improve system activation

2 files changed, 17 insertions, 0 deletions

diff --git a/modules/system/activation-scripts.nix b/modules/system/activation-scripts.nix
index fda882f..f32e1de 100644
--- a/modules/system/activation-scripts.nix
+++ b/modules/system/activation-scripts.nix
@@ -34,6 +34,19 @@ in
 
   config = {
 
+    system.build.activate = pkgs.writeText "activate-system" ''
+      #! ${pkgs.stdenv.shell}
+
+      # Make this configuration the current configuration.
+      # The readlink is there to ensure that when $systemConfig = /system
+      # (which is a symlink to the store), /run/current-system is still
+      # used as a garbage collection root.
+      ln -sfn $(cat /nix/var/nix/profiles/system/systemConfig) /run/current-system
+
+      # Prevent the current configuration from being garbage-collected.
+      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+    '';
+
     system.activationScripts.script.text = ''
       #! ${pkgs.stdenv.shell}
 
diff --git a/modules/system/default.nix b/modules/system/default.nix
index 7689e42..9cf190e 100644
--- a/modules/system/default.nix
+++ b/modules/system/default.nix
@@ -46,6 +46,8 @@ in
       buildCommand = ''
         mkdir $out
 
+        systemConfig=$out
+
         ln -s ${cfg.build.etc}/etc $out/etc
         ln -s ${cfg.path} $out/sw
 
@@ -57,6 +59,8 @@ in
         chmod u+x $out/activate
         unset activationScript
 
+        echo -n "$systemConfig" > $out/systemConfig
+
         echo -n "$nixdarwinLabel" > $out/nixdarwin-version
         echo -n "$system" > $out/system
       '';