AIt applies a 3-way merge which solves simple conflicts automatically. But if there's a mismatch it leaves your file alone and you have to run a command to merge manually.
AIt's honestly harder to explain the actual behaviour and not worth going into details most of the time imo but here it is https://blog.verbum.org/2014/01/24/why-ostree-requires-usretc/
Colin WaltersColin Walters
While I often lump “dpkg/rpm” together since they’re very similar architecturally, their implementation of configuration file management is a small but nontrivial difference. This…
AOne cool thing is that since are the "ground truth templates", you can always run an ostree config diff to see what files you have changes in or files that you;'ve kept that don't exist upstream. 
AI think of it mostly as you explained because I don't count on that three way merge to work reliably
PYes that's what I was saying
It doesn’t attempt to understand the contents of files – if you have modified a config file in any way, that wins
AMm you're right 
AI read elsewhere that it's running a patch/diff, similar to this: Generate a patch between your and the new deployment's and then apply those patches to your and just ignore the ones that failed to apply.
ANot sure why he calls it a 3-way merge though if it is not merging anything
AYeah that blog is a mess of mixed up terms.
AOfficial docs are here and they mention the thing I just said: https://ostreedev.github.io/ostree/deployment/
PGitHub
Operating system and container binary deployment and upgrades - ostree/atomic-upgrades.md at 16cb47489e582da9c139fee20acdac7079867843 · ostreedev/ostree
ABut read this from the OSTree website:
When OSTree creates a deployment, it performs a 3-way merge using the old default configuration, the active system’s /etc, and the new default configuration. In the final filesystem tree for a deployment then, /etc is a regular writable directory.
PHow it works is:
- Files in the currently booted deployment's
which were modified from the default (of the same deployment) are retained./etc- Files in the currently booted deployment's
which were not modified from the default (of the same deployment) are upgraded to the new defaults from the new deployment's ./etc
AWhy does their own website contradict the part you just quoted?
PI don't think it's a contradiction do much as ambiguous use of the term "merge"
AYeah it could just be poorly explained. Grr.
PIndividual files aren't being merged, but the entire /etc tree is being merged in a very coarse grained way
AOh yeah that makes sense. What a poor way to phrase that on their site. I've always thought it did a 3-way merge per-file, not directory-wise.
AI've never even thought of directory comparisons as "3-way merging".
PYeah it's definitely not the best way to explain it without a bit more detail
AYeah, thanks for finding that, it's very useful to know. That changes how I'll maintain my system. I will run the "config diff" more often to resolve actual changes.
PIt's probably just a case of the people writing the docs being familiar enough with how it works that the explanation seems obvious enough - even though it's a bit unclear without the extra detail to someone not as familiar.
AYeah it's a common curse when trying to document a complex system that you're very familiar with.
PYeah my plan is to try to avoid touching things in /etc at all where possible
Ait'd be cool to have a script that does this and notifies
AYep, one thing I always do is edit the wireplumber config to add a script that disables audio device sleeping, to avoid that silent "popping" whenever audio begins playing again. I am doing it via some big edits.
I've been meaning to look for a way to install that in a more granular way that doesn't need maintenance constantly whenever wireplumber changes config.
I've been meaning to look for a way to install that in a more granular way that doesn't need maintenance constantly whenever wireplumber changes config.
AYeah good idea, some kinda GUI that runs as autostart on login and pops up if there's changes. dreams
dreamsPYeah I think having some kind of automated check that can keep tabs on the diff to prevent drift would be interesting
Ayou don't really need a gui, just run the command if there are changes send a dbus notification
PA bit complicated because there's a bunch of things that are probably going to be changed just by installing though, like /etc/passwd
AGreat idea 
AI wish anaconda put this stuff in /usr/etc before commiting the deployment to disk...
PEh but then should you be ending up with a new ostree deployment every time you change your password?
AI don't think it compares those files, like and
passwdW!!@ADD
AThat's dumb.
Ayeah they do appear as they are not in /usr/etc
AI'd be okay with that but there are some implications ...
Abut I would like it if does not destroy the system
Aconceptually that should reset the system to default state
PYeah, in a future where things are more image based "native" I could see something along those lines being the case
PI do see a /usr/etc/passwd and /usr/etc/shadow etc, but there's no passwords for any accounts, so a little hard to log in if things got reset to that 
(unless there's something that goes through the first boot setup again or something?)
(unless there's something that goes through the first boot setup again or something?)Apretty sure your system is bricked
Aif you remove them
Ryeah those files under /usr are probably only there to fix file not found errors
Athere are actual defaults for these files, wonder why those aren't used
ARI could see a future state where /etc/shadow /etc/group /etc/passwd actually become directories which get -d
Athat cannot happen, it breaks POSIX