More helpful error when renewing with standalone

letsencrypt/plugins/standalone.py

@@ -200,7 +200,8 @@ class Authenticator(common.Plugin):
         return self.supported_challenges
 
     def perform(self, achalls):  # pylint: disable=missing-docstring
-        if any(util.already_listening(port) for port in self._necessary_ports):
+        renewer = self.config.verb == "renew"
+        if any(util.already_listening(port, renewer) for port in self._necessary_ports):
             raise errors.MisconfigurationError(
                 "At least one of the (possibly) required ports is "
                 "already taken.")

letsencrypt/plugins/standalone_test.py

@@ -125,7 +125,7 @@ class AuthenticatorTest(unittest.TestCase):
             self.config.standalone_supported_challenges = chall
             self.assertRaises(
                 errors.MisconfigurationError, self.auth.perform, [])
-            mock_util.already_listening.assert_called_once_with(port)
+            mock_util.already_listening.assert_called_once_with(port, False)
             mock_util.already_listening.reset_mock()
 
     @mock.patch("letsencrypt.plugins.standalone.zope.component.getUtility")

letsencrypt/plugins/util.py

@@ -11,7 +11,7 @@ from letsencrypt import interfaces
 logger = logging.getLogger(__name__)
 
 
-def already_listening(port):
+def already_listening(port, renewer=False):
     """Check if a process is already listening on the port.
 
     If so, also tell the user via a display notification.
@@ -49,11 +49,18 @@ def already_listening(port):
             pid = listeners[0]
             name = psutil.Process(pid).name()
             display = zope.component.getUtility(interfaces.IDisplay)
+            extra = ""
+            if renewer:
+                extra = (" For automated renewal, you may want to use a script that stops"
+                         " and starts your webserver. You can find an example at"
+                         " https://letsencrypt.org/howitworks/#writing-your-own-renewal-script"
+                         ". Alternatively you can use the webroot plugin to renew without"
+                         " needing to stop and start your webserver.")
             display.notification(
                 "The program {0} (process ID {1}) is already listening "
                 "on TCP port {2}. This will prevent us from binding to "
                 "that port. Please stop the {0} program temporarily "
-                "and then try again.".format(name, pid, port))
+                "and then try again.{3}".format(name, pid, port, extra))
             return True
     except (psutil.NoSuchProcess, psutil.AccessDenied):
         # Perhaps the result of a race where the process could have