diff -Nru ubuntu-image-1.4+18.04ubuntu1/debian/changelog ubuntu-image-1.4+18.04ubuntu2/debian/changelog
--- ubuntu-image-1.4+18.04ubuntu1/debian/changelog	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/debian/changelog	2018-08-21 13:25:59.000000000 +0000
@@ -1,3 +1,14 @@
+ubuntu-image (1.4+18.04ubuntu2) bionic; urgency=medium
+
+  * Demote the qemu-user-static dependency to Suggests, modify the code to
+    gracefully handle the lack of qemu binaries for cross-compilation.
+    (LP:1788177)
+  * Add missing information about UBUNTU_IMAGE_QEMU_USER_STATIC_PATH to the
+    manpage.
+  * SRU tracking number LP: #1786229
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Tue, 21 Aug 2018 15:25:59 +0200
+
 ubuntu-image (1.4+18.04ubuntu1) bionic; urgency=medium
 
   * Add support for classic cross-compilation, add qemu-user-static as a
diff -Nru ubuntu-image-1.4+18.04ubuntu1/debian/control ubuntu-image-1.4+18.04ubuntu2/debian/control
--- ubuntu-image-1.4+18.04ubuntu1/debian/control	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/debian/control	2018-08-21 13:25:59.000000000 +0000
@@ -52,9 +52,9 @@
          python3-voluptuous,
          python3-yaml,
          snapd,
-         qemu-user-static,
          ${misc:Depends},
          ${python3:Depends},
+Suggests: qemu-user-static,
 Description: toolkit for building Ubuntu images
  .
  This package contains the ubuntu-image library for Python 3.
diff -Nru ubuntu-image-1.4+18.04ubuntu1/snapcraft.yaml ubuntu-image-1.4+18.04ubuntu2/snapcraft.yaml
--- ubuntu-image-1.4+18.04ubuntu1/snapcraft.yaml	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/snapcraft.yaml	2018-08-21 13:25:59.000000000 +0000
@@ -2,7 +2,7 @@
 summary: Create Ubuntu images
 description: |
   Use this tool to create Ubuntu images.
-version: 1.4+snap1
+version: 1.4+snap4
 grade: stable
 confinement: classic
 
@@ -31,7 +31,6 @@
       - dosfstools
       - e2fsprogs
       - fakeroot
-      - libc6
       - mtools
       - python3-debian
       - python3-git
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/classic_builder.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/classic_builder.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/classic_builder.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/classic_builder.py	2018-08-21 13:25:59.000000000 +0000
@@ -9,7 +9,7 @@
 from tempfile import gettempdir
 from ubuntu_image.common_builder import AbstractImageBuilderState
 from ubuntu_image.helpers import (
-     check_root_privilege, live_build, run)
+     check_root_privilege, get_host_arch, live_build, run)
 from ubuntu_image.parser import (
     BootLoader, FileSystemType, StructureRole)
 
@@ -67,6 +67,9 @@
                 env['EXTRA_PPAS'] = self.args.extra_ppas
             # Only genereate a single rootfs tree for classic image creation.
             env['IMAGEFORMAT'] = 'none'
+            # ensure ARCH is set
+            if self.args.arch is None:
+                env['ARCH'] = get_host_arch()
             live_build(self.unpackdir, env)
         except CalledProcessError:
             if self.args.debug:
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/helpers.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/helpers.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/helpers.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/helpers.py	2018-08-21 13:25:59.000000000 +0000
@@ -175,6 +175,11 @@
                 # Try to guess the qemu-user-static binary name and find it.
                 static = get_qemu_static_for_arch(arch)
                 qemu_path = find_executable(static)
+                if qemu_path is None:
+                    raise DependencyError(
+                        static,
+                        'Use UBUNTU_IMAGE_QEMU_USER_STATIC_PATH in case of '
+                        'non-standard archs or custom paths.')
             config_cmd.extend(['--bootstrap-qemu-arch', arch,
                                '--bootstrap-qemu-static', qemu_path,
                                '--architectures', arch])
@@ -273,3 +278,11 @@
 
