Place your system configuration files in /etc/
Hello BlueBuilders!
In this blog post, I will explain why the usage of /etc/ is now recommended over /usr/etc/ when building custom images of atomic Fedora.
We, and many others in the community have recommended previously that the system configuration files in custom images should be placed in /usr/etc/, while files in /etc/ are reserved for local-users. While it is true that in run-time the /usr/etc/ directory contains the original configuration of the image, this is technically undefined behavior build-time.
Technically, files written to /etc/ in the custom image are what populates /usr/etc/ on a system rebased to that image.
It is thanks to a recent discovery by the Universal Blue folks & the Rechunk developer Antheas that ostree has different behavior regarding /usr/etc/ & /etc/ in build-time vs in run-time.
Thanks to the RedHat employee & ostree maintainer Colin Walters who directly notified Universal Blue folks of this.
Why to transition
Section titled “Why to transition”When files are placed to /usr/etc/ in build-time, currently there are no issues & everything works as expected for now.
However, it is still not the ideal thing to do, since we are relying on undefined rpm-ostree behavior, which may stop working some time in the future.
Quoting Antheas:
When OSTree commits get converted to OCI, /usr/etc/ becomes /etc/. Then during deployment, new /etc/ files are silently moved to /usr/etc/.
Relying on /usr/etc/ to place modified files in customized packages is a hack and relies on undefined behavior in the rpm-ostree source code that performs the path rewriting.
(Take a note that we are utilizing an OCI image, so this part can be ignored: When OSTree commits get converted to OCI, /usr/etc/ becomes /etc/.)
As can be seen from the 1st paragraph of the note above, this is how ostree functions & this is why it’s desired to transition to /etc/.
/etc/ files in the image are copied to /usr/etc/ during deployment, so local-users will experience no changes.
How to transition
Section titled “How to transition”- It is highly recommended that you follow & complete The Caching Update & Updating the directory structure blog post updates
- If you’re working with a 1-to-1 filetree mapping structure, where you copy files & folders to the root (
/) folder, then do the following (source-folder is the folder defined insourcekey inside files module recipe entry):
- Move files from
files/system/usr/etc/tofiles/system/etc/(or replacesystemwith the name of the specific directory)
- If you copy files to the image in other ways, then any files that go to
/usr/etc/should be copied to go to/etc/according, including files copied by custom scripts. - You’re good to go! Commit your changes and wait to see that your custom image builds correctly.
