When setting up a DNS server, the Ubuntu documentation says to change
RESOLVCONF=yes in /etc/default/bind9
But it doesn't explain what that actually does. And, I only found it on the "troubleshooting" page; not as part of the configuration steps. Strange.
Some additional reading in a variety of sources leads me to believe that it tells systemd-resolved to consider the local DNS server (presumably first?) in addition to the other nameservers configured in /etc/netplan/ files. But I don't really see that spelled out in so many words ... anywhere.
Also, I can find no way to tell that anything elsewhere has changed. For example, the output of
networkctl status and
systemd-resolve --status both appear to be unchanged after making the change in /etc/default/bind9 and restarting bind9.
So, my questions are:
1) What exactly does setting
RESOLVCONF=yes do? That is, what behavior(s) in which systems does it change?
2) Where can I see the result? That is, what command(s) can I run before and after to see that it has taken effect, either to verify that it is working, or to understand better what it is doing?
3) Where can I find documentation for the answers to #1 and #2.