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Re: problems with manual page usermod.8 and useradd.8

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On Thu, Feb 22, 2018 at 10:12:44PM +0100, MarkusHiereth wrote:
> Hello,
> when updating the German translations of the shadow package, I
> encountered strange things in the documentation. For example an option
> --non-unique for the commands useradd and usermod. With the first, the
> system administrator is able to force the system to create a new user
> with an ID that already exists, which is related to another user.
> One effect I would expect after using useradd with this option is that
> files and directories are owned by two persons - as the UID of a file
> indicates the owner.

No. The relevant bit of information are the "numbers" (UID, GID), and
those files carry just one of each. The number itself has several
"names", i.e. UID 1000 has two names, "sally" and "mike".

(This is a pattern you'll find at many places in the Unixoid culture:
one inode can be referred by several directory entries (aka one "file"
can have several "names"), an IP address can have several DNS entries,
yadda, yadda).

David Wright already hinted at that, but I'm not sure whether this was
clear enough for someone not familiar with the concept.

> Has anybody an idea about the purpose of such an option?

Hm. Dunno. Perhaps there are programs out there which insist in having
a fixed user/group name for some function. Soft transitions. That kind
of thing.

- -- tomás
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