use nixpkgs.json

NIXPKGS_VERSION

@@ -1 +0,0 @@
-22a606e20d662e2575552ab9b5e7c31aa8331e0e

configs/shells.nix

@@ -80,13 +80,15 @@ in {
 
       niveum-deploy() {
         for system in "$@"; do
-          eval $(nix-build ~niveum/deploy.nix -A "$system")
+          eval $(nix-build ~niveum/deploy.nix -A "$system") &
         done
       }
 
       niveum-update() {
-        cd /var/src/nixpkgs
-        git rev-parse origin/nixos-18.09 > ~niveum/NIXPKGS_VERSION
+        nix-prefetch-git \                                                                                                                                                              ~master
+          --url https://github.com/NixOS/nixpkgs-channels \
+          --rev refs/heads/nixos-18.09 \
+          > ~niveum/nixpkgs.json
       }
     '';
     promptInit = ''

deploy.nix

@@ -8,12 +8,12 @@ let
   };
   lib = import "${krops}/lib";
   pkgs = import "${krops}/pkgs" {};
+  importJson = (import <nixpkgs> {}).lib.importJSON;
 
   source = name: path: lib.evalSource [{
     nixpkgs.git = {
       url = https://github.com/NixOS/nixpkgs-channels;
-      # ref = "6a3f5bcb061e1822f50e299f5616a0731636e4e7"; # 18.09
-      ref = builtins.readFile ./NIXPKGS_VERSION;
+      ref = (importJson ./nixpkgs.json).rev;
     };
     nix-writers.git = {
       url = https://cgit.krebsco.de/nix-writers/;

nixpkgs.json

@@ -0,0 +1,7 @@
+{
+  "url": "https://github.com/NixOS/nixpkgs-channels",
+  "rev": "46d3867a08a9206685e2b6a8e19f5ad9f6ab4b39",
+  "date": "2019-04-11T01:41:16+03:00",
+  "sha256": "16nryjvfaw2dq55yp34hcw5bz8nlidhdi3yvr2ilr7lrlm4k54p1",
+  "fetchSubmodules": false
+}