If OpenVPN client breaks DNS configuration

Sometimes, Linux OpenVPN client changes DNS configuration and then <VPN server domain> becomes unreachable so you get error messages like:

RESOLVE: Cannot resolve host address: <VPN server domain here> (Name or service not known)

On initial connection you see this output in the console:

dhcp-option DNS <IP here>
dhcp-option DOMAIN <VPN server domain here>
/sbin/ip route add <IP here>/32 via <IP here>

systemd-resolve --status command shows this:

Global

         DNS Servers: <IP from above here>

          DNS Domain: <domain here>

...

cat /etc/resolv.conf command shows new DNS configuration by OpenVPN:

...

search <domain here>

To resolve this issue, just remove this new line from /etc/resolv.conf with an editor, e.g.

sudo nano /etc/resolv.conf

or delete the line with sed:

sudo sed -i.bak '/<domain>/d' /etc/resolv.conf

or restore from a backup but be aware that the file could really be a link, e.g. 

resolv.conf -> /run/resolvconf/resolv.conf

UPDATE: resolv.conf is most likely dynamically generated instead of a static file.

E.g. in Ubuntu check your NetworkManager configuration:

sudo NetworkManager --print-config

if there's

dns=systemd-resolved

then edit settings in

/run/resolvconf/interface/systemd-resolved

and update

sudo resolvconf -u

In my case there was also

/run/resolvconf/interface/tun0.openvpn

file (created by OpenVPN) which can be safely deleted to avoid interference:

sudo rm /run/resolvconf/interface/tun0.openvpn

The DNS settings should be back to normal now, if not, you may need to run

service networking restart

I have this function defined in .bash_aliases which fixes DNS configuration before connecting via OpenVPN:

vpn_fixed_dns() {
    echo "Fixing resolv.conf"
    echo "nameserver 127.0.0.53" | sudo tee /run/resolvconf/interface/systemd-resolved >/dev/null
    sudo rm /run/resolvconf/interface/tun0.openvpn
    echo "Running sudo resolvconf -u"
    sudo resolvconf -u
    cat /etc/resolv.conf
    echo "Running sudo openvpn"
    sudo openvpn --script-security 2 --config /etc/openvpn/config/config.ovpn

}