resolvconf not found (Debian)

On some Linux distributions, including Debian 12 and 13, the Defguard client may fail to establish a VPN tunnel to a location with DNS servers configured. This happens when systemd-resolved is not running and the resolvconf command is not installed, so the client has no way to configure DNS.

Install a package that provides resolvconf:

sudo apt install openresolv

Retry the connection after installation.

With resolvconf and no local resolver such as dnsmasq, the client cannot do split DNS: the VPN's DNS server answers nearly all queries. For split DNS, use systemd-resolved instead:

sudo apt install systemd-resolved
sudo systemctl enable --now systemd-resolved

This changes name resolution for the whole machine: /etc/resolv.conf is replaced with a link to the systemd-resolved local stub resolver. Check that your existing DNS setup works with it before switching. See Failed to configure DNS (Linux).