diff -Nru ubiquity-2.21.63.7/debian/changelog ubiquity-2.21.63.9/debian/changelog
--- ubiquity-2.21.63.7/debian/changelog	2018-07-12 23:37:26.000000000 +0200
+++ ubiquity-2.21.63.9/debian/changelog	2018-10-12 15:20:43.000000000 +0200
@@ -1,3 +1,19 @@
+ubiquity (2.21.63.9) xenial; urgency=medium
+
+  * Revert the changes from 2.21.63.8 in favour of the following instead:
+
+  [ Dariusz Gadomski ]
+  * Implement missing reboot and shutdown methods in debconf_ui (LP: #1749289)
+
+ -- Dariusz Gadomski <dariusz.gadomski@canonical.com>  Fri, 12 Oct 2018 15:20:43 +0200
+
+ubiquity (2.21.63.8) xenial; urgency=medium
+
+  [ Dariusz Gadomski ]
+  * Fixes a systemd freeze after cancelling debconf UI. (LP: #1749289)
+
+ -- Dimitri John Ledkov <xnox@ubuntu.com>  Tue, 31 Jul 2018 13:41:52 +0100
+
 ubiquity (2.21.63.7) xenial; urgency=medium
 
   * Automatic update of included source packages: console-setup
diff -Nru ubiquity-2.21.63.7/ubiquity/frontend/debconf_ui.py ubiquity-2.21.63.9/ubiquity/frontend/debconf_ui.py
--- ubiquity-2.21.63.7/ubiquity/frontend/debconf_ui.py	2018-07-12 23:44:29.000000000 +0200
+++ ubiquity-2.21.63.9/ubiquity/frontend/debconf_ui.py	2018-10-12 15:20:27.000000000 +0200
@@ -33,7 +33,7 @@
 
 import debconf
 
-from ubiquity import i18n
+from ubiquity import misc, i18n
 from ubiquity.components import install, plugininstall
 from ubiquity.frontend.base import BaseFrontend, Controller
 from ubiquity.plugin import Plugin
@@ -87,6 +87,12 @@
         if 'DEBIAN_HAS_FRONTEND' not in os.environ:
             BaseFrontend.stop_debconf(self)
 
+    def do_reboot(self):
+        misc.execute_root("reboot")
+
+    def do_shutdown(self):
+        misc.execute_root("poweroff")
+
     def run(self):
         if os.getuid() != 0:
             print(textwrap.fill(