refactor: make system.stateVersion common across all hosts.

otherwise it's hairy to share nixos configs/modules between them

note that this alters the stateVersion for desko/lappy/rescue, but unlikely to matter

hosts/by-name/desko/default.nix

@@ -52,7 +52,4 @@
     # TODO: ALLOW_USERS doesn't seem to work. still need `sudo snapper -c nix list`
     ALLOW_USERS = [ "colin" ];
   };
-
-  # docs: https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion
-  system.stateVersion = "21.05";
 }

hosts/by-name/lappy/default.nix

@@ -34,7 +34,4 @@
     SUBVOLUME = "/nix";
     ALLOW_USERS = [ "colin" ];
   };
-
-  # docs: https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion
-  system.stateVersion = "21.05";
 }

hosts/by-name/moby/default.nix

@@ -64,6 +64,4 @@
   # /boot space is at a premium. default was 20.
   # even 10 can be too much
   boot.loader.generic-extlinux-compatible.configurationLimit = 8;
-
-  system.stateVersion = "21.11";
 }

hosts/by-name/rescue/default.nix

@@ -12,7 +12,4 @@
   # auto-login at shell
   services.getty.autologinUser = "colin";
   # users.users.colin.initialPassword = "colin";
-
-  # docs: https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion
-  system.stateVersion = "21.05";
 }

hosts/by-name/servo/default.nix

@@ -46,13 +46,5 @@
   boot.kernel.sysctl = {
     "net.core.rmem_max" = 4194304;  # 4MB
   };
-
-  # This value determines the NixOS release from which the default
-  # settings for stateful data, like file locations and database versions
-  # on your system were taken. It‘s perfectly fine and recommended to leave
-  # this value at the release version of the first install of this system.
-  # Before changing this value read the documentation for this option
-  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
-  system.stateVersion = "21.11";
 }
 

hosts/common/default.nix

@@ -20,6 +20,11 @@
     ./users
   ];
 
+
+  # docs: https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion
+  # this affects where nixos modules look for stateful data which might have been migrated across releases.
+  system.stateVersion = "21.11";
+
   sane.nixcache.enable-trusted-keys = true;
   sane.nixcache.enable = lib.mkDefault true;
   sane.persist.enable = lib.mkDefault true;