code: def start(self) -> None:
      self._shutdown_event.clear()
      if self._process is not None:
          return None
      logger.info("Starting system monitor")
      self._process = threading.Thread(
          target=self._start, daemon=True, name="SystemMonitor"
      )
      self._process.start()
  
imports: import datetime
  import logging
  import queue
  import threading
  from collections import defaultdict, deque
  from typing import TYPE_CHECKING, Deque, Dict, List, Optional, Tuple
  from .assets.asset_registry import asset_registry
  from .assets.interfaces import Asset, Interface
  from .assets.open_metrics import OpenMetrics
  from .system_info import SystemInfo
label_desc: Use image node_id 7 for calling the SystemMonitor obj's underlying member method code with example usage: obj.start() and returns: None