     def __init__(self, user_name):
         self.user_name = user_name
+
+
+class DependencyError(ExpectedError):
+    """An optional dependency is missing."""
+
+    def __init__(self, name, additional_info=''):
+        self.name = name
+        self.additional_info = additional_info
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/__main__.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/__main__.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/__main__.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/__main__.py	2018-08-21 13:25:59.000000000 +0000
@@ -11,7 +11,7 @@
 from ubuntu_image.assertion_builder import ModelAssertionBuilder
 from ubuntu_image.classic_builder import ClassicBuilder
 from ubuntu_image.helpers import (
-    DoesNotFit, PrivilegeError, as_size, get_host_arch,
+    DependencyError, DoesNotFit, PrivilegeError, as_size,
     get_host_distro)
 from ubuntu_image.hooks import HookError
 from ubuntu_image.i18n import _
@@ -254,7 +254,7 @@
         help=_("""Distribution name to be specified to livecd-rootfs."""))
     classic_cmd.add_argument(
         '-a', '--arch',
-        default=get_host_arch(), metavar='CPU-ARCHITECTURE',
+        default=None, metavar='CPU-ARCHITECTURE',
         help=_("""CPU architecture to be specified to livecd-rootfs.
         default value is builder arch."""))
     classic_cmd.add_argument(
@@ -361,6 +361,10 @@
                       ' classic image. Please run ubuntu-image as root.'
                       .format(error.user_name))
         return 1
+    except DependencyError as error:
+        _logger.error('Required dependency {} seems to be missing. {}'.format(
+            error.name, error.additional_info))
+        return 1
     except:  # noqa: E722
         _logger.exception('Crash in state machine')
         return 1
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/testing/helpers.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/testing/helpers.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/testing/helpers.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/testing/helpers.py	2018-08-21 13:25:59.000000000 +0000
@@ -91,6 +91,19 @@
             pass
 
 
+class CallLBLeaveATraceClassicBuilder(XXXClassicBuilder):
+    def prepare_gadget_tree(self):
+        # We're skipping the gadget tree build as we're leaving early and will
+        # not use it for the tests.
+        self._next.append(self.prepare_image)
+
+    def load_gadget_yaml(self):
+        # This time we want to call prepare_image for the live-build call but
+        # then finish after leaving a trace
+        with open(os.path.join(self.workdir, 'success'), 'w'):
+            pass
+
+
 class LogCapture:
     def __init__(self):
         self.logs = []
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/tests/test_helpers.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/tests/test_helpers.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/tests/test_helpers.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/tests/test_helpers.py	2018-08-21 13:25:59.000000000 +0000
@@ -13,7 +13,7 @@
 from tempfile import NamedTemporaryFile, TemporaryDirectory
 from types import SimpleNamespace
 from ubuntu_image.helpers import (
-     GiB, MiB, PrivilegeError, as_bool, as_size,
+     DependencyError, GiB, MiB, PrivilegeError, as_bool, as_size,
      check_root_privilege, get_host_arch, get_host_distro,
      get_qemu_static_for_arch, live_build,
      mkfs_ext4, run, snap, sparse_copy)
@@ -433,6 +433,30 @@
                  'PROJECT=ubuntu-server', 'SUITE=xenial', 'ARCH=armhf',
                  'lb', 'build'])
 
+    def test_live_build_cross_build_no_static(self):
+        with ExitStack() as resources:
+            tmpdir = resources.enter_context(TemporaryDirectory())
+            root_dir = os.path.join(tmpdir, 'root_dir')
+            mock = LiveBuildMocker(root_dir)
+            resources.enter_context(LogCapture())
+            resources.enter_context(
+                patch('ubuntu_image.helpers.run', mock.run))
+            resources.enter_context(
+                patch('ubuntu_image.helpers.get_host_arch',
+                      return_value='amd64'))
+            resources.enter_context(
+                patch('ubuntu_image.helpers.find_executable',
+                      return_value=None))
+            env = OrderedDict()
+            env['PROJECT'] = 'ubuntu-server'
+            env['SUITE'] = 'xenial'
+            env['ARCH'] = 'armhf'
+            with self.assertRaises(DependencyError) as cm:
+                live_build(root_dir, env)
+            self.assertEqual(len(mock.call_args_list), 1)
+            self.assertEqual(
+                cm.exception.name, 'qemu-arm-static')
+
     def test_live_build_no_cross_build(self):
         with ExitStack() as resources:
             tmpdir = resources.enter_context(TemporaryDirectory())
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/tests/test_main.py ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/tests/test_main.py
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/tests/test_main.py	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/tests/test_main.py	2018-08-21 13:25:59.000000000 +0000
@@ -16,10 +16,10 @@
 from ubuntu_image.helpers import GiB, MiB
 from ubuntu_image.hooks import supported_hooks
 from ubuntu_image.testing.helpers import (
-    CrashingModelAssertionBuilder, DoNothingBuilder,
-    EarlyExitLeaveATraceAssertionBuilder, EarlyExitLeaveATraceClassicBuilder,
-    EarlyExitModelAssertionBuilder, LogCapture, XXXModelAssertionBuilder,
-    envar)
+    CallLBLeaveATraceClassicBuilder, CrashingModelAssertionBuilder,
+    DoNothingBuilder, EarlyExitLeaveATraceAssertionBuilder,
+    EarlyExitLeaveATraceClassicBuilder, EarlyExitModelAssertionBuilder,
+    LogCapture, XXXModelAssertionBuilder, envar)
 from ubuntu_image.testing.nose import NosePlugin
 from unittest import TestCase, skipIf
 from unittest.mock import call, patch
@@ -615,6 +615,45 @@
             call('Current user(test) does not have root privilege to build '
                  'classic image. Please run ubuntu-image as root.'))
 
