podman run --userns fails with gidmapping=100:@${GID} but works with gidmapping=100:@${UID}

[Fak3]

Issue Description

When i run podman run --userns="auto:uidmapping=405:@${UID},gidmapping=100:@${GID}" --user guest alpine whoami, i get syntax error:
Error: parsing id map value "@": strconv.ParseUint: parsing "": invalid syntax

Steps to reproduce the issue

Run podman run --userns="auto:uidmapping=405:@${UID},gidmapping=100:@${GID}" --user guest alpine whoam

Describe the results you received

Error: parsing id map value "@": strconv.ParseUint: parsing "": invalid syntax

Describe the results you expected

This should replace ${GID} in the argument with the GID of the current user. The same way that it currently replaces ${UID} with current user's UID. For example, this command currently works fine:

> podman run --userns="auto:uidmapping=405:@${UID},gidmapping=100:@${UID}" --user guest  alpine whoami
guest

podman info output

host:
  arch: amd64
  buildahVersion: 1.38.0
  cgroupControllers:
  - pids
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon-2.1.12-1.2.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.12, commit: unknown'
  cpuUtilization:
    idlePercent: 91.28
    systemPercent: 2.58
    userPercent: 6.15
  cpus: 12
  databaseBackend: sqlite
  distribution:
    distribution: opensuse-tumbleweed
    version: "20250121"
  eventLogger: journald
  freeLocks: 2033
  hostname: localhost.localdomain
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 1001
      size: 1
    - container_id: 1
      host_id: 165536
      size: 65536
    uidmap:
    - container_id: 0
      host_id: 1001
      size: 1
    - container_id: 1
      host_id: 165536
      size: 65536
  kernel: 6.12.10-1-default
  linkmode: dynamic
  logDriver: journald
  memFree: 4434448384
  memTotal: 32985276416
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns-1.13.1-1.2.x86_64
      path: /usr/libexec/podman/aardvark-dns
      version: aardvark-dns 1.13.1
    package: netavark-1.13.1-1.1.x86_64
    path: /usr/libexec/podman/netavark
    version: netavark 1.13.1
  ociRuntime:
    name: crun
    package: crun-1.19.1-1.1.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 1.19.1
      commit: 3e32a70c93f5aa5fea69b50256cca7fd4aa23c80
      rundir: /run/user/1001/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-20241211.09478d5-1.2.x86_64
    version: |
      pasta 20241211.09478d5-1.2
      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: /run/user/1001/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: true
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: false
  serviceIsRemote: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns-1.3.1-1.2.x86_64
    version: |-
      slirp4netns version 1.3.1
      commit: unknown
      libslirp: 4.8.0
      SLIRP_CONFIG_VERSION_MAX: 5
      libseccomp: 2.5.5
  swapFree: 0
  swapTotal: 0
  uptime: 28h 30m 2.00s (Approximately 1.17 days)
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - registry.opensuse.org
  - registry.suse.com
  - docker.io
store:
  configFile: /home/u1/.config/containers/storage.conf
  containerStore:
    number: 14
    paused: 0
    running: 0
    stopped: 14
  graphDriverName: overlay
  graphOptions: {}
  graphRoot: /home/u1/.local/share/containers/storage
  graphRootAllocated: 234619252736
  graphRootUsed: 202116640768
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "false"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 1
  runRoot: /run/user/1001/containers
  transientStore: false
  volumePath: /home/u1/.local/share/containers/storage/volumes
version:
  APIVersion: 5.3.1
  Built: 1733485830
  BuiltTime: Fri Dec  6 16:50:30 2024
  GitCommit: ""
  GoVersion: go1.23.4
  Os: linux
  OsArch: linux/amd64
  Version: 5.3.1

Podman in a container

No

Privileged Or Rootless

Rootless

Upstream Latest Release

Yes

Additional environment details

No response

Additional information

No response

[eriksjolund]

I did a test on Fedora CoreOS 42.20241025.91.0

$ echo $UID
1046
$ echo $GID

$

According to
https://stackoverflow.com/a/39446268/757777
Bash sets the Bash variable UID .
In my example UID is not set as an environment variable:

$ printenv UID
$ printenv GID
$

Does it work if you set GID beforehand?

GID=$(id -g)

[eriksjolund]

I forgot to say:

Your shell does variable substitution of ${UID} and ${GID} in the command

podman run --userns="auto:uidmapping=405:@${UID},gidmapping=100:@${GID}" --user guest  alpine whoam

The actual command that will be run after shell variable substitution can be seen by running the same command but appending echo to the command-line:

echo podman run --userns="auto:uidmapping=405:@${UID},gidmapping=100:@${GID}" --user guest  alpine whoam

[Fak3]

Does it work if you set GID beforehand?

Thank you, It worked!