+## Pre-release
+
+In this example we will clone a pending PR, build a pre-release, then
+check this pre-release for regressions.
+
+We need to build a release tarball in order to run our tests. The
+release tarball contains both an installer and the required binary
+packages to install and run NixOS.
+
+```
+git clone git@github.com:contributor/nix.git --branch XXX
+cd nix && nix-build release.nix -A binaryTarball.x86_64-linux
+```
+
+
+If the build finishes successfully it should print the location of the
+tarball on the last line. Unpack the tarball and start a simple
+webserver to serve these data during our tests.
+
+```
+tar axf nix-2.3pre6621_92d08c0-x86_64-linux.tar.bz2 -C /tmp/
+cd /tmp/nix-2.3pre6621_92d08c0-x86_64-linux && python -m SimpleHTTPServer
+# Confirm the URL is working
+curl --output /dev/null --silent --head --fail \
+    "http://localhost:8000/install" || echo No Page Found!
+```
+
+Update `installUrl` in matrix.nix to point to our URL
+
+```
+  installScripts = let
+    installUrls = {
+      pre =  "http://localhost:8000/install";
+      stable = "https://nixos.org/nix/install";
+      "2.0.4" = "https://nixos.org/releases/nix/nix-2.0.4/install";
+    };
+    installUrl = installUrls.pre;
+```
+
+ XXX Write Me
+
+  1. Tweak test script to run preflight checks before creating a release tarball,
+    this step is very long so we want to get it right the first time. Suggest alternate methods
+   for saving time when building the tarball.
+ 
+ 2. Have the test script install the following packages (assume there is no bootstrap for using nixpkgs?) in which case these need to be installed with your distro's package manger.

+wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -
+wget -q https://www.virtualbox.org/download/oracle_vbox.asc -O- | sudo apt-key add -
+sudo add-apt-repository "deb http://download.virtualbox.org/virtualbox/debian `lsb_release -cs` contrib"
+sudo apt-get update
+sudo apt-get install virtualbox-5.2
+    sudo apt install qemu-kvm libvirt-bin -- why can't we use nixos?
+    sudo apt install vagrant
+    sudo usermod -a -G libvirtd $USER
+
+  3. System set-up requirements
+    i. $USER belongs to libvirtd group
+    ii.  umask is 022
+

diff --git a/matrix.nix b/matrix.nix
index b5cf920..d028da3 100644
--- a/matrix.nix
+++ b/matrix.nix
@@ -1,7 +1,7 @@
 {
   installScripts = let
     installUrls = {
-      pre = "https://nixos.org/releases/nix/nix-2.1pre6385_d16ff76c/install";
+      pre = "http://127.0.0.1:8000/install";
       stable = "https://nixos.org/nix/install";
       "2.0.4" = "https://nixos.org/releases/nix/nix-2.0.4/install";
     };
@@ -194,6 +194,15 @@
       '';
     };
 
+    "ubuntu-16-04-non-standard-umask" = {
+      image = "ubuntu/xenial64";
+      preInstall = ''
+        apt-get update
+        apt-get install -y curl
+        echo "umask 027 >> /etc/profile"
+      '';
+    };
+
     "ubuntu-14-04" = {
       image = "ubuntu/trusty64";
       preInstall = ''