[chpatrick]

> Sorry for being dense, but I thought one of the main reason for nixos's existence is reproducibilty. I thought they have these kinds of things solved already.

Nixos has the advantage that everything is built in its own sandbox with only its explicitly declared (and hashed) dependencies available, unlike in mainstream distros where it's the full system environment, so in many cases you already get the same binary every time. But this doesn't immediately lead to reproducibility because the build process might be nondeterministic for various packages.

[goodpoint]

> unlike in mainstream distros

Debian has been building in a clean sandbox with only required, tracked dependencies since decades.

It's also building the large majority of packages reproducibly including the binary and whole installation packages (not just the sources like nixos)

[chpatrick]

> not just the sources like nixos

Not sure what you mean by that, the Nix packages that are reproducible have reproducible binaries.

In the Nixos world there isn't really a concept of a "binary/installation package" like in Debian or elsewhere. Everything can be rebuilt from source on any machine, but because everything is hashed, if the official binary caches have already built something with the same inputs, they can just give you the outputs directly. So it's more like memoization than a .deb or something that you install.

Nix is a functional language that builds recipes (derivations) to build stuff, with all the inputs and outputs hashed. If the derivation you want to build has already been built by a cache you trust, the system will just fetch it instead of building locally.

What the Nix reproducability project checks is that the same derivation produces the same output regardless of what machine it's built on.

[JamesSwift]

> In the Nixos world there isn't really a concept of a "binary/installation package" like in Debian or elsewhere. Everything can be rebuilt from source on any machine

Thats not actually the case. A derivation is just an abstract concept that combines a hash with a "thing". Here is an example [1] of a pre-compiled mono binary that gets downloaded and installed (after patching paths).

[1] - https://github.com/NixOS/nixpkgs/blob/0cbe9f69c234a7700596e9...

[WhyNotHugo]

> unlike in mainstream distros where it's the full system environment

Usually packages are built in an environment which has only a minimal base system plus the package's explicitly dependencies. They don't have random unnecessary packages installed.

[benreesman]

This is a really good comment, I have no idea why it’s going grey.

Upvote from me FWIW.