(untested) config for stinky and diff script.

common/consul.nix

@@ -27,7 +27,7 @@ in
     };
     };
 
-    environment.persistence."/persist".directories = [ "/var/lib/consul" ];
+    environment.persistence.${config.custom.impermanence.persistPath}.directories = [ "/var/lib/consul" ];
 
     networking.firewall = {
       allowedTCPPorts = [

common/ethereum.nix

@@ -12,7 +12,7 @@
       checkpoint-sync-url = "https://beaconstate.info";
     };
   };
-  environment.persistence."/persist".directories = [
+  environment.persistence.${config.custom.impermanence.persistPath}.directories = [
     "/var/lib/private/lighthouse-mainnet"
   ];
 }

common/global/default.nix

@@ -5,6 +5,7 @@
     ./console.nix
     ./cpufreq.nix
     ./flakes.nix
+    ./impermanence-options.nix
     ./kernel.nix
     ./locale.nix
     ./network.nix

common/global/impermanence-options.nix

@@ -0,0 +1,14 @@
+{
+  lib,
+  ...
+}:
+{
+  # Define impermanence options that need to be available to all modules
+  # The actual impermanence implementation is in common/impermanence.nix or common/impermanence-tmpfs.nix
+
+  options.custom.impermanence.persistPath = lib.mkOption {
+    type = lib.types.str;
+    default = "/persist";
+    description = "Path where persistent data is stored (e.g., /persist for btrfs, /nix/persist for tmpfs)";
+  };
+}

common/global/network.nix

@@ -1,4 +1,4 @@
-{ lib, ... }:
+{ lib, config, ... }:
 {
   networking = {
     useDHCP = true;
@@ -10,7 +10,7 @@
     '';
   };
 
-  environment.persistence."/persist" = {
+  environment.persistence.${config.custom.impermanence.persistPath} = {
     directories = [ "/var/db/dhcpcd" ];
   };
 }

common/global/tailscale.nix

@@ -22,6 +22,6 @@ in
   config = mkIf cfg.enable {
     services.tailscaleAutoconnect.enable = true;
     services.tailscale.package = pkgs.unstable.tailscale;
-    environment.persistence."/persist".directories = [ "/var/lib/tailscale" ];
+    environment.persistence.${config.custom.impermanence.persistPath}.directories = [ "/var/lib/tailscale" ];
   };
 }

common/impermanence-common.nix

@@ -0,0 +1,30 @@
+{
+  lib,
+  config,
+  ...
+}:
+{
+  # Common impermanence configuration shared by both btrfs and tmpfs variants
+  # This module should be imported by impermanence.nix or impermanence-tmpfs.nix
+  # The option custom.impermanence.persistPath is defined in common/global/impermanence-options.nix
+
+  environment.persistence.${config.custom.impermanence.persistPath} = {
+    directories = [
+      "/var/lib/nixos"
+      "/home"
+    ];
+    files = [
+      "/etc/machine-id"
+      "/etc/ssh/ssh_host_ed25519_key"
+      "/etc/ssh/ssh_host_ed25519_key.pub"
+      "/etc/ssh/ssh_host_rsa_key"
+      "/etc/ssh/ssh_host_rsa_key.pub"
+    ];
+  };
+
+  users.mutableUsers = false;
+
+  security.sudo.extraConfig = ''
+    Defaults lecture = never
+  '';
+}

common/impermanence-tmpfs.nix

@@ -0,0 +1,30 @@
+{
+  lib,
+  config,
+  ...
+}:
+{
+  # Impermanence configuration for tmpfs root filesystem
+  # Used for systems with tmpfs root (e.g., Raspberry Pi with SD card)
+  # Root is in-memory and wiped on every boot
+  # Persistent data is stored in /nix/persist (directory on the /nix partition)
+
+  # Import common impermanence configuration
+  imports = [ ./impermanence-common.nix ];
+
+  config = {
+    # Use /nix/persist for tmpfs-based impermanence
+    custom.impermanence.persistPath = "/nix/persist";
+
+    # tmpfs root filesystem
+    fileSystems."/" = {
+      device = "none";
+      fsType = "tmpfs";
+      options = [
+        "defaults"
+        "size=2G"
+        "mode=755"
+      ];
+    };
+  };
+}

common/impermanence.nix

@@ -1,6 +1,5 @@
 {
   pkgs,
-  inputs,
   lib,
   config,
   ...
@@ -9,31 +8,22 @@ let
   cfg = config.custom.impermanence;
 in
 {
+  # Import common impermanence configuration
+  imports = [ ./impermanence-common.nix ];
+
   options.custom.impermanence = {
     enable = lib.mkOption {
       type = lib.types.bool;
       default = true;
-      description = "Enable impermanent root fs";
+      description = "Enable impermanent root fs with btrfs subvolume rollback";
     };
   };
 
   config = lib.mkIf cfg.enable {
-    environment.persistence = {
-      "/persist" = {
-        directories = [
-          "/var/lib/nixos"
-          "/home"
-        ];
-        files = [
-          "/etc/machine-id"
-          "/etc/ssh/ssh_host_ed25519_key"
-          "/etc/ssh/ssh_host_ed25519_key.pub"
-          "/etc/ssh/ssh_host_rsa_key"
-          "/etc/ssh/ssh_host_rsa_key.pub"
-        ];
-      };
-    };
+    # Use /persist for btrfs-based impermanence
+    custom.impermanence.persistPath = "/persist";
 
+    # Btrfs-specific filesystem options
     fileSystems."/".options = [
       "compress=zstd"
       "noatime"
@@ -53,17 +43,7 @@ in
     ];
     fileSystems."/var/log".neededForBoot = true;
 
-    users.mutableUsers = false;
-
-    # rollback results in sudo lectures after each reboot
-    security.sudo.extraConfig = ''
-      Defaults lecture = never
-    '';
-
-    # needed for allowOther in the home-manager impermanence config
-    programs.fuse.userAllowOther = true;
-
-    # reset / at each boot
+    # Btrfs subvolume rollback at each boot
     # Note `lib.mkBefore` is used instead of `lib.mkAfter` here.
     boot.initrd.postDeviceCommands = pkgs.lib.mkBefore ''
       mkdir /mnt

common/nfs-services-server.nix

@@ -24,7 +24,7 @@ in
 
   config = lib.mkIf cfg.enable {
     # Persist root SSH directory for replication key
-    environment.persistence."/persist" = {
+    environment.persistence.${config.custom.impermanence.persistPath} = {
       directories = [
         "/root/.ssh"
       ];

common/nomad.nix

@@ -150,7 +150,7 @@ in
       plugin.raw_exec.config.enabled = true;
     };
 
-    environment.persistence."/persist".directories = [
+    environment.persistence.${config.custom.impermanence.persistPath}.directories = [
       "/var/lib/docker"
       "/var/lib/nomad"
     ];