nixdots/system/shared/impermanence/root.nix

{ config, lib, ... }: let
  inherit (lib) mkIf mkForce;

  cfgSystem = config.myOptions.system;
  cfg = config.myOptions.system.impermanence.root;
in
{
  config = mkIf cfg.enable {
    users = {
      # This option makes it that users are not mutable outside of our configuration.
      # If you're using root impermanence, this will actually be the case regardless
      # of this setting, however, setting this explicitly is a good idea, because nix
      # will warn us if our users don't have passwords set, preventing lock outs.
      mutableUsers = false;

      # Each existing user needs to have a password file defined here, otherwise
      # they will not be available to login. These password files can be generated with:
      # mkpasswd -m sha-512 > /persist/passwords/myuser
      users = {
        root = {
          hashedPasswordFile = "${cfg.persistentMountPoint}/passwords/root";
        };
        ${cfgSystem.username} = {
          hashedPasswordFile = "${cfg.persistentMountPoint}/passwords/${cfgSystem.username}";
        };
      };
    };

    environment.persistence."${cfg.persistentMountPoint}/system" = {
      hideMounts = true;
      directories = [
        "/etc/nixos" # NixOS configuration source
        "/etc/NetworkManager/system-connections" # saved network connections
        "/var/db/sudo" # keeps track of who got the sudo lecture already
        # "/var/log" # I sometimes use a subvolume for this, added manually if not
        "/var/lib/nixos"
        "/var/lib/bluetooth"
        "/var/lib/systemd/coredump" # captured coredumps 
      ] ++ cfg.extraDirectories;

      files = [
        "/etc/machine-id"
      ] ++ cfg.extraFiles;
    };

    # For some reason, NetworkManager needs this instead of the impermanence mode
    # to not get screwed up
    systemd.tmpfiles.rules = [
      "L /var/lib/NetworkManager/secret_key - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/secret_key"
      "L /var/lib/NetworkManager/seen-bssids - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/seen-bssids"
      "L /var/lib/NetworkManager/timestamps - - - - ${cfg.persistentMountPoint}/system/var/lib/NetworkManager/timestamps"
    ];

    # Define host key paths in the persistent mount point instead of using impermanence for these.
    # This works better, because these keys also get auto-created if they don't already exist.
    services.openssh.hostKeys = mkForce [
      {
        bits = 4096;
        path = "${cfg.persistentMountPoint}/system/etc/ssh/ssh_host_rsa_key";
        type = "rsa";
      }
      {
        bits = 4096;
        path = "${cfg.persistentMountPoint}/system/etc/ssh/ssh_host_ed25519_key";
        type = "ed25519";
      }
    ];
  };
}