How to change lightdm background in bullseye? (additional: weird stat behaviour)

["Christoph K." <christoph@kobenetz.de>]

Hello,


Part 1: lightdm background

I've just upgraded to bullseye and would like to change the background of
the lightdm greeter.

According to ...
https://wiki.debian.org/LightDM#Change_the_greeter.27s_background
... I'm supposed to edit ...
/etc/lightdm/lightdm-gtk-greeter.conf

... which I've done ...

[greeter]
background=/usr/share/xfce4/backdrops/foo.png
user-background=/usr/share/xfce4/backdrops/foo.png

... with no success. Background sticks to dark blue image with debian
artwork.

Before, I had already tried to get a language selector in lightdm by
changing the indicators:

indicators=~host;~spacer;~session;~language;ally;~clock;~power

But lightdm doesn't show a language selector.

I'm suspecting my changes in lightdm-gtk-greeter.conf have no effect.


Question 1:
How do I properly change the lightdm background image?


Question 2:
Is lightdm-gtk-greeter.conf the right place to configure the lightdm
greeter in bullseye?

----

Part 2: weird stat behaviour (ext4 filesystem)

I'm not too familiar with stat and access times, although I do believe to
have some understanding of it. But the following confuses me:

The question related to lightdm was: Is the file
/etc/lightdm/lightdm-gtk-greeter.conf
actually read by lightdm?
To find out I edited the file and restartet lightdm. "stat" didn't show
any access to the file so I did a system reboot because I suspected the
missing access change was due to caching.

But after the reboot the file still had the old access time!
(I removed addional output of the stat command):

/etc/lightdm$ date
Do 16. Jun 11:11:05 CEST 2022
/etc/lightdm$ stat lightdm-gtk-greeter.conf 
 Datei: lightdm-gtk-greeter.conf
Zugriff:     2022-06-16 10:43:18.769291459 +0200

FYI: "Zugriff" is access time in german

Reboot was at 10:45,
access time is 10:43.

Is it correct to conclude that the file has not been read during bootup?
Or am I overlooking something?


To further elaborate I did another test on a test.txt file.
Procedure:
1. touch test.txt
2. stat test.txt -> correct access time from touch
3. cat test.txt
4. stat test.txt -> access time changed due to cat - fine
5. cat test.txt
6. stat test.txt -> still the same access time as in step 4 - caching?
7. reboot
8. cat test.txt
9. stat test.txt -> STILL the same access time as in step 4 - WTF?

Expectations:
1) After a reboot there is no cache to read from.
2) The cat command accesses the file.
3) Stat shows the time of "cat" in the access time stamp.

But 3) does not happen. More precisely: It only happens sometimes.


Question 3:
Could someone please explain to me what's going on here with stat?


Thanks,
Christoph