impermanence

flake.nix

@@ -12,6 +12,10 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
     nix-flatpak.url = "github:gmodena/nix-flatpak/?ref=latest";
+    impermanence = {
+      url = "github:nix-community/impermanence";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     lix-module.url = "git+https://git.lix.systems/lix-project/nixos-module?ref=release-2.93";
     lix-module.inputs.nixpkgs.follows = "nixpkgs";
     lanzaboote.url = "github:nix-community/lanzaboote";

modules/profile/nanuqsaurus.nix

@@ -5,6 +5,7 @@
     inputs.lix-module.nixosModules.lixFromNixpkgs
     inputs.nix-index-database.nixosModules.nix-index
     inputs.nix-flatpak.nixosModules.nix-flatpak
+    inputs.impermanence.nixosModules.impermanence
     ../system/flatpak.nix
     ../system/base.nix
     ../system/packages.nix
@@ -13,6 +14,7 @@
     ../system/home-manager-skel.nix
     ../system/fonts.nix
     ../system/printer.nix
+    ../system/impermanence.nix
     ../desktop/desktop-entries.nix
     ../desktop/file-manager.nix
     ../desktop/gnome-minimal.nix

modules/system/disko-btrfs.nix

@@ -27,6 +27,7 @@
             content = {
               type = "btrfs";
               extraArgs = [ "-f" ];
+              label = "nixos";
               subvolumes = {
                 root = {
                   mountpoint = "/";
@@ -48,6 +49,13 @@
                     "compress=zstd"
                   ];
                 };
+
+                persist = {
+                  mountpoint = "/persist";
+                  mountOptions = [
+                    "compress=zstd"
+                  ];
+                };
               };
             };
           };

modules/system/impermanence.nix

@@ -0,0 +1,46 @@
+{ config, lib, ... }:
+
+{
+  config = lib.mkIf (
+    (config.fileSystems ? "/persist")
+    && (config.fileSystems."/persist".fsType or "" == "btrfs")
+  ) {
+    boot.initrd.supportedFilesystems = [ "btrfs" ];
+
+    boot.initrd.postDeviceCommands = lib.mkAfter ''
+      mkdir -p /mnt
+      mount -t btrfs -o subvol=/ /dev/disk/by-label/nixos /mnt
+
+      if [ ! -d /mnt/root-blank ]; then
+        btrfs subvolume snapshot -r /mnt/root /mnt/root-blank
+      fi
+
+      if [ -d /mnt/root ]; then
+        btrfs subvolume delete /mnt/root
+      fi
+
+      btrfs subvolume snapshot /mnt/root-blank /mnt/root
+      umount /mnt
+    '';
+
+    fileSystems."/persist".neededForBoot = true;
+
+    environment.persistence."/persist" = {
+      hideMounts = true;
+      directories = [
+        "/etc/nixos"
+        "/etc/ssh"
+        "/etc/cups"
+        "/var/lib/cups"
+        "/var/lib/libvirt"
+        "/var/lib/secureboot"
+        "/var/lib/tailscale"
+        "/var/lib/systemd"
+        "/var/lib/nixos"
+      ];
+      files = [
+        "/etc/machine-id"
+      ];
+    };
+  };
+}