ctucx.git: nixfiles

configurations/nixos/default: try to keep at least 1GB of disk-space free (nix.settings)

diff --git a/configurations/nixos/default.nix b/configurations/nixos/default.nix
@@ -50,7 +50,13 @@ in {
   nix = {
     channel.enable = false;
 
-    settings.auto-optimise-store = true;
+    settings = {
+      auto-optimise-store = true;
+
+      # Free up to 1GiB whenever there is less than 100MiB left.
+      min-free = toString (100 * 1024 * 1024);
+      max-free = toString (1024 * 1024 * 1024);
+    };
 
     daemonCPUSchedPolicy = lib.mkDefault "idle";
     daemonIOSchedClass   = lib.mkDefault "idle";