On 08/10/2020 07:23, Hans-Werner Kneitinger wrote:
> Thank you for explanation but my use-case seems to be little different.
> Its for backup/recovery only. No need for file sharing between clients,
> all local only. The NAS is the central backup storage. No RPi user has
> an account on the NAS. I think there is no need for and its better to
> have less accounts as possible.
>
> The RPis are data collectors or controllers. I have a backup-image from
> every fresh setup and an RPi on cushion.
>
> 1. If an RPi or its SD Card dies, I restore from backup image and then
> restore latest data and setting from NAS.
>
> 2. If distro and/or hardware update is requiered, I do a fresh
> installation and a data restore from NAS.
>
> 3. No RPi user has access to the NAS but the special backup user.

That's probably your problem. You backup user is writing files which
have various Pi user and group id's to the NAS, and the NAS stores those
ids, as otherwise every file would belong to the backup user, which
isn't what you want.

But the NAS doesn't know about those users and groups, and their
relationship to the backup user. To allow the backup user to access
those files, they have to be set to world readable and writeable
i.e. 777

If you created matching users and groups on the NAS, and made sure the
backup user was part of those groups, the NAS would then know who was
allowed to access what, and the file permissions could then also be
stored correctly.

This is my interpretation of how NFS works, I may be wrong.

---druck

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