datetime: Handle timesyncd service runs conditionally

systemd-timesyncd service does not run if we have another NTP daemon installed
or FreedomBox runs inside a container where the host manages the time. In this
case, make the application as unmanaged - app can't be disabled, no app
diagnostics is shown and enable/disable functional tests are skipped.

Closes #1616

Tests performed:
- Run FreedomBox inside a KVM virtualization module, check that
  systemd-timesyncd is running, datetime app can be disabled and all
  diagnostics and date_and_time functional tests pass.
- Run FreedomBox inside a systemd-nspawn container, check that
  systemd-timesyncd is not running, datetime app can't be disabled,
  the diagnostics button is not shown and two date_and_time functional tests
  are skipped.

Signed-off-by: Veiko Aasa <veiko17@disroot.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

functional_tests/features/date_and_time.feature

@@ -8,12 +8,14 @@ Background:
   Given I'm a logged in user
 
 Scenario: Disable network time application
-  Given the network time application is enabled
+  Given the network time application can be disabled
+  And the network time application is enabled
   When I disable the network time application
   Then the network time service should not be running
 
 Scenario: Enable network time application
-  Given the network time application is disabled
+  Given the network time application can be disabled
+  And the network time application is disabled
   When I enable the network time application
   Then the network time service should be running
 

functional_tests/step_definitions/application.py

@@ -33,6 +33,12 @@ def ntp_is_disabled(session_browser):
     application.disable(session_browser, 'ntp')
 
 
+@given(parsers.parse('the network time application can be disabled'))
+def ntp_can_be_disabled(session_browser):
+    if not application.can_be_disabled(session_browser, 'ntp'):
+        pytest.skip(f'network time application can\'t be disabled')
+
+
 @when(parsers.parse('I set the time zone to {time_zone:S}'))
 def time_zone_set(session_browser, time_zone):
     application.time_zone_set(session_browser, time_zone)

functional_tests/support/application.py

@@ -121,6 +121,13 @@ def disable(browser, app_name):
     _change_app_status(browser, app_name, 'disabled')
 
 
+def can_be_disabled(browser, app_name):
+    """Return whether the application can be disabled."""
+    interface.nav_to_module(browser, get_app_module(app_name))
+    button = browser.find_by_css('button[name="app_enable_disable_button"]')
+    return bool(button)
+
+
 def wait_for_config_update(browser, app_name):
     while browser.is_element_present_by_css('.running-status.loading'):
         sleep(0.1)

plinth/modules/datetime/__init__.py

@@ -29,11 +29,13 @@ _description = [
 app = None
 
 
-class DateTimeApp(app_module.App):
-    """FreedomBox app for date and time."""
+class UnmanagedDateTimeApp(app_module.App):
+    """FreedomBox app for date and time if time syncronization is unmanaged."""
 
     app_id = 'datetime'
 
+    can_be_disabled = False
+
     def __init__(self):
         """Create components for the app."""
         super().__init__()
@@ -48,6 +50,16 @@ class DateTimeApp(app_module.App):
                               'datetime:index', parent_url_name='system')
         self.add(menu_item)
 
+
+class ManagedDateTimeApp(UnmanagedDateTimeApp):
+    """FreedomBox app for date and time if time syncronization is managed."""
+
+    can_be_disabled = True
+
+    def __init__(self):
+        """Create components for the app."""
+        super().__init__()
+
         daemon = Daemon('daemon-datetime', managed_services[0])
         self.add(daemon)
 
@@ -61,7 +73,12 @@ class DateTimeApp(app_module.App):
 def init():
     """Initialize the date/time module."""
     global app
-    app = DateTimeApp()
+
+    if _is_time_managed():
+        app = ManagedDateTimeApp()
+    else:
+        app = UnmanagedDateTimeApp()
+
     if app.is_enabled():
         app.set_enabled(True)
 
@@ -83,3 +100,17 @@ def _diagnose_time_synchronized():
         pass
 
     return [_('Time synchronized to NTP server'), result]
+
+
+def _is_time_managed():
+    """Check whether time should be syncronized by the systemd-timesyncd.
+
+    systemd-timesyncd does not run if we have another NTP daemon installed or
+    FreedomBox runs inside a container where the host manages the time.
+
+    """
+    output = subprocess.check_output([
+        'systemctl', 'show', '--property=ConditionResult', '--value',
+        'systemd-timesyncd'
+    ])
+    return 'yes' in output.decode()