How do I set up the project quota needed for limiting container storage size for the dir backend on Ubuntu 18.04?

[michacassola]

Done.

Enable Project Quota for the DIR storage backend on a live root EXT4 filesystem without live-cd

Thanks to @stgraber telling me that running tune2fs -O project -Q prjquota /dev/sdaX is absolutely essential to enable Project Quota on a device, I searched for a solution that does not require switching off or using a live-cd as this requires too much time and does not always work well in my experience with my VPS provider. And I also hoped that I can turn the steps into a script, which did not work out so far, but is still a possibility. Thanks to a StackExchange question I was able to put …

Thank you guys @tomp @stgraber for all the guidance!