Volume folder's group is mapped to nogroup when --userns=keep-id is used

[franzwong]

I can use --userns=keep-id:uid=1000,gid=1000 to map the user but not the group.

I am using podman 4.6.0 (rootless)

I created a directory on my host machine. (franz is current user on host machine, staff is the primary group)

drwxr-xr-x 3 franz staff  96 Jul 29 11:20 app

Here is the Dockerfile. A user foo (uid: 1000) and a group bar (gid: 1000) are created.

FROM ubuntu:22.04
ENTRYPOINT ["bash"]
RUN groupadd -g 1000 bar
RUN useradd -u 1000 -g 1000 -m foo
USER foo

Then I started the container with --userns=keep-id:uid=1000,gid=1000.

podman run --userns=keep-id:uid=1000,gid=1000 -it --rm -v /test/app:/usr/app test_image

However, the group is nogroup when I checked the mounted directory.

foo@4f64145ccbef:/$ ls -l /usr
drwxr-xr-x. 3 foo  nogroup   96 Jul 29 02:20 app

I expect the group is bar. Do I misuse ---userns=keep-id?