RBD-NBD(8) Ceph RBD-NBD(8)

# [NAME](#NAME)

rbd-nbd - map rbd images to nbd device

# [SYNOPSIS](#SYNOPSIS)

```
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
```

# [DESCRIPTION](#DESCRIPTION)

**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.

# [OPTIONS](#OPTIONS)

[**-c ceph.conf**](#c)

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

[**--read-only**](#read)

Map read-only.

[**--nbds\_max \*limit\***](#nbds_max)

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

[**--max\_part \*limit\***](#max_part)

Override for module param max\_part.

[**--exclusive**](#exclusive)

Forbid writes by other clients.

[**--notrim**](#notrim)

Turn off trim/discard.

[**--encryption-format**](#encryption)

Image encryption format. Possible values: *luks*, *luks1*, *luks2*

[**--encryption-passphrase-file**](#encryption~2)

Path of file containing a passphrase for unlocking image encryption.

[**--io-timeout \*seconds\***](#io)

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\***](#reattach)

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\***](#snap)

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

# [IMAGE AND SNAP SPECS](#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.

# [AVAILABILITY](#AVAILABILITY)

**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](#SEE_ALSO)

rbd <>(8)

# [Copyright](#Copyright)

2010-2014, Inktank Storage, Inc. and contributors. Licensed under Creative Commons Attribution Share Alike 3.0 (CC-BY-SA-3.0)

September 18, 2026 dev

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Document: rbd-nbd(8) from ceph-fips-18 18.2.8-r9 (Chainguard OS)
Source: https://github.com/ceph/ceph.git