code: def pid_lock(path):
      
  
      if os.path.exists(path):
          pid = None
          try:
              with open(path) as f:
                  try:
                      pid = int(f.read())
                      os.kill(pid, 0)  # kill returns an error if the process is not running
                  except (OSError, SystemError, ValueError):
                      pid = None
          except OSError as e:
              log.critical("Can't open pid file %s: %s", pid, str(e))
              sys.exit(1)
  
          if pid:
              log.critical("GNS3 is already running pid: %d", pid)
              sys.exit(1)
  
      try:
          with open(path, 'w+') as f:
              f.write(str(os.getpid()))
      except OSError as e:
          log.critical("Can't write pid file %s: %s", path, str(e))
          sys.exit(1)
docs: Write the file in a file on the system.
      Check if the process is not already running.