code: def server_shutdown(server_state):
      
      set_running( False )
  
      # stop API servers
      rpc_stop(server_state)
      api_stop(server_state)
  
      # stop atlas node
      server_atlas_shutdown(server_state)
  
      # stopping GC
      gc_stop()
  
      # clear PID file
      try:
          if os.path.exists(server_state['pid_file']):
              os.unlink(server_state['pid_file'])
      except:
          pass
  
      return True
docs: Shut down server subsystems.
      Remove PID file.