@makemrproper said in Disk space should never bring a whole server down:
This is still a huge problem.
I understand the desire for an approach that stops the problem happening in the first place. In the interim, I really recommend an alert system like ntfy. Use their hosted service or host it yourself ( have self packaged for Cloudron - more recent version is at https://forum.cloudron.io/post/54552).
Set a cron job for as often as you want, running a script for df -h, set alert levels in the script sending notifications to dashboard or iOS/Android device.
As self-hosters we want to rely on things working, but we can't escape our responsibility to keep an eye on things. ntfy handles this in one of the simplest ways.