podman/docs/source/markdown/options/group-add.md

--group-add=group | keep-groups

Assign additional groups to the primary user running within the container process.

• keep-groups is a special flag that tells Podman to keep the supplementary group access.

Allows container to use the user's supplementary group access. If file systems or devices are only accessible by the rootless user's group, this flag tells the OCI runtime to pass the group access into the container. Currently only available with the crun OCI runtime. Note: keep-groups is exclusive, you cannot add any other groups with this flag. (Not available for remote commands, including Mac and Windows (excluding WSL2) machines)