[__MatrixMan__]

Have you found that nix-store --gc breaks things, or are you concerned that it's not an aggressive enough garbage collection?

When I have space problems, I run that and they're gone, then later I do it again. It could be that I'm just avoiding functionality that it breaks though.

[d3Xt3r]

There's still leftovers. For me, it's not about space problem, but more of wanting to run a tight ship. Most recently, I tried running all the stuff on the wiki[1] but I still had leftovers that wouldn't go away no matter what (these were some CUDA dependencies, if it makes a difference). In the end I ended up blowing away my entire Nix install, manually deleting the store and reinstalling Nix - which isn't exactly ideal - considering that the whole point of Nix is to be deterministic and reproducible and all that jazz... so to me it doesn't make sense that it dirties the host and doesn't clean up after itself. Since then I've gone back to using containers as at least they don't pollute the host, and I feel like I'm in greater control over the entire environment.

[1] https://nixos.wiki/wiki/Cleaning_the_nix_store

[__MatrixMan__]

I salute your desire to run a tight ship. If there were a leak in the nix store, I'd never know until I my garbage collection stopped solving the problem and I'm sure it would be at the worst possible time. If such a leak exists and is found, it'll be by someone running a tight ship.

Instead of running a tight ship I spend a lot of time dreaming about alternate computational universes, and one I particularly like is where new hard disks come pre-loaded with a fragment of bits deemed culturally valuable. Wikipedia and a well curated subset of nixpkgs would be a fine start to such an archive. In this world your files don't grow/shrink to consume/yield empty space, but rather the boundary between your data and that drive's shard of the public archive shifts in one direction or another. This way you or somebody in your neighborhood is likely to already have the file you need, so you can get it from them instead of the internet. Better for being able to roll with the punches if the internet is partitioned.

I don't worry about the size of the nix store because according to this weird fantasy of mine it's on the side of my disk that shrinks when I add files to it; it's not the contained object, but the gas that expands to fill the rest of the container. Not by accident, but as part of a redundant worldwide distributed cache that we put together after deciding that servers controlled by people we don't know are not to be relied on.

[neobrain]

I feel your pain on this one despite being fairly comfortable with nix by now. This is 100% an issue either the documentation or the nix CLI should do a better job at.

The wiki rightfully points towards "roots", i.e. references produced by nix-build or similar. Additionally, there are other places that will keep references and hence block garbage collection though:

1. Your nix profile (`nix profile list` / `nix profile remove`) and its old generations (`nix profile (wipe-)history`)

2. Your NixOS configuration (configuration.nix) and its old generations (`nixos-rebuild list-generations`)

It doesn't help that there's no discoverable way to tell why a particular nix store path is not being garbage collected either.