SelfPrivacy NixOS configuration

This configuration is not self-contained, as it needs to be plugged as an input of a top-level NixOS configuration flake (i.e. https://git.selfprivacy.org/SelfPrivacy/selfprivacy-nixos-template/). This flake outputs the following function:

nixosConfigurations-fun =
  { hardware-configuration # hardware-configuration.nix file
  , deployment             # deployment.nix file
  , userdata               # nix attrset, obtained by fromJSON from userdata.json
  , top-level-flake        # `self`-reference of the top-level flake
  , sp-modules             # flake inputs of sp-modules flake
  }:

which returns one or more attributes, containing NixOS configurations (created with nixpkgs.lib.nixosSystem). (As of 2024-01-10 there is only a single configuration named default.)

updating flake inputs

We have 2 flake inputs:

• nixpkgs
• selfprivacy-api

Both get updated the same ways.

There are 2 methods:

1. specify input name only in a command, relying on URL inside flake.nix
2. specify input name and URL in a command, overriding whatever URL is inside flake.nix for the input to update (override)

In any case a Nix flake input is specified using some special references syntax, including URLs, revisions, etc, described in manual: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#examples. Such reference can be used inside flake.nix or as an argument to nix flake commands. When a new reference is encountered Nix downloads and extracts it to /nix/store.

Before and after running nix flake lock (or nix flake update) commands you would most likely want to list current inputs using nix flake metadata, which are read from flake.lock file. Although, Nix should also print a diff between changed references once changed.

--commit-lock-file option tells Nix commands to do git commit flake.lock automatically, creating a new commit for you.

method 1: update specific input

Example:

$ nix flake lock --update-input nixpkgs
$ nix flake lock --update-input selfprivacy-api

Depending on how "precise" the URL was speficied in flake.nix, with unmodified flake.nix the result might be:

• URL with rev (sha1) parameter => nothing will update (as we're already at exact commit)
• URL with ref (branch) parameter => input will update to the latest commit of the specified branch
• URL without rev nor ref => input will update to the latest commit of a default branch!

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Once Nix 2.19 stabilizes, a different command must be used for updating a single input (recursively), like this:

$ nix flake update nixpkgs

method 2: override specific input

Overriding is more powerful (for non-nested flakes) as it allows to change a flake input reference to anything just in one command (not only update in the bounds of a branch or a repository).

Example:

$ nix flake lock --override-input nixpkgs github:nixos/nixpkgs?ref=nixos-23.11
$ nix flake lock --override-input selfprivacy-api git+https://git.selfprivacy.org/SelfPrivacy/selfprivacy-rest-api.git?ref=flakes

Similarly to update mechanism (described above), depending on the "precision" of an URL, its update scope varies accordingly.

Note, that subsequent calls of nix flake lock --update-input <INPUT> or nix flake update (or nix flake update INPUT by Nix 2.19+) will update the input regardless of the prior override. The information about override is stored only in flake.lock (flake.nix is not altered by Nix).

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Note, that override does not update flake inputs recursively (say, you have a flake nested inside your flake input). For recursive updates only nix flake lock --update-input and nix flake update mechanisms are suitable. However, as of 2024-01-10 none of the SP NixOS configuration inputs contain other flakes, hence override mechanism is fine (don't confuse with top-level flake which has nested inputs).