Failed to configure DNS (Linux)

This error commonly appears on Ubuntu 22. The Defguard client uses resolvconf internally to configure DNS servers on the system. The only tested and supported backend is systemd-resolved.

Before proceeding, verify that systemd-resolved is running:

systemctl status systemd-resolved

Ubuntu 22

On Ubuntu 23 and later, resolvconf is a symbolic link to resolvectl by default. On Ubuntu 22 this link does not exist. The straightforward fix is to create it manually:

sudo ln -s /usr/bin/resolvectl /usr/sbin/resolvconf

If that fails, you can also try installing a package that provides the resolvconf command, such as openresolv. Note that using openresolv alongside systemd-resolved has not been tested and may cause conflicts — proceed with caution.

DNS resolution check

If DNS servers are configured in the location but users cannot resolve internal hostnames, check the following:

1. Routing — confirm requests to the network segments where your DNS servers reside are routed through the WireGuard interface:

   ip route

2. WireGuard allowed IPs — confirm the DNS server network segments appear in the allowed ips list for the peer:

   sudo wg

3. Manual resolution test — try resolving a name directly through one of your internal DNS servers:

   dig @DNS_SERVER_IP my.internal.service.com