Comment 2 for bug 1638836

If such a comment were to be added then in order not to mislead it would have to take into account the configurability of various components. So you'd have to say something like:

«If the line "nameserver 127.0.0.53" is present then it probably refers to the systemd resolver listening on the loopback address. By default the systemd resolver is also configured to handle name queries via the Name Service Switch whose configuration file is nsswitch.conf. The name servers to which the systemd resolver forwards queries can be discovered by running "systemd-resolve --status".»

What would be far better, though, is to include a text file or manpage explaining how name service currently works in Ubuntu. (Actually we should have done this long ago.) The file could include the previous paragraph but would also talk about resolvconf and NetworkManager and its plugins. The name of this file could then be mentioned in the header that resolvconf writes into resolv.conf. /etc/resolvconf/resolv.conf.d/head would then be:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# For more info see /usr/share/doc/resolvconf/name-service-in-Ubuntu.txt
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN