change dns ubuntu 20.04 code example

Example 1: flush dns ubuntu 18.04

sudo systemd-resolve --flush-caches

Example 2: add dns in ubuntu permanently

sudo apt update
sudo apt install resolvconf

sudo systemctl start resolvconf.service
sudo systemctl enable resolvconf.service
sudo systemctl status resolvconf.service

sudo vim /etc/resolvconf/resolv.conf.d/head
and add the following lines in it:
nameserver 8.8.8.8 
nameserver 8.8.4.4

sudo systemctl start resolvconf.service