2021
https://opensource.com/article/18/7/sysadmin-guide-networking-commands
    https://bookflow.ru/rukovodstvo-sistemnogo-administratora-po-setevym-instrumentam-linux/
https://www.tecmint.com/command-line-tools-to-monitor-linux-performance/
https://www.tecmint.com/find-out-which-process-listening-on-a-particular-port/