<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def start(self):
 """ Starts this router. At least the IOS image must be set before it can start. """


        status = yield from self.get_status()
        if status == "suspended":
            yield from self.resume()
        elif status == "inactive":

            if not os.path.isfile(self._image) or not os.path.exists(self._image):
                if os.path.islink(self._image):
                    raise DynamipsError('IOS image "{}" linked to "{}" is not accessible'.format(self._image, os.path.realpath(self._image)))
                else:
                    raise DynamipsError('IOS image "{}" is not accessible'.format(self._image))

            try:
                with open(self._image, "rb") as f:
                    # read the first 7 bytes of the file.
                    elf_header_start = f.read(7)
            except OSError as e:
                raise DynamipsError('Cannot read ELF header for IOS image "{}": {}'.format(self._image, e))

            # IOS images must start with the ELF magic number, be 32-bit, big endian and have an ELF version of 1
            if elf_header_start != b'\x7fELF\x01\x02\x01':
                raise DynamipsError('"{}" is not a valid IOS image'.format(self._image))

            # check if there is enough RAM to run
            if not self._ghost_flag:
                self.check_available_ram(self.ram)

            # config paths are relative to the working directory configured on Dynamips hypervisor
            startup_config_path = os.path.join("configs", "i{}_startup-config.cfg".format(self._dynamips_id))
            private_config_path = os.path.join("configs", "i{}_private-config.cfg".format(self._dynamips_id))

            if not os.path.exists(os.path.join(self._working_directory, private_config_path)) or \
               not os.path.getsize(os.path.join(self._working_directory, private_config_path)):
                # an empty private-config can prevent a router to boot.
                private_config_path = ''

            yield from self._hypervisor.send('vm set_config "{name}" "{startup}" "{private}"'.format(
                name=self._name,
                startup=startup_config_path,
                private=private_config_path))
            yield from self._hypervisor.send('vm start "{name}"'.format(name=self._name))
            self.status = "started"
            log.info('router "{name}" [{id}] has been started'.format(name=self._name, id=self._id))

            self._memory_watcher = FileWatcher(self._memory_files(), self._memory_changed, strategy='hash', delay=30)
            monitor_process(self._hypervisor.process, self._termination_callback)