rbd-nbd – map rbd images to nbd device


rbd-nbd [-c conf] [–read-only] [–device nbd device] [–snap-id snap-id] [–nbds_max limit] [–max_part limit] [–exclusive] [–notrim] [–encryption-format format] [–encryption-passphrase-file passphrase-file] [–io-timeout seconds] [–reattach-timeout seconds] map image-spec | snap-spec
rbd-nbd unmap nbd device | image-spec | snap-spec
rbd-nbd list-mapped
rbd-nbd attach –device nbd device image-spec | snap-spec
rbd-nbd detach nbd device | image-spec | snap-spec


rbd-nbd is a client for RADOS block device (rbd) images like rbd kernel module. It will map a rbd image to a nbd (Network Block Device) device, allowing access it as regular local block device.


-c ceph.conf

Use ceph.conf configuration file instead of the default /etc/ceph/ceph.conf to determine monitor addresses during startup.


Map read-only.

--nbds_max *limit*

Override the parameter nbds_max of NBD kernel module when modprobe, used to limit the count of nbd device.

--max_part *limit*

Override for module param max_part.


Forbid writes by other clients.


Turn off trim/discard.


Image encryption format. Possible values: luks1, luks2


Path of file containing a passphrase for unlocking image encryption.

--io-timeout *seconds*

Override device timeout. Linux kernel will default to a 30 second request timeout. Allow the user to optionally specify an alternate timeout.

--reattach-timeout *seconds*

Specify timeout for the kernel to wait for a new rbd-nbd process is attached after the old process is detached. The default is 30 second.

--snap-id *snapid*

Specify a snapshot to map/unmap/attach/detach by ID instead of by name.

Image and snap specs

image-spec is [pool-name]/image-name
snap-spec is [pool-name]/image-name@snap-name

The default for pool-name is “rbd”. If an image name contains a slash character (‘/’), pool-name is required.


rbd-nbd is part of Ceph, a massively scalable, open-source, distributed storage system. Please refer to the Ceph documentation at https://docs.ceph.com/ for more information.

See also