I've also seem this warning message and the root.root permissions on /var/lib/lightdm/data/
This system previously had a very minimal (debootstrap'd) Debian Bullseye installation. I then did: # apt-get install openbox lightdm and rebooted. X starts and shows a background image but there are no login controls or anything else. On this first boot, /var/log/lightdm/lightdm.log says: [+0.06s] WARNING: Could not enumerate user data directory /var/lib/lightdm/data: Error opening directory '/var/lib/lightdm/data': No such file or directory Looking at the permissions: # ls -ld /var drwxr-xr-x 12 root root 4096 Oct 11 16:36 /var # ls -ld /var/lib drwxr-xr-x 23 root root 4096 Oct 17 16:34 /var/lib # ls -ld /var/lib/lightdm/ drwxr-x--- 4 lightdm lightdm 4096 Oct 17 16:36 /var/lib/lightdm/ # ls -ld /var/lib/lightdm/data/ drwxr-xr-x 3 root root 4096 Oct 17 16:36 /var/lib/lightdm/data/ # ls -ld /var/lib/lightdm/data/lightdm/ drwxrwx--- 2 lightdm lightdm 4096 Oct 17 16:36 /var/lib/lightdm/data/lightdm/ # ls -l /var/lib/lightdm/data/lightdm/ total 0 Observe the ownership going down the hierarchy is root then lightdm then root then lightdm, which seems peculiar. On the second boot, this warning was not shown - presumably the missing directory was created on the first boot albeit with the surprising ownership. lightdm still didn't work, but that was due to other issues..... Regards, Phil.
