Merge pull request #47228 from obsidiansystems/nix-2.0-19.03

release-notes/19.03: add release notes for nix 2.0 requirement bump

nixos/doc/manual/release-notes/rl-1903.xml

@@ -42,6 +42,66 @@
   </itemizedlist>
  </section>
 
+ <section xmlns="http://docbook.org/ns/docbook"
+         xmlns:xlink="http://www.w3.org/1999/xlink"
+         xmlns:xi="http://www.w3.org/2001/XInclude"
+         version="5.0"
+         xml:id="sec-release-18.09-incompatibilities">
+  <title>Backward Incompatibilities</title>
+
+  <para>
+   When upgrading from a previous release, please be aware of the following
+   incompatible changes:
+  </para>
+
+  <itemizedlist>
+   <listitem>
+    <para>
+     The minimum version of Nix required to evaluate Nixpkgs is now 2.0.
+    </para>
+    <itemizedlist>
+     <listitem>
+      <para>
+       For users of NixOS 18.03 and 19.03, NixOS defaults to Nix 2.0, but
+       supports using Nix 1.11 by setting <literal>nix.package =
+       pkgs.nix1;</literal>. If this option is set to a Nix 1.11 package, you
+       will need to either unset the option or upgrade it to Nix 2.0.
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       For users of NixOS 17.09, you will first need to upgrade Nix by setting
+       <literal>nix.package = pkgs.nixStable2;</literal> and run
+       <command>nixos-rebuild switch</command> as the <literal>root</literal>
+       user.
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       For users of a daemon-less Nix installation on Linux or macOS, you can
+       upgrade Nix by running <command>curl https://nixos.org/nix/install |
+       sh</command>, or prior to doing a channel update, running
+       <command>nix-env -iA nix</command>.
+      </para>
+      <para>
+       If you have already run a channel update and Nix is no longer able to
+       evaluate Nixpkgs, the error message printed should provide adequate
+       directions for upgrading Nix.
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       For users of the Nix daemon on macOS, you can upgrade Nix by running
+       <command>sudo -i sh -c 'nix-channel --update &amp;&amp; nix-env -iA
+       nixpkgs.nix'; sudo launchctl stop org.nixos.nix-daemon; sudo launchctl
+       start org.nixos.nix-daemon</command>.
+      </para>
+     </listitem>
+    </itemizedlist>
+   </listitem>
+  </itemizedlist>
+ </section>
+
  <section xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"