npUg-unsplash.jpg'

[User]
Session=
XSession=cinnamon
Icon=/var/lib/AccountsService/icons/soonan
SystemAccount=false

/etc/lightdm/lightdm-gtk-greeter.conf.d/99_linuxmint.conf

[greeter]
background=/usr/share/backgrounds/linuxmint/default_background.jpg
theme-name=Mint-X
icon-theme-name=Mint-X
font-name=Ubuntu 11
xft-antialias=true
xft-dpi=96
xft-hintstyle=hintslight
xft-rgba=rgb
indicators=~host;~spacer;~clock;~spacer;~session;~a11y;~language;~power
keyboard=onboard
reader=orca
position = 50%,center 50%,center
default-user-image = #avatar-default
screensaver-timeout = 60
a11y-states=contrast;font;keyboard;reader
user-background = false
clock-format = %a %d %b, %H:%M

In /etc/lightdm/lightdm-gtk-greeter.conf.d/99_linuxmint.conf I added the line draw-user-backgrounds=true but it didn't work for me either.

I did this on my current installation and another using VirtualBox without installing anything other than system updates. Not working on both.

[LinuxOnTheDesktop]

Possibly the problem here - with wallpapers somewhere within /home not been previewed in the greeter - owes to permissions. I think that permissions on the wallpaper file, and perhaps its directory, and perhaps the whole directory chain, need to be a particular way. But . . what way? I don't know! On all this, see this issue.

[smurphos]

The problem is permissions - in the file and its parent directory tree has to be world readable to access and draw the background. /home/ and it's default subfolders are not world readable on a new install of 21 (I've only got an updated beta install to look at currently) which differs from Mint 20.x fresh installs.

Fixing that fixes the issue, albeit the new apparent default is better from a user security point of view.

[github-actions]

This issue has been automatically marked as stale because it has not had
any activity in over 2 years.

If this issue is still relevant:

• Please test on a current version of this package.
• Add a comment with your findings

If no activity occurs in the next 30 days, this issue will be
automatically closed. Issues can be reopened if needed.

[github-actions]

This issue has been automatically closed due to inactivity.

If you can still reproduce this issue on a current version,
please feel free to reopen it with updated information.

[WhosyVox]

This bug is still relevant but applies to systems installed (or users created?) only since Linux Mint 21.

Prior to this, user home directories has the 755 (rwxr-xr-x) permissions set, so that the LightDM user could read user files to draw the background.

As of Mint 21 (I guess as a change to Ubuntu), this changed to 700 (rwx------) — limiting the scope of this feature to work only on system wallpapers or those the user has placed outside of their home.

Users on older installs (like myself) are unaffected, which is why I believe you couldn't initially replicate this @mtwebster

---

There are a few viable solutions that I can think of.

One is to simply keep a copy of the user's primary chosen background on the root filesystem: this would ensure the feature works even if the home is encrypted, is on another filesystem that isn't automatically mounted, etc. With the downside that it is going to leave that file exposed outside of their home.

There are also odd choices like copying each user's wallpaper to somewhere in /run at startup, or adding lightdm read access via ACL (though I don't personally like either idea).

I think the copy with a confirmation or a checkbox might be an okay choice. It'd add more code complexity (needing to copy as root for a start), but has the advantages of being:

• optional
• transparent and explicit
• disabled by default

e.g. "Allow on Login screen" [ x ] (Other users will be able to view it)

If selected, any user-chosen background outside of /usr/share/wallpapers will be copied to (say) /usr/share/wallpapers/user/$name and set as their wallpaper.