Fixing Ubuntu Linux "Temporary failure in name resolution"

I have a virtual machine running Pi-Hole on Ubuntu Linux 18.04. I decided to upgrade, in place, to 20.04. After the upgrade, I realized that the server itself had DNS issues. It couldn't connect to get updates, and when I logged in via SSH, it couldn't resolve when running a ping.

Solution

I noticed that my default DNS server in resolv.conf was 127.0.0.53. This is always overwritten, and I didn't fully understand why until reading this post. Following the steps, including editing, resolved.conf gets you the solution. The screenshots below are for verification purposes.

Checking system status shows Linux resolving to Google's Public DNS server (8.8.8.8)

Another thing that worked for me and wasn't listed in the forum posting above was the need to redo a symbolic link.

Last two lines of screen capture show how to remove old symbolic link and create a new one.