If you installed Debian 8.0 or Ubuntu 15.04 with an active IPv6 connection and have upgraded your system, you may end up with both resolvconf and rdnssd fighting each other for control over resolv.conf.

Both services want to control the file, which may lead to intermittent DNS resolution outages as the two services overwrite each other’s changes every few milliseconds.

You can disable both services with the following commands. You can just go ahead and run both commands, as nothing unexpected should happen if disable an already disabled service.

systemctl disable --now resolvconf.service rdnssd.service
rm /etc/resolv.conf

See Opting-out of NetworkManager, as it may step in automatically to handle the resolv.conf file after you remove it.