When deleting a user if you see an error message like this:
Error response from daemon: Cannot destroy container stefan: Driver devicemapper failed to remove root filesystem 656cfd09aee399c8ae8c8d3e735fe48d70be6672773616e15579c8de18e2a3b3: Device is Busy
To fix it, run command umount /var/lib/docker/devicemapper/mnt/ followed by the device id from the error message.
Example:
$ umount /var/lib/docker/devicemapper/mnt/656cfd09aee399c8ae8c8d3e735fe48d70be6672773616e15579c8de18e2a3b3
❗️ NOTE: devicemapper is deprecated and will be replaced with overlay2 as the default storage engine: https://community.openpanel.co/d/8-switching-docker-storage-engine-from-devicemapper-to-overlay2-storage