1. https://learnku.com/articles/21457
  2. https://www.ctolib.com/topics-99089.html
  3. http://www.chengweiyang.cn/2015/11/14/how-to-enlarge-linux-open-files-upper-cell/
  4. cat /proc/PID/limits  查看进程能打开的文件数。
  5. 守护进程修改不了open  files