podman image inspect compatibility with docker

[rgaiacs]

I'm working in a pull request to add official support to Podman into repo2docker, see jupyterhub/repo2docker#1471. When working in the pull request, one of the tests fails and my investigation result in notice that podman image inspect and docker image inspect produce different outputs.

Minimal Working Example

Consider the Dockerfile used by repo2docker for test in https://github.com/jupyterhub/repo2docker/blob/067e14a1af960c0979b04b6a65e663bb1943ef08/tests/dockerfile/simple/Dockerfile

FROM python:3.10

RUN pip install --no-cache notebook

CMD "/bin/sh"

ADD sayhi.sh /usr/local/bin/sayhi.sh
ADD verify verify

ARG NB_UID
ENV HOME /tmp
USER $NB_UID

Expected

podman build and docker build successfully create container images.

podman image inspect and docker image inspect produce similar outputs.

Observed

podman build and docker build successfully create container images.

podman image inspect and docker image inspect produce different outputs, for example docker image inspect includes

[{
  ...
  "Config": {
    ...
    "WorkingDir": ""
    ...
  }
  ...
}]

The `WorkingDir` keyword is missing in the `docker image inspect` output.

### Docker

```json
[
    {
        "Id": "sha256:305803fc19b5fbecde4148823e435cfb86473271888c20ba967fc8871d0b9842",
        "RepoTags": [
            "1471-docker:latest"
        ],
        "RepoDigests": [
            "1471-docker@sha256:305803fc19b5fbecde4148823e435cfb86473271888c20ba967fc8871d0b9842"
        ],
        "Parent": "",
        "Comment": "buildkit.dockerfile.v0",
        "Created": "2025-10-17T12:27:15.963157482Z",
        "DockerVersion": "",
        "Author": "",
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 466303036,
        "GraphDriver": {
            "Data": null,
            "Name": "overlayfs"
        },
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:a5ec5ec9d16c5551ce8889cbc03af0609b92cf8a8d60b32e72a7eabb8378eaec",
                "sha256:1260506aec8337c2cec7368e24bdffda09aaeecfea85838748b9ebf2b2b3d40b",
                "sha256:698d92e1248de62fa4f689f9ff4cdeaa3ef252a52a6176ca86f481d441a1fc06",
                "sha256:25bde18331a66770e74ee7b8f45dd615d545b2d26f54b2258339fbbf3db8e390",
                "sha256:96c3316d3323a5254e1eb4c6622492ec251ac73e988ba2157943b3ecd348aa11",
                "sha256:71335cd8ec7dff657e34083bcaee6a9819ccf41e4f9efa2874cea0e2f6b72e25",
                "sha256:2d312de0bef39006e186a8854d72b9a796f3b042770e79b5e86017ca73f85b59",
                "sha256:d80ca80396c9d1351d6132b272b2444bcc0a13b9f62c3f868014148069686af0",
                "sha256:6bf05f5f01e38750f766234156bc2d92e28f774f65de60af74a1db7be586ba6e",
                "sha256:6bcfc6ba45d4ac87c6292e00467275b1d75f75d13f0ea06897736c6b233c2ee1"
            ]
        },
        "Metadata": {
            "LastTagTime": "2025-10-17T13:16:10.058906262Z"
        },
        "Descriptor": {
            "mediaType": "application/vnd.oci.image.index.v1+json",
            "digest": "sha256:305803fc19b5fbecde4148823e435cfb86473271888c20ba967fc8871d0b9842",
            "size": 856
        },
        "Config": {
            "ArgsEscaped": true,
            "Cmd": [
                "/bin/sh",
                "-c",
                "\"/bin/sh\""
            ],
            "Entrypoint": null,
            "Env": [
                "PATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "LANG=C.UTF-8",
                "GPG_KEY=A035C8C19219BA821ECEA86B64E628F8D684696D",
                "PYTHON_VERSION=3.10.19",
                "PYTHON_SHA256=c8f4a596572201d81dd7df91f70e177e19a70f1d489968b54b5fbbf29a97c076",
                "HOME=/tmp"
            ],
            "Labels": null,
            "OnBuild": null,
            "User": "",
            "Volumes": null,
            "WorkingDir": ""
        }
    }
]

Podman

[
     {
