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Re: Nix and non-standard-toplevel-dir




Kai Harries <kai.harries@xxxxxxxxx> writes:

> I have filled an ITP for the Nix package-manager [1]. During packaging
> lintian pointed out [2] that Nix relies on a non-standard-toplevel-dir.

> The Nix package-manager keeps by default all packages in the path
> `/nix/store`. In principal this path can be changed, but it would make
> it impossible to use pre-build binaries from the standard Nixpkgs
> channels [3].

> The problem are retained dependencies. A package keeps references to
> a package it depends on. And this references contain the absolute
> path (including `/nix/store`).

> Section 5.5.3 and 6.1 of the PHD thesis "The Purely Functional
> Software Deployment Model" [4] on which Nix is based gives some more
> insight.

> I would like your advise on how to proceed.

I think this is a case where we should waive FHS for this package, due to
the unique nature of this package.

The top-level purpose of FHS is consistency on the system, partly for
other packages but primarily for the local systems administrator.  All
namespaces that aren't covered in FHS are implicitly reserved for the
local administrator, and they know that the distribution will use the FHS
directories for specific purposes and can set disk allocations, remote
mounts, and so forth accordingly.

Nix is effectively a completely different model and concept for how to lay
out software packages.  It's therefore not surprising that it doesn't
comply with the FHS, since it's not even trying to be the same sort of
system that the FHS anticipates.  It's an experiment with something new.

I think including the package manager in Debian, if possible, is a great
way to let Debian users experiment with some interesting concepts, and is
very much in line with our goals to be a universal operating system and to
provide a common basis for people to experiment and do interesting things.
Thank you for working on this!

I also don't think that anyone who installs and then uses the Nix package
manager is going to be surprised that it doesn't follow the FHS.  This is
pretty experimental stuff, and I doubt anyone is going to use it without
expecting it to be a bit weird.  If anything, they probably already know
how Nix works and are expecting it to use those paths.  There doesn't seem
to be much drawback in this carefully-chosen lack of compliance with the
FHS.

I don't think it's worth writing an explicit Policy exception for this,
since it's a single edge case.  Instead, I think it's a good use of a
Lintian override documenting what's going on.  Obviously, if Nix becomes
really popular in the long run, we can then go back and write this into
Policy.

-- 
Russ Allbery (rra@xxxxxxxxxx)               <http://www.eyrie.org/~eagle/>