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Re: File ownership problem using removeable media



On Thu, Dec 27, 2018 at 06:48:51AM -0600, Richard Owlett wrote:
> On 12/25/2018 11:22 AM, tomas@tuxteam.de wrote:
> >On Tue, Dec 25, 2018 at 10:06:04AM -0600, Richard Owlett wrote:

[...]

> >>Linux intrinsically assumes one machine has multiple users.
> >
> >...and it is right in its assumption.
> 
> I will admit its assumption is typically valid.

It is *technically* valid: besides "your" user there's at least
"root", "daemon"; typically there's "bin", "man", often"www-data"
and more: lots of little gnomes catering to your well-being behind
the curtains. Have a look at /etc/passwd and behold...

> >>In *MY* case, one user has multiple machines.
> >
> >...and you're right in your assumption.
> 
> I ASSUME nothing! I make a statement of FACT ;/
> {I am the ONLY user on any of the machines.}

Fact? Complicated thing, that.

[...]

> Don't recall having been publicly referred to as sapient before ;/

I made an assumption, of course. But I'm ready to stand by it :-)

> >>I also have multiple instances of Debian installed on a physical
> >>machine. I routinely want something from another partition - Debian
> >>requires root access for that.
> >
> >You should be more precise: root access for what? > There are
> >several distinct "stages" in that access. Mounting? Read
> access?
> 
> While running the instance of Debian on sdaX I want read/write
> access to the files I own on the Debian on sdaY.

You skirted the question: this has been noticed.

When you "run the instance of Debian on sdaX": what do you have
to do to "access files on sdaY". Please, the whole process: you
boot your "Debian on sdaX" and then...

> >Mount is most definitely a root operation, and there are very strong
> >reasons for that (but things can be delegated).
> 
> In context, I don't understand "(but things can be delegated)".

Mounting a file system (what you call "sdaY" above) is the first thing
you have to do to be able to access the files in it. Actually this is
a bit imprecise, since "sdaY" is "the partition" [1], and you mount the
file system (hopefully) contained in it.

> >After mount, things
> >get very dependent on things (e.g. which file system, etc.)
> 
> For the purpose of this thread only one is ext4.

OK: this means that the file system has a notion of file owner
(and group) and will carry that around while you mount it "from"
different operating system instances. Since the file system remembers
UIDs and GIDs (not user and group names), your UIDs should be identical
across your different OS instances (you said this is so). And then
you shouldn't have a problem accessing your files.

> >>I'm wondering if some of my
> >>chaos/confusion stems from copying data from that partition to a
> >>flash drive.
> >
> >If you did the copy as root, didn't specify to keep file owner and
> >group (as in cp -p or cp -a) then yes, the owner/group of your copies
> >ends up as root.
> 
> I don't know what operations {or in what order} were performed on my
> collection of flash drives (~dozen).

No, but you should be able to assess the current state of affairs:
just do an "ls -l" on one of the files you expect to have access
to.

Cheers
-- t

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