code: def _check_duplicate_linked_clone(self):
          
          trial = 0
  
          while True:
              found = False
              for node in self.manager.nodes:
                  if node != self and node.vmname == self.vmname:
                      found = True
                      if node.project != self.project:
                          if trial >= 30:
                              raise VirtualBoxError("Sorry a node without the linked clone setting enabled can only be used once on your server.\n{} is already used by {} in project {}".format(self.vmname, node.name, self.project.name))
                      else:
                          if trial >= 5:
                              raise VirtualBoxError("Sorry a node without the linked clone setting enabled can only be used once on your server.\n{} is already used by {} in this project".format(self.vmname, node.name))
              if not found:
                  return
              trial += 1
              yield from asyncio.sleep(1)
docs: Without linked clone two VM using the same image can't run
          at the same time.
  
          To avoid issue like false detection when a project close
          and another open we try multiple times.