/run/resolvconf/resolv.conf ubuntu 18.04
In Ubuntu 18.04 and later, the usual arrangement is:
ls -al /etc/resolv.conf
/etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf
If yours is not the same, I suggest that you do:
sudo rm -f /etc/resolv.conf
ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
Reboot.