After having used network-manager on Debian stable (previously, 11, and now, 12) for quite a while, I decided to finally get rid of ifupdown (which has also been installed for quite a while). I uninstalled ifupdown, rebooted the computer, and then purged ifupdown. However, a file has been left over:
Löschen der Konfigurationsdateien von libssl1.1:i386 (1.1.1n-0+deb11u1) ...
Löschen der Konfigurationsdateien von ifupdown (0.8.41) ...
dpkg: Warnung: Während Entfernens von ifupdown ist Verzeichnis »/etc/network/interfaces.d« nicht leer, wird daher nicht gelöscht
which simply means that configuration files of libssl1.1:i386 and ifupdown have been removed and /etc/network/interfaces.d is nonempty and has not been removed. Inside the directory, there's just one file
total 12
drwxr-xr-x 2 root root 4096 Dec 24 2021 .
drwxr-xr-x 7 root root 4096 Jun 12 04:55 ..
-rw-r--r-- 1 root root 67 Jan 13 2021 setup
containing very little:
# cat setup
auto lo
iface lo inet loopback
# auto eth0
# iface eth0 inet dhcp
However, when I try to understand to whom does this file belong to, I get no results:
# dpkg -S interfaces.d/setup
dpkg-query: no path found matching pattern *interfaces.d/setup*
# dpkg -S interfaces.d
dpkg-query: no path found matching pattern *interfaces.d*
Can I remove /etc/interfaces.d/setup or is it still good for anything? If I can remove the file setup, how about the directory /etc/interfaces.d ?
