$ sudo modprobe -r rbd
$ sudo modprobe -r libceph
$ lsmod | grep libceph
[1]
$ rbd create --size 1 img
$ DEV=$(sudo rbd map img)
$ sudo grep -q ',key=' /sys/bus/rbd/devices/${DEV#/dev/rbd}/config_info
$ sudo rbd unmap $DEV
$ rbd rm --no-progress img