I needed to install Ubuntu 18.04 recently and I ran into some problems with OpenVPN 2.4.4 not working (it had worked fine with OpenVPN 2.4.0 from Debian stretch/stable). The errors pointed to
ns-cert-type being the problem, which is indeed a deprecated option. But that led me to find suggestions to instead use
remote-cert-tls server that did not help me get things working.
Rather, the problem ended up being with these options that I'm sometimes required to add to get openvpn working:
up /etc/openvpn/update-resolv-conf down /etc/openvpn/update-resolv-conf
Following the advice from this answer in the Ubuntu forums, I had to make just a few tweaks to get things working.
First, install openvpn-systemd-resolved:
sudo apt install openvpn-systemd-resolved
Second, add these four lines (yes, with
script-security 2) at the end of client.ovpn:
script-security 2 up /etc/openvpn/update-systemd-resolved down /etc/openvpn/update-systemd-resolved down-pre
And now OpenVPN works again:
sudo openvpn --config /path/to/client.ovpn --auth-user-pass /path/to/my.auth