I would like my newer GNU/Linux system (Ubuntu 18.04 LTS) to use a single, manually-configured, DNS server for all DNS queries. In the past, I could simply do
echo "nameserver 22.214.171.124" | sudo tee /etc/resolv.conf to clobber the
/etc/resolv.conf file and persistently set the DNS server's IP address for my entire system.
On this (and many newer GNU/Linux distributions),
/etc/resolv.conf is managed by the
resolvconf(8) utilties. On Ubuntu 18.04, this file contains a line like this:
As can see by
sudo ss --listening --numeric --processes, the local system's
systemd-resolved DNS stub resolver is bound to this IP address and is listening on port
53 for incoming DNS requests. Therefore, the above
nameserver line in the
/etc/resolv.conf file is directing all applications that do not use
systemd-resolved's D-Bus or glibc API to the
systemd-resolved service via "normal" DNS requests.
That's all fine and well, but all this means that I can no longer simply write persistent changes to the
/etc/resolv.conf file in order to effect a nameserver change.
After reading numerous manual pages and blog posts, I learned that I could set "global" DNS nameserver IP address(es) by editing, for example, the
/etc/systemd/resolve.conf file such that this file contained a line as follows:
After making this change and invoking
sudo systemctl restart systemd-resolved, running
systemd-resolve --status did show the new nameservers (
126.96.36.199) in the "Global" section. However, a Wireshark packet capture confirmed that my system was still sending DNS queries to the "per-link" DNS server presumably configured via DHCP (say,
Further experimentation lead me to add the following line to my
This seems to have successfully instructed
systemd-resolved to always use the global nameservers (set in the
DNS= option) and to never query any DHCP-supplied nameservers, even though those nameservers still show up when I inspect the output of
Finally my questions: Aside from the obvious impact this will have on, say, ignoring VPN-supplied DNS information, what other potential impact will this have on my system? And, more importantly, is there a recommended way to completely override dynamically-configured nameserver settings, such as those provided by DHCP, on a system using
systemd-resolved such as Ubuntu 18.04 that is more complete than simply editing each NetworkManager-managed connection via the GUI? In particular, I do not want to have to edit the DNS settings for each individual Wi-Fi network that I join; I want all connections to automatically always use statically-configured nameservers for DNS resolution. What is the "best" way to do that, and why?