feature(boot): attatch /tmp to tmpfs, but keep nix build in /var/tmp

Reviewed-on: #83

modules/nixos/bootloader.nix

@@ -24,6 +24,12 @@
   boot.kernelPackages = pkgs.linuxPackages_latest;
   boot.consoleLogLevel = 2;
 
+  # /tmp in RAM, nix builds go to /var/tmp instead (see settings.nix)
+  boot.tmp = {
+    useTmpfs = true;
+    tmpfsSize = "50%";
+  };
+
   # Add boot-related packages
   environment.systemPackages = with pkgs; [
     efibootmgr

modules/nixos/settings.nix

@@ -27,6 +27,9 @@
     };
   };
 
+  # build on disk, big builds would fill the /tmp tmpfs
+  systemd.services.nix-daemon.environment.TMPDIR = "/var/tmp";
+
   # steam, protonvpn, discord, etc.
   nixpkgs.config.allowUnfree = true;