I've just upgraded my laptop from Xubuntu 17.04 to 17.10. After the final reboot, DNS has stopped working. This is obviously a problem! I can ping known IP addresses; just no DNS resolution.
I've not fiddled with any DNS settings; as far as I know, I had the standard DNS configuration previously. Its just a laptop which uses DHCP to get details from my home WiFi router.
Obviously, the ability to diagnose this is limited when the system itself can't resolve any web addresses. I did some googling on my phone, and most of the answers I found seemed to recommend turning dnsmasq off. However, dnsmasq was already off. But
/etc/resolv.conf was showing 127.0.1.1, which seems to imply that it was expecting dnsmasq to be running.
I turned dnsmasq ON, by editing
and then I ran this command
sudo systemctl restart NetworkManager
My DNS resolution is now working.
However, given that the default Ubuntu configuration is not to use dnsmasq, what should I actually have done to diagnose and fix this instead?