Update for 26.05/nixos-unstable

final/configuration.nix

@@ -19,6 +19,8 @@
     extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
   };
 
+  # if you get an error about postDeviceCommands no longer available (26.05 or
+  # unstable), read further
   boot.initrd.postDeviceCommands = lib.mkAfter ''
     mkdir /btrfs_tmp
     mount /dev/root_vg/root /btrfs_tmp
@@ -43,6 +45,50 @@
     btrfs subvolume create /btrfs_tmp/root
     umount /btrfs_tmp
   '';
+  # only uncomment this if you are on 26.05 or nixos-unstable, and remove the previous block
+  # boot.initrd.systemd = {
+  #   initrdBin = with pkgs; [
+  #     btrfs-progs
+  #     coreutils
+  #     util-linux
+  #     findutils
+  #   ];
+  #
+  #   services.prune-subvolumes = {
+  #     requiredBy = [ "initrd.target" ];
+  #     before = [ "local-fs-pre.target" ];
+  #     after = [
+  #       "initrd-root-device.target"
+  #       "systemd-hibernate-resume.service"
+  #     ];
+  #     unitConfig.DefaultDependencies = false;
+  #     serviceConfig.Type = "oneshot";
+  #     script = ''
+  #       mkdir /btrfs_tmp
+  #       mount /dev/mapper/root_vg-root /btrfs_tmp
+  #       if [[ -e /btrfs_tmp/root ]]; then
+  #         mkdir -p /btrfs_tmp/old_roots
+  #         timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/root)" "+%Y-%m-%-d_%H:%M:%S")
+  #         mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
+  #       fi
+  #
+  #       delete_subvolume_recursively() {
+  #         IFS=$'\n'
+  #         for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+  #           delete_subvolume_recursively "/btrfs_tmp/$i"
+  #         done
+  #         btrfs subvolume delete "$1"
+  #       }
+  #
+  #       for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
+  #         delete_subvolume_recursively "$i"
+  #       done
+  #
+  #       btrfs subvolume create /btrfs_tmp/root
+  #       umount /btrfs_tmp
+  #     '';
+  #   };
+  # };
 
   fileSystems."/persist".neededForBoot = true;
   environment.persistence."/persist/system" = {