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A reported rootless podman export produced a tar archive in which file owners appeared shifted, even though the command returned exit status 0. That is a case report, not a documented rule for every Podman release or setup. Rootless user-namespace mappings explain why container IDs and host IDs can differ, but Podman’s export documentation does not promise that archive owner IDs are normalized to the invoking user.
What does a successful export with shifted owners mean?
podman export writes a container’s filesystem to a tar archive and flattens it into one layer. In the reported case, the command returned 0 while the archive’s owner IDs differed from the expected values. A zero exit status reports that the command did not signal failure through that status; it does not establish that the tar headers contain the ownership values you intended.
The report does not establish a Podman version, host configuration, exact namespace mapping, or independently verified archive metadata. The official podman-export reference defines the export operation but does not document an owner-ID conversion guarantee. Treat the shift as something to diagnose in your environment, not as universal behavior.
Why keep-id does not guarantee host-style archive owners
Rootless Podman runs containers in a user namespace. Numeric IDs inside that namespace can correspond to different IDs on the host, depending on the mapping and subordinate UID/GID ranges. Podman’s v6.1.3 run manual describes --userns=keep-id as mapping the invoking user’s UID and GID to the same values inside the container; optional uid= and gid= values can select container IDs. Unless overridden with --user, the container’s init process runs under that mapped identity.
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This describes a namespace mapping, not a promise about how a later export command writes ownership into tar headers. The rootless tutorial also distinguishes the identity visible inside the container from the host IDs used by the namespace. The name keep-id should not be read as “rewrite every archived file owner to the host user.”
First distinguish the artifact you need
| Command | What it archives | Relevant distinction |
|---|---|---|
podman export |
The container filesystem as a flattened tar archive. | Use when you need the container filesystem. The reference does not state an owner-ID normalization guarantee. |
podman save |
An image archive that retains image layers, history, and tags. | Use when you need to archive or transfer an image. It is not a drop-in replacement for exporting a container’s filesystem. |
These semantics are described in the Podman export documentation. Choose based on whether the required object is a container filesystem or an image; changing commands alone does not establish that the resulting ownership metadata will match a particular expectation.
How to verify where the IDs change
Compare numeric IDs at each stage instead of relying on owner names. Names shown by ls are resolved using account databases and can obscure differences in the underlying UID or GID.
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podman version, the host UID/GID, whether Podman is rootless, and the relevant/etc/subuidand/etc/subgidranges. - Record the container mapping. Note whether
keep-iduses its defaults or explicituid=/gid=values. Inspect the effective mapping withpodman inspectorpodman unshare; where applicable, inspect/proc/self/uid_mapand/proc/self/gid_map. - Check ownership inside the container. Record numeric UID/GID values for the files in question, not only displayed user and group names.
- Inspect the tar headers. Compare the numeric UID/GID stored in the exported archive with the container-side values. This identifies whether the values differ in the artifact, rather than merely looking different in a host-side listing.
- Confirm the intended operation. If you need an image archive with layers and metadata, evaluate
podman save; if you need the container filesystem, stay with the export path and investigate its archive headers.
This is a diagnostic workflow, not a claim that any particular release must produce a specific mapping in its tar output.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep volume ownership troubleshooting separate
Files created by rootless containers can appear on the host with subordinate UID/GID numbers. Podman’s troubleshooting guide describes using podman unshare to work with files under the user namespace and discusses keep-id:uid=...,gid=... for mapping the container identity to the invoking host user.
Those instructions address host-side files and volumes. They may help interpret or manage filesystem ownership, but they do not by themselves establish how podman export serializes owner IDs into a tar archive.
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What is established—and what is not
- Documented: Rootless containers use user-namespace mappings, and the same numeric UID/GID can have different meanings inside the container and on the host.
- Documented:
keep-idmaps the invoking user into the container, with explicit container IDs available in the documented options. - Reported, not generalized: One practitioner case describes shifted owners in an exported tar and exit status 0. The full report was not retrievable, so its exact version and setup are not established.
- Not documented in the export reference: A guarantee that exported tar ownership will be converted to host-user IDs, or a general explanation for the reported shift.
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