Mount /tmp from RAM

modules/nixos/linux-headless.nix

@@ -3,7 +3,7 @@
   ...
 }:
 {
-  # Create /etc/zshrc that loads the nix-darwin environment.
+  # Create /etc/zshrc that loads the nix environment.
   programs.zsh.enable = true;
   security.sudo.wheelNeedsPassword = false;
 

modules/nixos/linux-lxc.nix

@@ -1,6 +1,7 @@
 {
   modulesPath,
   pkgs,
+  lib,
   ...
 }:
 {
@@ -73,4 +74,7 @@
     capabilities = "cap_net_raw+p";
     source = "${pkgs.iputils.out}/bin/ping";
   };
+
+  # Our VMs usually have sufficient RAM, prefer to extend SSD lifetime.
+  boot.tmp.useTmpfs = lib.mkDefault true;
 }