How to check what files have been customised in /etc?

[Ralf Mardorf]

On Sun, 13 Dec 2020 11:44:33 +0000, Colin Law mentioned drop-in
directories/files.

Those drop-in files are tricky, especially when using a rolling
release, but they could cause the same kind of issues for release model
distros, probably when upgrading to the next release or when using
third party repositories.

A famous example is /etc/security/limits.conf.

You set all your limits in one place by /etc/security/limits.conf, in
my domain e.g. especially "rtprio" and "memlock". Then a
packager/vendor decides to override those settings by a drop-in file.

I like to have all my settings in one file, not in trillions of
different files, since for my taste it's way more well-structured to
have all the settings manageable by one file. However, I've given up and
now in disgust I'm used to drop-in files. But this doesn't solve the
issue at all, since one drop-in file can override the settings of
another drop-in file by lexical order.

The drop-in file approach is a PITA, since you need to take care that
nothings overrides important settings, just by lexical order.

Usually we nowadays tend to name drop-in files starting with a high
number, to most widely ensure that it's the last used file for
configuration. Instead of "foo.conf" it becomes "99-foo.conf". This
isn't absolutely secure, IOW after each upgrade we need to check all
our drop-in directories against files, that enforce settings that render
our installs useless for our field of application.