nixos/modules/installer/cd-dvd/channel.nix: pin nixpkgs registry to pkgs.path via boot.postBootCommands

nixos/modules/installer/cd-dvd/channel.nix

@@ -45,6 +45,10 @@ in
         ln -s /nix/var/nix/profiles/per-user/root/channels /root/.nix-defexpr/channels
         mkdir -m 0755 -p /var/lib/nixos
         touch /var/lib/nixos/did-channel-init
+        echo "pinning the nixpkgs registry entry to NixOS/Nixpkgs sources..."
+        ${config.nix.package.out}/bin/nix \
+          --extra-experimental-features 'nix-command flakes' \
+          registry pin nixpkgs ${toString pkgs.path}
       fi
     '';
 }