Update the package lists.
sudo apt-get update
Install resolvconf. 
sudo apt-get install resolvconf
Users preferring not to install resolvconf should read the footnotes. 
- /etc/openvpn/update-resolv-conf uses resolvconf. resolvconf needs to be installed for the lines beginning with script-security, up, and down to function properly.
In the /etc/openvpn/openvpn.conf file, change the following text.
script-security 2 up "/etc/openvpn/update-resolv-conf script_type=up dev=tun0" down "/etc/openvpn/update-resolv-conf script_type=down dev=tun0"
To the following. Remove or comment out the lines beginning with "up" and "down", and change the 2 to a 1.
Open /etc/resolv.conf in an editor with root rights.
## Riseup.net OpenVPN DNS server nameserver 172.27.100.1
If Riseup is not being used, replace 172.27.100.1 with the virtual LAN IP address of the VPN provider's DNS server. If unsure, the VPN provider might provide it. Users can also try to infer it by running sudo route after successfully connecting to the VPN. The first destination default gateway should also function as a DNS server.
Save and exit.
Users who want to prevent /etc/resolv.conf being overwritten by other packages like DHCP or resolvconf should run.
sudo chattr +i /etc/resolv.conf
In order to revert this change, use -i.
Ignore the /etc/resolv.conf instructions below.