---
name: "nbdtab"
section: "5"
platform: "linux"
package: "nbd"
version: "3.27.1-4"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/nbdtab"
---

# nbdtab(5)

configuration file for nbd-client

## NAME

/etc/nbdtab - configuration file for nbd-client

## SYNOPSIS

**/etc/nbdtab**

## DESCRIPTION

This file allows to configure predefined connections for nbd-client. It may contain multiple definitions, one per line, each of which contains four space-separated fields.

To connect a device specified in the nbdtab file, run [**nbd-client**(8)](/nbd-client/8.md) with the short name of that device as the sole argument. It will then look up the required information in *nbdtab*, and make the connection.

Fields are separated from one another by any number of space or tab characters; records are separated from one another by newline characters. The file may also contain any number of comments, which start with a '#' character and continue until the end of the line or the end of the file, whichever is first.

### FIELDS

The file contains the following fields:

- 1\.

  The short name of the device file. That is, it should contain the name of the device without the leading */dev/* part; e.g., it could say *nbd0*.

- 2\.

  The hostname (in case of a TCP socket) or filename (in case of a unix domain socket) on which the server is listening.

- 3\.

  The name of the export as exported by **nbd-server**.

- 4\.

  Any extra options. This field is optional (no pun intended), and need not appear in a file if no options are necessary. The options recognized by [**nbd-client**(8)](/nbd-client/8.md) are specified below, in the section "Options". Any unknown options in this field will produce a warning by **nbd-client**, unless they are prepended by an underscore ('\_') character; the underscore is specifically reserved for local use, or for distribution customization.

### OPTIONS

Every command-line **nbd-client** option which allows to configure specific options for a particular device node has a corresponding option in the *nbdtab* file, and vice versa; where this isn't the case, that is a bug.

Individual options in this field should be separated from one another by the comma character.

- **bs=***block size*

  The block size for this export. If this option is not used, the kernel's default will be used instead.

  Corresponds to the **-b** option on the command line.

- **cacertfile=***certificate file*

  The CA certificate file for TLS. Corresponds to the **-A** option on the command line.

- **certfile=***certificate file*

  The certificate file for TLS. Corresponds to the **-F** option on the command line.

- **conns=***number*

  The number of connections to use for this device. Corresponds to the **-C** option on the command line; see [nbd-client(8)](/nbd-client/8.md) for more details on that option.

- **keyfile=***key file*

  The private key file for TLS. Corresponds to the **-K** option on the command line.

- **no\_optgo**

  Disable the use of NBD\_OPT\_GO in the conversation. Corresponds to the **-g** option on the command line.

- **persist**

  Persist the connection, using the semantics of the **-p** command-line option.

- **port=***port number*

  The port on which to communicate with the **nbd-server**. Defaults to the IANA-assigned port for NBD, 10809.

- **priority=***GnuTLS priority string* **The GnuTLS priority string to use. Corresponds to the -y option on the command line.**

  - **swap**

  Optimize for swap; **-s**.

- **timeout=***timeout*

  The timeout. If this option is not specified, no timeout is configured.

  Corresponds to the **-t** option on the command line.

- **tlshostname=***TLS hostname*

  The hostname for TLS purposes; **-H**

- **unix**

  Use a Unix Domain socket to connect to the server; **-u**.

## SEE ALSO

nbd-server (1), nbd-client (8), nbd-trdump (8)

## AUTHOR

The NBD kernel module and the NBD tools were originally written by Pavel Machek (pavel@ucw.cz)

The Linux kernel module is now maintained by Paul Clements (Paul.Clements@steeleye.com), while the userland tools are maintained by Wouter Verhelst (\<wouter@debian.org\>)

On The Hurd there is a regular translator available to perform the client side of the protocol, and the use of **nbd-client** is not required. Please see the relevant documentation for more information.

This manual page was written by Wouter Verhelst (\<wouter@debian.org\>). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, version 2, as published by the Free Software Foundation.

## EXAMPLES

A simple *nbdtab* file could look like this:

```
# swap space, called "swapexport" on the server
# optimize for swap, and try to reconnect upon disconnect.
nbd0 nbdserver.example.com swapexport swap,persist
# other export, called "data" on the server. No options for this one.
nbd1 nbdserver.example.com data
```