+    def test_classic_cross_build_no_static(self):
+        # We need to check that a DependencyError is raised when
+        # find_executable does not find the qemu-<ARCH>-static binary in
+        # PATH (and no path env is set)
+        workdir = self._resources.enter_context(TemporaryDirectory())
+        livecd_rootfs = self._resources.enter_context(TemporaryDirectory())
+        auto = os.path.join(livecd_rootfs, 'auto')
+        os.mkdir(auto)
+        self._resources.enter_context(patch(
+            'ubuntu_image.__main__.ClassicBuilder',
+            CallLBLeaveATraceClassicBuilder))
+        self._resources.enter_context(
+            envar('UBUNTU_IMAGE_LIVECD_ROOTFS_AUTO_PATH', auto))
+        self._resources.enter_context(
+            patch('ubuntu_image.helpers.run', return_value=None))
+        self._resources.enter_context(
+            patch('ubuntu_image.helpers.find_executable', return_value=None))
+        self._resources.enter_context(
+            patch('ubuntu_image.helpers.get_host_arch',
+                  return_value='amd64'))
+        self._resources.enter_context(
+            patch('ubuntu_image.__main__.get_host_distro',
+                  return_value='bionic'))
+        self._resources.enter_context(
+            patch('ubuntu_image.classic_builder.check_root_privilege',
+                  return_value=None))
+        mock = self._resources.enter_context(patch(
+            'ubuntu_image.__main__._logger.error'))
+        code = main(('classic', '--workdir', workdir,
+                     '--project', 'ubuntu-cpc', '--arch', 'armhf',
+                     self.classic_gadget_tree))
+        self.assertEqual(code, 1)
+        self.assertFalse(os.path.exists(os.path.join(workdir, 'success')))
+        self.assertEqual(
+            mock.call_args_list[-1],
+            call('Required dependency qemu-arm-static seems to be missing. '
+                 'Use UBUNTU_IMAGE_QEMU_USER_STATIC_PATH in case of '
+                 'non-standard archs or custom paths.'))
+
     def test_hook_fired(self):
         # For the purpose of testing, we will be using the post-populate-rootfs
         # hook as we made sure it's still executed as part of of the
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/version.txt ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/version.txt
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu_image/version.txt	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu_image/version.txt	2018-08-21 13:25:59.000000000 +0000
@@ -1 +1 @@
-1.4+18.04ubuntu1
+1.4+18.04ubuntu2
diff -Nru ubuntu-image-1.4+18.04ubuntu1/ubuntu-image.rst ubuntu-image-1.4+18.04ubuntu2/ubuntu-image.rst
--- ubuntu-image-1.4+18.04ubuntu1/ubuntu-image.rst	2018-07-20 14:43:51.000000000 +0000
+++ ubuntu-image-1.4+18.04ubuntu2/ubuntu-image.rst	2018-08-21 13:25:59.000000000 +0000
@@ -266,6 +266,13 @@
     Otherwise it will attempt to localize ``livecd-rootfs`` through a call to
     ``dpkg``.
 
+``UBUNTU_IMAGE_QEMU_USER_STATIC_PATH``
+    In case of classic image cross-compilation for a different architecture,
+    ``ubuntu-image`` will attempt to use the qemu-user-static emulator with
+    ``live-build``.  If set, ``ubuntu-image`` will use the selected path for
+    the cross-compilation.  Otherwise it will attempt to find a matching
+    emulator binary in the current ``$PATH``.
+
 There are a few other environment variables used for building and testing
 only.