def _all_tag(self):
        """Return the all tag of the Glances/Docker configuration file.

        # By default, Glances only display running containers
        # Set the following key to True to display all containers
        all=True
        """
        all_tag = self.get_conf_value('all')
        if len(all_tag) == 0:
            return False
        else:
            return all_tag[0].lower() == 'true'