`podman diff` reports `C /etc` (due to `hostname`)

[adelton]

Description of problem

This is a continuation of https://github.com/AlmaLinux/docker-images/issues/97, now for /etc/hostname.

Due to bug https://bugzilla.redhat.com/show_bug.cgi?id=1941142 which is present in all recent podman version as well, running podman diff on an AlmaLinux-based container reports C /etc even if nothing in the container changed. It's due to the fact that the container images do not contain /etc/hostname.

Steps to reproduce

$ podman run --name test-diff docker.io/almalinux/8-base date
$ podman diff test-diff
$ podman rm -f test-diff

Actual results

C /etc

Expected results

Nothing output by that podman diff command.

Additional information

I believe that this is caused by /etc/hostname missing on the image, similar to /etc/resolv.conf which got added in https://github.com/AlmaLinux/docker-images/pull/102.

[LKHN]

Thanks for the following the issue.

When I implemented the fix for /etc/resolv.conf file, it didn't show any diff anymore. So, I thought it would be enough.

OS: AlmaLinux OS 9.3 Podman: 4.6.1-5.el9 from Appstream repository.

git clone https://github.com/AlmaLinux/docker-images --single-branch
cd docker-images
podman build -t diff-test -f dockerfiles/al8/Dockerfile.base .
podman run --name test-diff localhost/diff-test date
Fri Nov 24 16:50:35 UTC 2023
podman diff test-diff

Now, I can reproduce the issue if I use the docker.io/almalinux/8-base image. I wonder what is the difference between the registry and local build one. :thinking:

[adelton]

I don't have a good insight into how things are built, as also mentioned in https://github.com/AlmaLinux/docker-images/issues/97#issuecomment-1741755310 where I saw the /etc/resolv.conf in an image I built locally.

[LKHN]

Here is: https://github.com/AlmaLinux/docker-images/blob/a95cef6a11ec939a6fa7b4f1a80cd1a0363b8cbc/docker_utils_functions#L310

[LKHN]

I just built it with docker as the pipeline does, can confirm that podman build creates the /etc/hostname but docker build doesn't.

[adelton]

Ah, so the problem is that during docker build, something is mounted there, so the touch or COPY --from=stage2 or something similar does not affect the resulting layer?

I wonder how Fedora / RHEL UBI images do that ...

[LKHN]

The touch method on #102 solved the half of the issue, what is left to add it for the /etc/hostname too, just tested with docker build and it works.

[adelton]

Ah, that is good news.

[LKHN]

Is anything else good with images? I'd like to hear your valuable feedback before proceed to build and publish with the proposed fix.

[adelton]

This should be the last thing I'm aware of WRT the images content.

[LKHN]

See the /etc/hostname inside the diff. https://github.com/docker-library/official-images/pull/15765#issuecomment-1826177022