code: def get_ostypes():
          
          LOGGER.debug("OSTypeService.get_ostypes")
          args = {'http_operation': 'GET', 'operation_path': ''}
          response = OSTypeService.requester.call(args)
          ret = None
          if response.rc == 0:
              ret = []
              for os_type in response.response_content['osTypes']:
                  ret.append(OSType.json_2_ostype(os_type))
          elif response.rc != 404:
              err_msg = 'OSTypeService.get_ostypes - Problem while getting OS Types.' \
                        '. Reason: ' + str(response.response_content) + '-' + str(response.error_message) + \
                        " (" + str(response.rc) + ")"
              LOGGER.warning(err_msg)
  
          return ret
docs: :return: all knows OS types