@zach Thank you for your remark.
Unfortunately I have general issues with the VPS at provider Servinga: A reboot of the server fails due to (according boot in VNC-Console) a unified cdrom-driver. Unfortunately there are no cdrom-Options on their Management-Portal as well as there are no easy settings possible to change the boot-order.
I therefore will change the VPS-Provider.
Unfortunately - what a lucky guy I am - new problems over there; wil post a new thread shortly.