If you landed there, you are surely dealing with real containers (take that Docker), and within real containers, we keep the system up to date, isn’t it ?
When you have only few containers, doing system updates is quick and easy.
When you have many containers, it’s getting boring.
Below is a (maintained) script to perform automatic updates, within your running containers, on top of Proxmox 5.
No conclusion, but a big thank to the author of this blog post, for its BASH-syntax escaping alchemy, allowing us to execute operation from outside the container.