This post describes different software components involved in host name resolutions and DNS configuration on GNU/Linux systems. It consists of a diagram and some accompanying explanations. The goal is to give some pointers and references to understand how to troubleshoot host name/DNS resolution problems and configuration problems on GNU/Linux systems.
Some guidance about configuring/fixing domain name resolution with a corporate Virtual Private Network (VPN), especially OpenVPN, with systemd-based Linux systems. This configuration uses the internal/private corporate resolvers for resolving internal/private domain names while using the ISP resolver for general domain names. This might help if your VPN is struggling these days because of the COVID-19 threat .
How I found remote code execution vulnerabilities via Cross Site Request Forgery (CSRF) on the administration interfaces of InternetCube applications and of the YunoHost administration interface which could have been used to execute arbitrary code as root. These vulnerabilities were fixed in YunoHost 3.3, OpenVPN Client app 1.3.0. and YunoHost 3.4.