lightdm is writing config files to /

[kurumushi]

Describe the bug

On a fresh install, lightdm is writing several files to /
These should probably be either in /root or in some other runtime directory.config .cache and .gtkrc-2.0

[kris@kris:~]$ ls -la /
total 4
drwxr-xr-x   1 root root  144 Aug 23 14:59 .
drwxr-xr-x   1 root root  144 Aug 23 14:59 ..
drwxr-xr-x   1 root root    4 Aug 23 14:58 bin
drwxr-xr-x   1 root root   78 Aug 23 14:51 boot
drwxr-xr-x   1 root root   80 Aug 23 14:59 .cache
drwxr-xr-x   1 root root   44 Aug 23 14:59 .config
drwxr-xr-x  20 root root 4100 Aug 23 14:58 dev
drwxr-xr-x   1 root root 1162 Aug 23 14:58 etc
-rw-r--r--   1 root root  438 Aug 23 14:59 .gtkrc-2.0
drwxr-xr-x   1 root root    8 Aug 23 14:51 home
drwxr-xr-x   1 root root   94 Aug 19 13:41 mnt
drwxr-xr-x   1 root root   16 Aug 23 14:37 nix
dr-xr-xr-x 359 root root    0 Aug 23 14:58 proc
drwx------   1 root root  106 Aug 23 15:00 root
drwxr-xr-x  23 root root  640 Aug 23 15:03 run
drwxr-xr-x   1 root root    0 Aug 23 14:51 srv
dr-xr-xr-x  13 root root    0 Aug 23 14:58 sys
drwxrwxrwt   1 root root 1414 Aug 23 15:01 tmp
drwxr-xr-x   1 root root    6 Aug 23 14:51 usr
drwxr-xr-x   1 root root   82 Aug 23 14:58 var

Steps To Reproduce

Steps to reproduce the behavior:

1. Install NixOS with X enabled, using the default lightdm display manager.
2. As soon as the display manager starts, files are written to /

Expected behavior

That my / will stay clean.

Additional context

If I stop display-manager.service, delete the files, then restart it, the files return.

Looking in my /etc/passwd, shows that lightdm does have a home directory set at /var/lib/lightdm. But for some reason these files are not being written there as they should be.

Notify maintainers

@davidak
@bobby285271

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[kris@kris:~]$ nix-shell -p nix-info --run "nix-info -m"
these paths will be fetched (0.06 MiB download, 0.30 MiB unpacked):
  /nix/store/qz0niwvp5q62zf8mrqg277ajmc66haa2-bash-interactive-5.1-p8-dev
copying path '/nix/store/qz0niwvp5q62zf8mrqg277ajmc66haa2-bash-interactive-5.1-p8-dev' from 'https://cache.nixos.org'...
 - system: `"x86_64-linux"`
 - host os: `Linux 5.10.110, NixOS, 21.11 (Porcupine)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.16`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[kurumushi]

I just realized after I posted this that I used an old iso from 21.11 to install. So I reinstalled with 22.05, and this still happens

 - system: `"x86_64-linux"`
 - host os: `Linux 5.15.60, NixOS, 22.05 (Quokka), 22.05.2609.52527082ea2`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.8.1`
 - channels(root): `"nixos-22.05.2609.52527082ea2"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[bobby285271]

Are you using KDE Plasma? Can you reproduce the issue with SDDM?

[kurumushi]

I am using KDE. The issue also happens with SDDM. I went ahead and tested GDM as well (while still using plasma,) and it does not happen.

[bobby285271]

I can reproduce. For my case, in /.cache I saw one single file with ksycoca5_ prefix, after some search it is likely cache for kbuildsycoca5 (libsForQt5.kservice). I have no idea what that package does so far though.

[kurumushi]

All the files in my / are exactly the files being generated in desktop-managers/plasma5.nix

[azahi]

I can reproduce this with Plasma 5/SDDM on nixpkgs-unstable.

[Yarny0]

I also observed these files, tracked down the problem and prepared a pull-request that -- hopefully -- fixes the issue: #199881 . I came to the conclusion that it is best to entirely remove the code that creates those file. However, I feel a bit unconfident about my solution, so it would be good to have it tested by more users. If you can spare the time, please have a look at my draft pull request, maybe try my solution, and feel free to report back or even drop a review. Thanks a lot!