Reuse /run/current-system/sw instead of /run/system-manager

[bryango]

Is your feature request related to a problem? Please describe.

I was trying to adapt nixos modules for system-manager and noticed that many of them have hard-coded /run/current-system/sw; see e.g.

• https://github.com/search?q=repo%3ANixOS%2Fnixpkgs+%2Frun%2Fcurrent-system%2Fsw+NOT+path%3A%2F%5Enixos%5C%2Ftests%5C%2F%2F&type=code

One must modify /run/current-system -> /run/system-manager in order to port such modules.

Describe the solution you'd like

Since /run/current-system is not used in a generic non-NixOS system I believe we can simply re-use the path.

Describe alternatives you've considered

• As mentioned before, rename each /run/current-system -> /run/system-manager module by module.
• Alternatively, provide an option to symlink /run/current-system -> /run/system-manager when profiles are activated.

Additional context

I am not sure if it's safe to do this. It feels safe to me since system-manager should only be used on non-NixOS so there will not be conflicts. But I don't know.

[r-vdp]

I'd prefer doing the symlink and making it optional, so that it can be turned off in case anyone has issues with it.

[bryango]

Oh I just noticed that NixOS itself is on the list of supported systems:

system-manager/nix/modules/default.nix

Lines 139 to 145 in 549bc38

	system-manager.preActivationAssertions = {
	osVersion =
	let
	supportedIds = [ "nixos" "ubuntu" ];
	in
	{
	enable = !config.system-manager.allowAnyDistro;

So indeed it should be an option that one can toggle on or off.

[sellout]

To help make modules more portable, is there some attribute that would return /run/current-system/sw in a nixosModule and /run/system-manager on a systemModule? I’d be happy to fix the hardcoding of /run/current-system/sw in nixpkgs if so.

[r-vdp]

I don't think we have that right now, but it would be rather easy to introduce an option for this. It might be a rather hard sell to get that merged into nixpkgs though.

[aanderse]

It might be a rather hard sell to get that merged into nixpkgs though.

i suggest there is prior art for a change like this

additionally, with more and more nix based systems popping up i think this is a good idea to have an option for this at least as an internal option

tangentially related... seems like a PR replacing all instances of /run/wrappers/bin in nixpkgs/nixos with config.security.wrapperDir is a good idea... we might even consider setting security.wrapperDir = "/sbin"; on system-manager 🤷‍♂️

---

To help make modules more portable, is there some attribute that would return /run/current-system/sw in a nixosModule and /run/system-manager on a systemModule? I’d be happy to fix the hardcoding of /run/current-system/sw in nixpkgs if so.

please do, and if you don't mind i would love a ping on that PR

[Meliketoaste]

In nixpkgs they also use environment.pathsToLink this seems relevant but Im dumb.

pathsToLink = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        # Note: We need `/lib' to be among `pathsToLink' for NSS modules
        # to work.
        default = [];
        example = ["/"];
        description = "List of directories to be symlinked in {file}`/run/current-system/sw`.";
};