Ceph » rbd

#rbd-nbd --help
Usage: rbd-nbd [options] map <image-or-snap-spec> Map an image to nbd device
unmap <device path> Unmap nbd device
list-mapped List mapped nbd devices
Options:
--device <device path> Specify nbd device path
--read-only Map read-only
--nbds_max <limit> Override for module param nbds_max
--max_part <limit> Override for module param max_part
--exclusive Forbid writes by other clients

--conf/-c FILE read configuration from the given configuration file
--id/-i ID set ID portion of my name
--name/-n TYPE.ID set name
--cluster NAME set cluster name (default: ceph)
--setuser USER set uid to user or uid (and gid to user's gid)
--setgroup GROUP set gid to group or gid
--version show version and quit

-d run in foreground, log to stderr.
-f run in foreground, log to usual location.
--debug_ms N set message debug level (e.g. 1)

We could find --conf/-c print out in help message. But when use it:
#rbd-nbd map image -c /etc/ceph/ceph.conf
rbd-nbd: unknown args: -c