nixos: Switch to default systemd-nspawn behaviour

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -542,6 +542,15 @@
           <literal>~/.local/share/polymc/polymc.cfg</literal>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <literal>systemd-nspawn@.service</literal> settings have been
+          reverted to the default systemd behaviour. User namespaces are
+          now activated by default. If you want to keep running nspawn
+          containers without user namespaces you need to set
+          <literal>systemd.nspawn.&lt;name&gt;.execConfig.PrivateUsers = false</literal>
+        </para>
+      </listitem>
       <listitem>
         <para>
           The terraform 0.12 compatibility has been removed and the

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -174,6 +174,7 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - MultiMC has been replaced with the fork PolyMC due to upstream developers being hostile to 3rd party package maintainers. PolyMC removes all MultiMC branding and is aimed at providing proper 3rd party packages like the one contained in Nixpkgs. This change affects the data folder where game instances and other save and configuration files are stored. Users with existing installations should rename `~/.local/share/multimc` to `~/.local/share/polymc`. The main config file's path has also moved from `~/.local/share/multimc/multimc.cfg` to `~/.local/share/polymc/polymc.cfg`.
 
+- `systemd-nspawn@.service` settings have been reverted to the default systemd behaviour. User namespaces are now activated by default. If you want to keep running nspawn containers without user namespaces you need to set `systemd.nspawn.<name>.execConfig.PrivateUsers = false`
 
 - The terraform 0.12 compatibility has been removed and the `terraform.withPlugins` and `terraform-providers.mkProvider` implementations simplified. Providers now need to be stored under
 `$out/libexec/terraform-providers/<registry>/<owner>/<name>/<version>/<os>_<arch>/terraform-provider-<name>_v<version>` (which mkProvider does).

nixos/modules/system/boot/systemd-nspawn.nix

@@ -120,14 +120,6 @@ in {
         })
         {
           systemd.targets.multi-user.wants = [ "machines.target" ];
-
-          # Workaround for https://github.com/NixOS/nixpkgs/pull/67232#issuecomment-531315437 and https://github.com/systemd/systemd/issues/13622
-          # Once systemd fixes this upstream, we can re-enable -U
-          systemd.services."systemd-nspawn@".serviceConfig.ExecStart = [
-            ""  # deliberately empty. signals systemd to override the ExecStart
-            # Only difference between upstream is that we do not pass the -U flag
-            "${config.systemd.package}/bin/systemd-nspawn --quiet --keep-unit --boot --link-journal=try-guest --network-veth --settings=override --machine=%i"
-          ];
         }
       ];
 }

nixos/tests/all-tests.nix

@@ -498,6 +498,7 @@ in
   systemd-confinement = handleTest ./systemd-confinement.nix {};
   systemd-cryptenroll = handleTest ./systemd-cryptenroll.nix {};
   systemd-journal = handleTest ./systemd-journal.nix {};
+  systemd-machinectl = handleTest ./systemd-machinectl.nix {};
   systemd-networkd = handleTest ./systemd-networkd.nix {};
   systemd-networkd-dhcpserver = handleTest ./systemd-networkd-dhcpserver.nix {};
   systemd-networkd-dhcpserver-static-leases = handleTest ./systemd-networkd-dhcpserver-static-leases.nix {};

nixos/tests/systemd-machinectl.nix

@@ -0,0 +1,85 @@
+import ./make-test-python.nix (
+  let
+
+    container = {
+      # We re-use the NixOS container option ...
+      boot.isContainer = true;
+      # ... and revert unwanted defaults
+      networking.useHostResolvConf = false;
+
+      # use networkd to obtain systemd network setup
+      networking.useNetworkd = true;
+      networking.useDHCP = false;
+
+      # systemd-nspawn expects /sbin/init
+      boot.loader.initScript.enable = true;
+
+      imports = [ ../modules/profiles/minimal.nix ];
+    };
+
+    containerSystem = (import ../lib/eval-config.nix {
+      modules = [ container ];
+    }).config.system.build.toplevel;
+
+    containerName = "container";
+    containerRoot = "/var/lib/machines/${containerName}";
+
+  in
+  {
+    name = "systemd-machinectl";
+
+    machine = { lib, ... }: {
+      # use networkd to obtain systemd network setup
+      networking.useNetworkd = true;
+      networking.useDHCP = false;
+      services.resolved.enable = false;
+
+      # open DHCP server on interface to container
+      networking.firewall.trustedInterfaces = [ "ve-+" ];
+
+      # do not try to access cache.nixos.org
+      nix.settings.substituters = lib.mkForce [ ];
+
+      virtualisation.additionalPaths = [ containerSystem ];
+    };
+
+    testScript = ''
+      start_all()
+      machine.wait_for_unit("default.target");
+
+      # Install container
+      machine.succeed("mkdir -p ${containerRoot}");
+      # Workaround for nixos-install
+      machine.succeed("chmod o+rx /var/lib/machines");
+      machine.succeed("nixos-install --root ${containerRoot} --system ${containerSystem} --no-channel-copy --no-root-passwd");
+
+      # Allow systemd-nspawn to apply user namespace on immutable files
+      machine.succeed("chattr -i ${containerRoot}/var/empty");
+
+      # Test machinectl start
+      machine.succeed("machinectl start ${containerName}");
+      machine.wait_until_succeeds("systemctl -M ${containerName} is-active default.target");
+
+      # Test systemd-nspawn network configuration
+      machine.succeed("ping -n -c 1 ${containerName}");
+
+      # Test systemd-nspawn uses a user namespace
+      machine.succeed("test `stat ${containerRoot}/var/empty -c %u%g` != 00");
+
+      # Test systemd-nspawn reboot
+      machine.succeed("machinectl shell ${containerName} /run/current-system/sw/bin/reboot");
+      machine.wait_until_succeeds("systemctl -M ${containerName} is-active default.target");
+
+      # Test machinectl reboot
+      machine.succeed("machinectl reboot ${containerName}");
+      machine.wait_until_succeeds("systemctl -M ${containerName} is-active default.target");
+
+      # Test machinectl stop
+      machine.succeed("machinectl stop ${containerName}");
+
+      # Show to to delete the container
+      machine.succeed("chattr -i ${containerRoot}/var/empty");
+      machine.succeed("rm -rf ${containerRoot}");
+    '';
+  }
+)