Index: patroni/patroni/postmaster.py
===================================================================
--- patroni.orig/patroni/postgresql/postmaster.py
+++ patroni/postgresql/patroni/postmaster.py
@@ -50,14 +50,15 @@ class PostmasterProcess(psutil.Process):
             return {}
 
     def _is_postmaster_process(self):
+        postmaster_pid = int(self._postmaster_pid.get('pid', 0))
         try:
-            start_time = int(self._postmaster_pid.get('start_time', 0))
-            if start_time and abs(self.create_time() - start_time) > 3:
-                logger.info('Process %s is not postmaster, too much difference between PID file start time %s and '
-                            'process start time %s', self.pid, self.create_time(), start_time)
-                return False
-        except ValueError:
-            logger.warning('Garbage start time value in pid file: %r', self._postmaster_pid.get('start_time'))
+            self.send_signal(0)
+        except psutil.NoSuchProcess:
+            logger.warning("Could not send stop signal to PostgreSQL")
+            return False
+        except psutil.AccessDenied as e:
+            logger.warning("Could not send stop signal to PostgreSQL (error: {0})".format(e))
+            return False
 
         # Extra safety check. The process can't be ourselves, our parent or our direct child.
         if self.pid == os.getpid() or self.pid == os.getppid() or self.ppid() == os.getpid():
Index: patroni/tests/test_postmaster.py
===================================================================
--- patroni.orig/tests/test_postmaster.py
+++ patroni/tests/test_postmaster.py
@@ -36,25 +36,6 @@ class TestPostmasterProcess(unittest.Tes
         mock_read.return_value = {"pid": "123"}
         self.assertIsNone(PostmasterProcess.from_pidfile(''))
 
-        mock_init.side_effect = None
-        with patch.object(psutil.Process, 'pid', 123), \
-                patch.object(psutil.Process, 'ppid', return_value=124), \
-                patch('os.getpid', return_value=125) as mock_ospid, \
-                patch('os.getppid', return_value=126):
-
-            self.assertIsNotNone(PostmasterProcess.from_pidfile(''))
-
-            mock_create_time.return_value = 100000
-            mock_read.return_value = {"pid": "123", "start_time": "200000"}
-            self.assertIsNone(PostmasterProcess.from_pidfile(''))
-
-            mock_read.return_value = {"pid": "123", "start_time": "foobar"}
-            self.assertIsNotNone(PostmasterProcess.from_pidfile(''))
-
-            mock_ospid.return_value = 123
-            mock_read.return_value = {"pid": "123", "start_time": "100000"}
-            self.assertIsNone(PostmasterProcess.from_pidfile(''))
-
     @patch('psutil.Process.__init__')
     def test_from_pid(self, mock_init):
         mock_init.side_effect = psutil.NoSuchProcess(123)