code: def validate_services(self, commands):
          
          self.log.debug('Checking status of system services...')
  
          # /!\ DEPRECATION WARNING (beisner):
          # New and existing tests should be rewritten to use
          # validate_services_by_name() as it is aware of init systems.
          self.log.warn('DEPRECATION WARNING:  use '
                        'validate_services_by_name instead of validate_services '
                        'due to init system differences.')
  
          for k, v in six.iteritems(commands):
              for cmd in v:
                  output, code = k.run(cmd)
                  self.log.debug('{} `{}` returned '
                                 '{}'.format(k.info['unit_name'],
                                             cmd, code))
                  if code != 0:
                      return "command `{}` returned {}".format(cmd, str(code))
          return None
docs: Validate that lists of commands succeed on service units.  Can be
             used to verify system services are running on the corresponding
             service units.
  
          :param commands: dict with sentry keys and arbitrary command list vals
          :returns: None if successful, Failure string message otherwise