Update the output filename (preferred_filename) so that we can notify it correctly to the user

volatility3/cli/__init__.py

@@ -789,8 +789,16 @@ class CommandLine:
                 if self._file.closed:
                     return None
 
-                self._file.close()
                 output_filename = self._get_final_filename()
+
+                # Update the filename, which may have changed if a file with
+                # the same name already existed. This needs to be done before
+                # closing the file, otherwise FileHandlerInterface will raise
+                # an exception. Also, the preferred_filename setter only allows
+                #  a specific set of characters, where '/' is not in that list
+                self.preferred_filename = os.path.basename(output_filename)
+
+                self._file.close()
                 os.rename(self._name, output_filename)
 
         if direct:

volatility3/framework/plugins/layerwriter.py

@@ -115,6 +115,10 @@ class LayerWriter(plugins.PluginInterface):
                             progress_callback=self._progress_callback,
                         )
                         file_handle.close()
+
+                        # Update the filename, which may have changed if a file
+                        # with the same name already existed.
+                        output_name = file_handle.preferred_filename
                     except IOError as excp:
                         yield 0, (f"Layer cannot be written to {output_name}: {excp}",)