          "Id": "98d155a4672316e421532fdca3603c8952403e7835e0b1faf42e75242092434a",
          "Digest": "sha256:64ce7bb1c0c786a3fdc52215151d5a842c87c592e6e2b0439d4bf451c74d3b6f",
          "RepoTags": [
               "localhost/1471-podman:latest"
          ],
          "RepoDigests": [
               "localhost/1471-podman@sha256:64ce7bb1c0c786a3fdc52215151d5a842c87c592e6e2b0439d4bf451c74d3b6f"
          ],
          "Parent": "6397cd8bcf9f55ba484893182ebb6a4af127654d3359d3d44aa60614bc94bb7b",
          "Comment": "debuerreotype 0.16",
          "Created": "2025-10-17T13:14:11.326212892Z",
          "Config": {
               "Env": [
                    "PATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                    "LANG=C.UTF-8",
                    "GPG_KEY=A035C8C19219BA821ECEA86B64E628F8D684696D",
                    "PYTHON_VERSION=3.10.19",
                    "PYTHON_SHA256=c8f4a596572201d81dd7df91f70e177e19a70f1d489968b54b5fbbf29a97c076",
                    "HOME=/tmp"
               ],
               "Cmd": [
                    "/bin/sh",
                    "-c",
                    "\"/bin/sh\""
               ],
               "Labels": {
                    "io.buildah.version": "1.41.5"
               }
          },
          "Version": "",
          "Author": "",
          "Architecture": "amd64",
          "Os": "linux",
          "Size": 1345241114,
          "VirtualSize": 1345241114,
          "GraphDriver": {
               "Name": "overlay",
               "Data": {
                    "LowerDir": "/home/raniere/.local/share/containers/storage/overlay/bd16eee140196e07b771149d72de4b08bdc0383354b61ad615ccecec9d579755/diff:/home/raniere/.local/share/containers/storage/overlay/dfc9cc9c6df7c8325c85e145ba41ad262a73c761610904054e0de711e63553bc/diff:/home/raniere/.local/share/containers/storage/overlay/5caa9c20af27eae8c3968040d912060f9d16b10c2c72e02c8be11c47e648f8ed/diff:/home/raniere/.local/share/containers/storage/overlay/c160c8d960d57315ace3b6e21f8848d4115c088bfba14f8aa23690eefb88fe81/diff:/home/raniere/.local/share/containers/storage/overlay/10d7221da0dd01ce4a69ebec21c752ebfe5bbb763e0eadc4d704e310d10c75ae/diff:/home/raniere/.local/share/containers/storage/overlay/dfb41b1ca3704cb827860cd6a54dcd43f099b531c0082df43821ba85086b190c/diff:/home/raniere/.local/share/containers/storage/overlay/c555b6b2553fd6ced83691a0321c1ff1132e62f01a90af54c3cdcd0d31054a94/diff:/home/raniere/.local/share/containers/storage/overlay/c5f94038da422389702d4c1812962dceceea285b3f946086f5751f0724771ab1/diff:/home/raniere/.local/share/containers/storage/overlay/a5ec5ec9d16c5551ce8889cbc03af0609b92cf8a8d60b32e72a7eabb8378eaec/diff",
                    "UpperDir": "/home/raniere/.local/share/containers/storage/overlay/17349afeaf56d1ee4826908ef6b2cb1618503d8efdba5ee87f1b2443d62e0310/diff",
                    "WorkDir": "/home/raniere/.local/share/containers/storage/overlay/17349afeaf56d1ee4826908ef6b2cb1618503d8efdba5ee87f1b2443d62e0310/work"
               }
          },
          "RootFS": {
               "Type": "layers",
               "Layers": [
                    "sha256:a5ec5ec9d16c5551ce8889cbc03af0609b92cf8a8d60b32e72a7eabb8378eaec",
                    "sha256:1260506aec8337c2cec7368e24bdffda09aaeecfea85838748b9ebf2b2b3d40b",
                    "sha256:698d92e1248de62fa4f689f9ff4cdeaa3ef252a52a6176ca86f481d441a1fc06",
                    "sha256:25bde18331a66770e74ee7b8f45dd615d545b2d26f54b2258339fbbf3db8e390",
                    "sha256:96c3316d3323a5254e1eb4c6622492ec251ac73e988ba2157943b3ecd348aa11",
                    "sha256:71335cd8ec7dff657e34083bcaee6a9819ccf41e4f9efa2874cea0e2f6b72e25",
                    "sha256:2d312de0bef39006e186a8854d72b9a796f3b042770e79b5e86017ca73f85b59",
                    "sha256:38cae2470b747dd91289cd4de1287614f28a3235bca0d16e2a8ad3f00f7d5bd2",
                    "sha256:5bd49cfa37ad101fdc7e6b9f7f88e69f99b768c801df339b7b4c76d16c4e1c50",
                    "sha256:6bcfc6ba45d4ac87c6292e00467275b1d75f75d13f0ea06897736c6b233c2ee1"
               ]
          },
          "Labels": {
               "io.buildah.version": "1.41.5"
          },
          "Annotations": {
               "com.docker.official-images.bashbrew.arch": "amd64",
               "org.opencontainers.image.base.digest": "sha256:f10ac4838d35e60d5dba3149a49c22945bffcf50fa3f167fb2cc82f9063efd93",
               "org.opencontainers.image.base.name": "docker.io/library/python:3.10",
               "org.opencontainers.image.created": "2025-10-17T13:14:11.326212892Z",
               "org.opencontainers.image.revision": "54a65f4ff531391810946ee17b0806accbda0fae",
               "org.opencontainers.image.source": "https://github.com/docker-library/python.git#54a65f4ff531391810946ee17b0806accbda0fae:3.10/trixie",
               "org.opencontainers.image.url": "https://hub.docker.com/_/python",
               "org.opencontainers.image.version": "3.10.19-trixie"
          },
          "ManifestType": "application/vnd.oci.image.manifest.v1+json",
          "User": "",
          "History": [
               {
                    "created": "2024-01-31T23:01:46Z",
                    "created_by": "# debian.sh --arch 'amd64' out/ 'trixie' '@1759104000'",
                    "comment": "debuerreotype 0.16"
               },
               {
                    "created": "2024-01-31T23:01:46Z",
                    "created_by": "RUN /bin/sh -c set -eux; \tapt-get update; \tapt-get install -y --no-install-recommends \t\tca-certificates \t\tcurl \t\tgnupg \t\tnetbase \t\tsq \t\twget \t; \tapt-get dist-clean # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2024-01-31T23:01:46Z",
                    "created_by": "RUN /bin/sh -c set -eux; \tapt-get update; \tapt-get install -y --no-install-recommends \t\tgit \t\tmercurial \t\topenssh-client \t\tsubversion \t\t\t\tprocps \t; \tapt-get dist-clean # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2024-01-31T23:01:46Z",
                    "created_by": "RUN /bin/sh -c set -ex; \tapt-get update; \tapt-get install -y --no-install-recommends \t\tautoconf \t\tautomake \t\tbzip2 \t\tdefault-libmysqlclient-dev \t\tdpkg-dev \t\tfile \t\tg++ \t\tgcc \t\timagemagick \t\tlibbz2-dev \t\tlibc6-dev \t\tlibcurl4-openssl-dev \t\tlibdb-dev \t\tlibevent-dev \t\tlibffi-dev \t\tlibgdbm-dev \t\tlibglib2.0-dev \t\tlibgmp-dev \t\tlibjpeg-dev \t\tlibkrb5-dev \t\tliblzma-dev \t\tlibmagickcore-dev \t\tlibmagickwand-dev \t\tlibmaxminddb-dev \t\tlibncurses5-dev \t\tlibncursesw5-dev \t\tlibpng-dev \t\tlibpq-dev \t\tlibreadline-dev \t\tlibsqlite3-dev \t\tlibssl-dev \t\tlibtool \t\tlibwebp-dev \t\tlibxml2-dev \t\tlibxslt-dev \t\tlibyaml-dev \t\tmake \t\tpatch \t\tunzip \t\txz-utils \t\tzlib1g-dev \t; \tapt-get dist-clean # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "ENV PATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "ENV LANG=C.UTF-8",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "RUN /bin/sh -c set -eux; \tapt-get update; \tapt-get install -y --no-install-recommends \t\tlibbluetooth-dev \t\ttk-dev \t\tuuid-dev \t; \tapt-get dist-clean # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "ENV GPG_KEY=A035C8C19219BA821ECEA86B64E628F8D684696D",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "ENV PYTHON_VERSION=3.10.19",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "ENV PYTHON_SHA256=c8f4a596572201d81dd7df91f70e177e19a70f1d489968b54b5fbbf29a97c076",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "RUN /bin/sh -c set -eux; \t\twget -O python.tar.xz \"https://www.python.org/ftp/python/${PYTHON_VERSION%%[a-z]*}/Python-$PYTHON_VERSION.tar.xz\"; \techo \"$PYTHON_SHA256 *python.tar.xz\" | sha256sum -c -; \twget -O python.tar.xz.asc \"https://www.python.org/ftp/python/${PYTHON_VERSION%%[a-z]*}/Python-$PYTHON_VERSION.tar.xz.asc\"; \tGNUPGHOME=\"$(mktemp -d)\"; export GNUPGHOME; \tgpg --batch --keyserver hkps://keys.openpgp.org --recv-keys \"$GPG_KEY\"; \tgpg --batch --verify python.tar.xz.asc python.tar.xz; \tgpgconf --kill all; \trm -rf \"$GNUPGHOME\" python.tar.xz.asc; \tmkdir -p /usr/src/python; \ttar --extract --directory /usr/src/python --strip-components=1 --file python.tar.xz; \trm python.tar.xz; \t\tcd /usr/src/python; \tgnuArch=\"$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)\"; \t./configure \t\t--build=\"$gnuArch\" \t\t--enable-loadable-sqlite-extensions \t\t--enable-optimizations \t\t--enable-option-checking=fatal \t\t--enable-shared \t\t$(test \"${gnuArch%%-*}\" != 'riscv64' && echo '--with-lto') \t\t--with-ensurepip \t; \tnproc=\"$(nproc)\"; \tEXTRA_CFLAGS=\"$(dpkg-buildflags --get CFLAGS)\"; \tLDFLAGS=\"$(dpkg-buildflags --get LDFLAGS)\"; \tmake -j \"$nproc\" \t\t\"EXTRA_CFLAGS=${EXTRA_CFLAGS:-}\" \t\t\"LDFLAGS=${LDFLAGS:-}\" \t; \trm python; \tmake -j \"$nproc\" \t\t\"EXTRA_CFLAGS=${EXTRA_CFLAGS:-}\" \t\t\"LDFLAGS=${LDFLAGS:--Wl},-rpath='\\$\\$ORIGIN/../lib'\" \t\tpython \t; \tmake install; \t\tbin=\"$(readlink -ve /usr/local/bin/python3)\"; \tdir=\"$(dirname \"$bin\")\"; \tmkdir -p \"/usr/share/gdb/auto-load/$dir\"; \tcp -vL Tools/gdb/libpython.py \"/usr/share/gdb/auto-load/$bin-gdb.py\"; \t\tcd /; \trm -rf /usr/src/python; \t\tfind /usr/local -depth \t\t\\( \t\t\t\\( -type d -a \\( -name test -o -name tests -o -name idle_test \\) \\) \t\t\t-o \\( -type f -a \\( -name '*.pyc' -o -name '*.pyo' -o -name 'libpython*.a' \\) \\) \t\t\\) -exec rm -rf '{}' + \t; \t\tldconfig; \t\texport PYTHONDONTWRITEBYTECODE=1; \tpython3 --version; \t\tpip3 install \t\t--disable-pip-version-check \t\t--no-cache-dir \t\t--no-compile \t\t'setuptools==79.0.1' \t\t'wheel<0.46' \t; \tpip3 --version # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "RUN /bin/sh -c set -eux; \tfor src in idle3 pip3 pydoc3 python3 python3-config; do \t\tdst=\"$(echo \"$src\" | tr -d 3)\"; \t\t[ -s \"/usr/local/bin/$src\" ]; \t\t[ ! -e \"/usr/local/bin/$dst\" ]; \t\tln -svT \"$src\" \"/usr/local/bin/$dst\"; \tdone # buildkit",
                    "comment": "buildkit.dockerfile.v0"
               },
               {
                    "created": "2025-10-09T21:44:07Z",
                    "created_by": "CMD [\"python3\"]",
                    "comment": "buildkit.dockerfile.v0",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-17T06:52:38.750204428Z",
                    "created_by": "/bin/sh -c pip install --no-cache notebook",
                    "comment": "FROM docker.io/library/python:3.10"
               },
               {
                    "created": "2025-10-17T06:52:40.963206074Z",
                    "created_by": "/bin/sh -c #(nop) CMD \"/bin/sh\"",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-17T06:52:41.119662534Z",
                    "created_by": "/bin/sh -c #(nop) ADD file:db84ea52555824a6094aa5d931eeb9dc20336e66717850f5fe57378b02e4100a in /usr/local/bin/sayhi.sh      "
               },
               {
                    "created": "2025-10-17T06:52:41.368620191Z",
                    "created_by": "/bin/sh -c #(nop) ADD file:308a44cb0d05787d54753f874868528d7a34851e4b1d6a70bff8f03568e598b8 in verify      "
               },
               {
                    "created": "2025-10-17T13:14:11.234413185Z",
                    "created_by": "/bin/sh -c #(nop) ARG ",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-17T13:14:11.274689709Z",
                    "created_by": "/bin/sh -c #(nop) ENV HOME /tmp",
                    "empty_layer": true
               },
               {
                    "created": "2025-10-17T13:14:11.326684025Z",
                    "created_by": "/bin/sh -c #(nop) USER $NB_UID",
                    "empty_layer": true
               }
          ],
          "NamesHistory": [
               "localhost/1471-podman:latest"
          ]
     }
]