For the longest time /etc/resolv.conf has been a very simple little file telling Linux where to go for DNS resolution. These days it’s quite the popular file. System daemons old and new are lining up to have their way with what should be a very simple little config. Leading to memes like this one:
While some will symlink to their own file, others want to set up a local caching resolver and point to that. The problem with most of these is that roaming between networks will break your config should you have a mobile device. And local resolution won’t work if you are using a local resolver like systemd-resolved wants to do. It’s not exactly difficult to get into a situation where more than one is installed in which case they fight to wrest control of the single config file. So how do we unfuck this mess? Let’s look at Ubuntu, which now ships with systemd-resolved.
By default we can see that systemd-resolved has a symlink in place. It’s set up a local resolver that won’t respect your upstream DNS that should be assigned by your DHCP server.
So…let’s kill that.
Now that Lennart Poettering has been sufficiently triggered we can tell NetworkManager to do its job.
The old symlink is still in place, so that needs to be removed. A restart of the NetworkManager service writes out a new resolv.conf with the actually assigned DHCP DNS nameservers.
It only took five minutes to fix something that shouldn’t have been broken in the first place. 🤦