Re: debootstrap: enable --merged-usr by default

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Re: debootstrap: enable --merged-usr by default

Ian Jackson-2
I had a conversation with Marco about this at FOSDEM.  I'm sorry to
say that I still don't understand why we would make this change.

The links provided do not explain what the benefits are.  And there
are downsides.

One obvious downside is reduced testing of existing systems which have
filesystem layouts not easily compatible with "merged /usr" (or at
least, not compatible without wholesale moving of stuff about, which
seems like a risk which would need a substantial justification).

Another bad consequence is that some existing configurations that do
not, for whatever reason, mount /usr early, will be harder to set up.
One may argue (as Russ cogently does) that the distinction between
/usr and / cannot be coherently maintained as a distro-wide property
of software if we take into account all the realistic use cases.  But
there are some traditional configurations where the distinction _can_
be maintained and we shouldn't break those things without a reason.

Also, I fear that unless we provide a straightforward way to retain
separate /usr, including an appropriate d-i command line option, we
will get further pushback and anger from traditionalists.  We risk
reopening old wounds (see some of the less temperate responses earlier
in the thread Ansgar links to as [1]).  If there are benefits of
changing the default arrangement of new installs, it would be worth
thinking how those benefits could be obtained without the damage to
our community (even if the objections are felt, by many people, to be
technically unsound).

Finally, I have to say that I think that this summary from Ansgar
is not really accurate:

> As mentioned earlier, I would like to see --merged-usr enabled by
> default for Debian Stretch.  The last discussion on -devel@[1] was
> quite positive; I had some additional positive feedback on IRC.
...
> [1] <https://lists.debian.org/debian-devel/2016/09/msg00269.html>

That is a link to a message from Russ which mostly explains why
mounting /usr early (ie in the initramfs, by default) is a good idea.
That has now been implemented and has caused very little push-back.

But this bug report requests something entirely different: it is about
actually moving the contents of /bin into /usr/bin, etc.

It is also not fair to say that the discussion was "quite positive".
There was a good deal of opposition of various kinds, much of it
quite heated.

Thanks for your attention,
Ian.

--
Ian Jackson <[hidden email]>   These opinions are my own.

If I emailed you from an address @fyvzl.net or @evade.org.uk, that is
a private address which bypasses my fierce spamfilter.

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Re: Bug#839046: debootstrap: enable --merged-usr by default

Philip Hands
Hi Ian,

You're not citing any concrete examples of things that will supposedly
break.

AFAICS the closest you got was:

On Sat, 10 Feb 2018, Ian Jackson <[hidden email]> wrote:
> Another bad consequence is that some existing configurations that do
> not, for whatever reason, mount /usr early, will be harder to set up.

Which might be a fair point, except that late mounting of /usr became
explicitly unsupported with the release of Stretch:

  https://www.debian.org/releases/stretch/armel/release-notes/ch-information.en.html#late-mounting-usr

The adoption of usrmerge was blocked before on the basis that it was too
late in the release cycle.  We are now fairly early in the release cycle.

That being the case, I think we should let the people volunteering to do
the work to get on with it without delay. That way there will be plenty
of time to address any real downsides that might be revealed.

Cheers, Phil.

P.S. I've not even installed usrmerge on any systems as yet, so please
don't assume that I'm a rabid supporter of this effort -- it just seems
entirely sane to me, whereas the pushback you pointed at ... not so much.
--
|)|  Philip Hands  [+44 (0)20 8530 9560]  HANDS.COM Ltd.
|-|  http://www.hands.com/    http://ftp.uk.debian.org/
|(|  Hugo-Klemm-Strasse 34,   21075 Hamburg,    GERMANY

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Re: Bug#839046: debootstrap: enable --merged-usr by default

Philipp Kern-6
On 02/11/2018 02:40 PM, Philip Hands wrote:
> That being the case, I think we should let the people volunteering to do
> the work to get on with it without delay. That way there will be plenty
> of time to address any real downsides that might be revealed.

Something I did notice yesterday by accident is that ldd points to
libraries being loaded from /lib. Which is fine except that then you
can't put them into dpkg -S because dpkg does not know about the
aliasing that happens here. I suppose this is because /lib/* is listed
before /usr/lib/* in /etc/ld.so.conf.d/*-linux-gnu.conf. I suppose if
one wants to use the output to find the packages associated, one needs
to roundtrip through realpath once. But then again you might miss files
actually installed by dpkg into /lib.

So I think the question of "is there buy-in from the dpkg maintainers to
support the outcome" is not a bad one. ;-)

Kind regards
Philipp Kern


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