nixos/cage: init

Add a cage module to nixos. This can be used to make kiosk-style
systems that boot directly to a single application. The user (demo by
default) is automatically logged in by this service and the
program (xterm by default) is automatically started.

This is useful for some embedded, single-user systems where we want
automatic booting. To keep the system secure, the user should have
limited privileges.

Based on the service provided in the Cage wiki here:

https://github.com/Hjdskes/cage/wiki/Starting-Cage-on-boot-with-systemd

Co-Authored-By: Florian Klink <flokli@flokli.de>

2 files changed, 44 insertions, 0 deletions

diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
index 2e547780439..9858113c8be 100644
--- a/nixos/tests/all-tests.nix
+++ b/nixos/tests/all-tests.nix
@@ -39,6 +39,7 @@ in
   buildbot = handleTest ./buildbot.nix {};
   caddy = handleTest ./caddy.nix {};
   cadvisor = handleTestOn ["x86_64-linux"] ./cadvisor.nix {};
+  cage = handleTest ./cage.nix {};
   cassandra = handleTest ./cassandra.nix {};
   ceph-single-node = handleTestOn ["x86_64-linux"] ./ceph-single-node.nix {};
   ceph-multi-node = handleTestOn ["x86_64-linux"] ./ceph-multi-node.nix {};
diff --git a/nixos/tests/cage.nix b/nixos/tests/cage.nix
new file mode 100644
index 00000000000..a6f73e00c06
--- /dev/null
+++ b/nixos/tests/cage.nix
@@ -0,0 +1,43 @@
+import ./make-test-python.nix ({ pkgs, ...} :
+
+{
+  name = "cage";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ matthewbauer flokli ];
+  };
+
+  machine = { ... }:
+
+  {
+    imports = [ ./common/user-account.nix ];
+    services.cage = {
+      enable = true;
+      user = "alice";
+      program = "${pkgs.xterm}/bin/xterm -cm -pc"; # disable color and bold to make OCR easier
+    };
+
+    # this needs a fairly recent kernel, otherwise:
+    #   [backend/drm/util.c:215] Unable to add DRM framebuffer: No such file or directory
+    #   [backend/drm/legacy.c:15] Virtual-1: Failed to set CRTC: No such file or directory
+    #   [backend/drm/util.c:215] Unable to add DRM framebuffer: No such file or directory
+    #   [backend/drm/legacy.c:15] Virtual-1: Failed to set CRTC: No such file or directory
+    #   [backend/drm/drm.c:618] Failed to initialize renderer on connector 'Virtual-1': initial page-flip failed
+    #   [backend/drm/drm.c:701] Failed to initialize renderer for plane
+    boot.kernelPackages = pkgs.linuxPackages_latest;
+
+    virtualisation.memorySize = 1024;
+  };
+
+  enableOCR = true;
+
+  testScript = { nodes, ... }: let
+    user = nodes.machine.config.users.users.alice;
+  in ''
+    with subtest("Wait for cage to boot up"):
+        start_all()
+        machine.wait_for_file("/run/user/${toString user.uid}/wayland-0.lock")
+        machine.wait_until_succeeds("pgrep xterm")
+        machine.wait_for_text("alice@machine")
+        machine.screenshot("screen")
+  '';
+})