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Re: usrmerge -- plan B?




Marco d'Itri writes ("Re: usrmerge -- plan B?"):
> On Nov 20, Adam Borowski <kilobyte@xxxxxxxxxx> wrote:
> > Another question is, why?
> 
> It has been documented here long ago: https://wiki.debian.org/UsrMerge .

I looked at that page and it has no rationale.

> You are misconstructing the arguments in favour of merged-/usr to be 
> able to dismiss them easily.

I suspect you meant to refer to this:
   https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge/

I have read that.  IMO the arguments are extremely diffuse and
certainly do not justify the level of effort necessary to do this in a
rapid fashion (or, IMO, at all).


In this context it is important to realise that there would be serious
social costs to pressing ahead with making this mandatory: rightly or
wrongly, a significant minority of users and downstreams would
strongly dislike this change.  The nastiness and fighting which will
result if we press forward with this would far outweigh any minor
technical benefits of this simplification.

(In this context I want to repeat what Adam said about mounting /usr
in the initramfs.  That has removed the practical need to care, most
of the time, about whether a particular thing is in / or /usr.  So we
have already got most of the techical benefits.)


I have a perception that this change is part of a programme of
`tidying up'.  I have seen controversial changes proposed elsewhere,
which also seem largely motivated by a sense of `tidiness'.

As a general rule I think this is harmful.  `Tidying things up' is
fine if no-one cares about them.  If someone does care about them then
usually it is better to keep them, even if it is a small amount of
extra work, to maintain Debian as the most flexible base for
everyone's work.


I don't intend to do a point-by-point rebuttal of the whole
`TheCaseForTheUsrMerge' page, but it leads with `Compatibility', so I
will deal with the section `Compatibility: The Gist of It'.

1. "... scripts/programs written for other Unixes or other Linuxes and
   ported to your distribution will no longer need fixing for the file
   system paths of the binaries called, which is otherwise a major
   source of frustration ..."

The author of this text is obviously extremely easily frustrated.
Personally I have very rarely encountered any situation where the fact
that a particular binary was in /bin vs /usr/bin was any source of
frustration or even any trivial difficulty.  For interpreters, there
is generally a conventional #!  line that everyone uses.  Most of the
rest of the time programs use PATH.

There *is* trouble arounding executable locations: but it isn't / vs
/usr.  It's sbin vs libexec; and /usr vs /usr/local.  But usrmerge
does nothing to help those.

For modern programs everything tends to be in /usr[/local] anyway; for
older programs the compatibility arrangements are already in place.

2. Solaris compatibility

Well, this is a real argument.  But, seriously, do we care ?

3. "Maintaining the /usr split requires non-trivial project-specific
handling in the upstream build system".

I am not sure exactly what this point is.  AFAICT it is simply
complaining that if your package wants to ship files in / rather than
/usr, you need to do something in your *.install files or whatever.
This is true.  But it is not an argument in favour of making /bin a
symlink to /usr/bin.

Now that we mount /usr in the initramfs this can often be dispensed
with, along the lines of Adam's "plan B".  This can be done on a
package-by-package basis as the maintainer considers that the costs of
maintaining things in /bin becomes too high.  A maintainer can also
leave behind compatibility symlinks (the set of which is of course
closed).

4. "Improved compatibility with current upstream development"

I can't even figure out what this means.  Upstream programs that want
to ship everything in /usr are not a problem.


Ian.