def _start_ubridge_capture(self, adapter_number, output_file):
        """
        Start a packet capture in uBridge.

        :param adapter_number: adapter number
        :param output_file: PCAP destination file for the capture
        """

        vnet = "ethernet{}.vnet".format(adapter_number)
        if vnet not in self._vmx_pairs:
            raise VMwareError("vnet {} not in VMX file".format(vnet))
        if not self._ubridge_hypervisor:
            raise VMwareError("Cannot start the packet capture: uBridge is not running")
        yield from self._ubridge_send('bridge start_capture {name} "{output_file}"'.format(name=vnet,
                                                                                           output_file=output_file))