Enable possibility to enforce PollingObserver by setting the environment variable WATCHMEDO_FORCE_POLLING

README.rst

@@ -62,6 +62,12 @@ response to events:
         --command='echo "${watch_src_path}"' \
         .
 
+You can enforce usage of the PollingObserver by setting the environment
+variable WATCHDOG_FORCE_POLLING to an non empty value. This is for example usable
+if you are in an environment where the default observer will not work. For example
+when you are monitoring files on a shared folder inside a virtual machine where
+the host file change events doesn't propagate to the guest.
+
 Please see the help information for these commands by typing:
 
 .. code-block:: bash

docs/source/installation.rst

@@ -163,4 +163,5 @@ Windows Vista and later
 OS Independent Polling
     |project_name| also includes a fallback-implementation that polls
     watched directories for changes by periodically comparing snapshots
-    of the directory tree.
+    of the directory tree. You can enforce this behavior by setting the
+    environment variable WATCHDOG_FORCE_POLLING to a non empty value.

src/watchdog/observers/__init__.py

@@ -55,10 +55,14 @@
 """
 
 import warnings
+import os
 from watchdog.utils import platform
 from watchdog.utils import UnsupportedLibc
 
-if platform.is_linux():
+if os.environ.get('WATCHDOG_FORCE_POLLING', False):
+    from .polling import PollingObserver as Observer
+
+elif platform.is_linux():
     try:
         from .inotify import InotifyObserver as Observer
     except UnsupportedLibc: