How to fix OpenVPN 'failed to find UID for user openvpn'

Problem:

In your OpenVPN server logs you see this error message

failed to find UID for user openvpn

followed by a server restart (Exiting due to fatal error).

Solution

Run this command to add the openvpn user and add that user to the openvpn group:

sudo useradd openvpn -g openvpn