code: def main():
      """Main function if tracker is executed in standalone mode."""
      parser = argparse.ArgumentParser(
          description="Rabit Tracker start."
      )
      parser.add_argument(
          "--num-workers",
          required=True,
          type=int,
          help="Number of worker proccess to be launched.",
      )
      parser.add_argument(
          "--num-servers",
          default=0,
          type=int,
          help="Number of server process to be launched. Only used in PS jobs.",
      )
      parser.add_argument(
          "--host-ip",
          default=None,
          type=str,
          help=(
              "Host IP addressed, this is only needed "
              + "if the host IP cannot be automatically guessed."
          ),
      )
      parser.add_argument(
          "--log-level",
          default="INFO",
          type=str,
          choices=["INFO", "DEBUG"],
          help="Logging level of the logger.",
      )
      args = parser.parse_args()
      sys.stdout.write(
          "###PYTHONWARN### args for tracker: " + str(args)
      )
  
      # Open a file and prepare to set the hostname
      with open("/etc/hostname", "r") as f:
          hostname = f.readline().strip()
          socket.sethostname(hostname)
      fmt = "%(asctime)s %(levelname)s %(message)s"
      if args.log_level == "INFO":
          level = logging.INFO
      elif args.log_level == "DEBUG":
          level = logging.DEBUG
      else:
          raise RuntimeError(
              "Unknown logging level %s" % args.log_level
          )
  
      logging.basicConfig(format=fmt, level=level)
  
      if args.num_servers == 0:
          start_rabit_tracker(args)
      else:
          raise RuntimeError(
              "Do not yet support start ps tracker in standalone mode."
          )
  
imports: from __future__ import absolute_import
  import os
  import sys
  import socket
  import struct
  import subprocess
  import argparse
  import time
  import logging
  from threading import Thread
label_desc: Use image node_id 6 for calling a global function with example usage: main() without return types