podman: mount a file system during image build

Cavalcade

10/18/23, 6:48 PM

Using podman/buildah, I want to build a container image that has host file systems already mounted.

I am able to do this with Singularity with sudo singularity build /tmp/lolcow.simg /tmp/lolcow.recipe if those file systems are defined in /etc/singularity/singularity.conf. How can I do this with podman? I am trying to avoid using -v during the podman run stage for this. I'm not tied to Docker compatibility, so if there's a buildah-specific way to do this, great.

The podman-build man page gives as a usage example podman build --volume /home/test:/myvol:ro,Z -t imageName . But when I try it and run the resulting image, the equivalent of the /home/test file system isn't mounted.

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larsks

10/18/23, 11:16 PM

I want to build a container image that has host file systems already mounted.

You can't, primarily because such an image would present a substantial security risk (a container that could force arbitrary host mounts could happily export your entire filesystem to a malicious remote endpoint -- even when running as a non-root user this would still represent a fairly significant problem).

Using the --volume option to podman build mounts the volume inside the container during the build process, but there's no mechanism to instruct Podman (or Docker) to automatically mount something at runtime.

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Cavalcade

10/26/23, 12:18 AM

I follow you, but couldn't it mount in directories to which the building user has access? Singularity does something like this. Users who then try to start a container with that image cannot of course access any files their uid doesn't have access to. I should have mentioned everything I'm considering is rootless.

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