Help understanding how the owner and group of bind mounts is set

[edumserrano]

Hi,

I'm a docker desktop user on Windows and recently I've been trying to switch to using podman. I've come across a difference between podman and docker desktop that I'd like some help understanding.

If I run:

docker run --entrypoint /bin/sh -it -v ${PWD}:/app node:22.13.1 with podman and then inside the container I run ls -la /app I get the following:

drwxrwxrwx 1 node node 512 Feb 11 23:27 .
dr-xr-xr-x 1 root root 4096 Feb 11 23:36 ..
drwxrwxrwx 1 node node 512 Nov 13 14:38 file-1
-rwxrwxrwx 1 node node 321 Jan 28 23:57 file-2
drwxrwxrwx 1 node node 512 Jul 18 2024 file-3
-rwxrwxrwx 1 node node 615 Nov 6 13:26 file-4
...

but if I run the same commands using docker desktop the results of the ls -la /app show the owner and group as root instead of node.

Furthermore, if I use a named volume with podman, then group and owner are set to root. For instance in a compose file:

volumes:
  my-volume:
    external: false


services:
  my-service:
    image: [mcr.microsoft.com/playwright:v${PLAYWRIGHT_VERSION}-noble](node:22.13.1)
    working_dir: /app
    entrypoint: /bin/sh
    command:
      - -c
      - |
        ls -la
    volumes:
      - .:/app                          # this folder has owner and group set to node
      - my-volume:/test-dir   # this folder has owner and group set to root

It seems that for, bind mounts, podman chowns the directories to the UID of the default user of the image ?

Can someone help me understand:

1. Why this is the case and why the behaviour is different between podman and docker desktop ?
2. Why the behaviour in podman is different between bind mount and named volume ?
3. Can I achieve the same behaviour in podman that I get with docker desktop ? Meaning, in the above example, how can I get the user and owner of the bind mount for /app to be root instead of node ?

podman info

Also, in case it helps, here's the output of my podman info

Client:
  APIVersion: 5.4.0
  Built: 1739297196
  BuiltTime: Tue Feb 11 18:06:36 2025
  GitCommit: f9f7d48b24b1ca4403f189caaeab1cb8ff4a9aa2
  GoVersion: go1.23.6
  Os: windows
  OsArch: windows/amd64
  Version: 5.4.0
host:
  arch: amd64
  buildahVersion: 1.38.0
  cgroupControllers:
  - cpuset
  - cpu
  - cpuacct
  - blkio
  - memory
  - devices
  - freezer
  - net_cls
  - perf_event
  - net_prio
  - hugetlb
  - pids
  - rdma
  - misc
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon-2.1.12-2.fc40.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.12, commit: '
  cpuUtilization:
    idlePercent: 99.78
    systemPercent: 0.18
    userPercent: 0.04
  cpus: 16
  databaseBackend: sqlite
  distribution:
    distribution: fedora
    variant: container
    version: "40"
  eventLogger: journald
  freeLocks: 2036
  hostname: Kakashi-AMD
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 5.15.167.4-microsoft-standard-WSL2
  linkmode: dynamic
  logDriver: journald
  memFree: 15867588608
  memTotal: 16773365760
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns-1.13.1-1.fc40.x86_64
      path: /usr/libexec/podman/aardvark-dns
      version: aardvark-dns 1.13.1
    package: netavark-1.13.1-1.fc40.x86_64
    path: /usr/libexec/podman/netavark
    version: netavark 1.13.1
  ociRuntime:
    name: crun
    package: crun-1.19.1-1.fc40.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 1.19.1
      commit: 3e32a70c93f5aa5fea69b50256cca7fd4aa23c80
      rundir: /run/crun
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +CRIU +LIBKRUN +WASM:wasmedge +YAJL
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt-0^20241211.g09478d5-1.fc40.x86_64
    version: |
      pasta 0^20241211.g09478d5-1.fc40.x86_64
      Copyright Red Hat
      GNU General Public License, version 2 or later
        <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
      This is free software: you are free to change and redistribute it.
      There is NO WARRANTY, to the extent permitted by law.
  remoteSocket:
    exists: true
    path: unix:///run/podman/podman.sock
  rootlessNetworkCmd: pasta
  security:
    apparmorEnabled: false
    capabilities: CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_NET_BIND_SERVICE,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: false
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: false
  serviceIsRemote: true
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 4294967296
  swapTotal: 4294967296
  uptime: 0h 46m 9.00s
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - docker.io
store:
  configFile: /usr/share/containers/storage.conf
  containerStore:
    number: 10
    paused: 0
    running: 0
    stopped: 10
  graphDriverName: overlay
  graphOptions:
    overlay.imagestore: /usr/lib/containers/storage
    overlay.mountopt: nodev,metacopy=on
  graphRoot: /var/lib/containers/storage
  graphRootAllocated: 1081101176832
  graphRootUsed: 8899719168
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "true"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 10
  runRoot: /run/containers/storage
  transientStore: false
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 5.3.1
  Built: 1732147200
  BuiltTime: Thu Nov 21 00:00:00 2024
  GitCommit: ""
  GoVersion: go1.22.7
  Os: linux
  OsArch: linux/amd64
  Version: 5.3.1

[edumserrano]

Regarding question number 3, the only way I found to get the same behaviour was to set the automount.options in the wsl.conf of the podman-machine-default wsl distribution.

Steps:

1. Go into the wsl distribution used by podman: wsl --distribution podman-machine-default.
2. Edit the /etc/wsl.conf file to include:

[automount]
options="uid=0,gid=0"

3. Restart podman and wsl: podman machine stop, then wsl --shutdown and then podman machine start.

After the above steps, if I run a command with bind mount like docker run --entrypoint /bin/sh -it -v ${PWD}:/app node:22.13.1 and check the owner and group of /app in the container with ls -la /app it shows both as root instead node.

I am however uncertain of side effects of doing this...