mkfs.btrfs reproducibility

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 10/15/25 02:49, Qu Wenruo wrote:
> 
> 
> 在 2025/10/15 16:31, Demi Marie Obenour 写道:
>> On 10/15/25 01:47, Qu Wenruo wrote:
>>> 在 2025/10/15 16:13, Demi Marie Obenour 写道:
>>>> I need to create a BTRFS filesystem where /home and /tmp are BTRFS
>>>> subvolumes owned by root.  It's easy to create the subvolumes with
>>>> --subvol and --rootdir, but they wind up being owned by the user that
>>>> ran mkfs.btrfs, not by root.  I tried using fakeroot and it doesn't
>>>> work, regardless of whether fakeroot and btrfs-progs come from Arch
>>>> or Nixpkgs.
>>>>
>>>> What is the best way to do this without needing root privileges?
>>>> Nix builders don't have root access, and I don't know if they have
>>>> access to user namespaces either.
>>>
>>> Not familiar with namespace but I believe we can address it with some
>>> extra options like --pid-map and --gid-map options, so that we can map
>>> the user pid/gid to 0:0 in that case.
>>>
>>> Thanks,
>>> Qu
>>
>> Thank you!  This would be awesome.  In the meantime I worked around
>> the issue by having systemd-tmpfiles fix up the permissions.
> 
> Mind to share some details? I believe this will help other users, and I 
> can add a short note into the docs.

I fixed the owner and permissions at startup.  This is not good
because it means that the image is not reproducible.

Is it possible for mkfs.btrfs to be reproducible, or should one run
mkfs.btrfs at install-time instead of shipping the BTRFS image?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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