Example URIs supported

"nbd://example.com"

Connect over TCP, unencrypted, to "example.com" port 10809.

"nbds://example.com"

Connect over TCP with TLS, to "example.com" port 10809. If the server does not support TLS then this will fail.

"nbd+unix:///foo?socket=/tmp/nbd.sock"

Connect over the Unix domain socket /tmp/nbd.sock to an NBD server running locally. The export name is set to "foo" (note without any leading "/" character).

"nbds+unix://alice@/?socket=/tmp/nbd.sock&tls-certificates=certs"

Connect over a Unix domain socket, enabling TLS and setting the path to a directory containing certificates and keys.

"nbd+vsock:///"

In this scenario libnbd is running in a virtual machine. Connect over "AF_VSOCK" to an NBD server running on the hypervisor.

Supported URI formats

The following schemes are supported in the current version of libnbd:

"nbd:"

Connect over TCP without using TLS.

"nbds:"

Connect over TCP. TLS is required and the connection will fail if the server does not support TLS.

"nbd+unix:"

"nbds+unix:"

Connect over a Unix domain socket, without or with TLS respectively. The "socket" parameter is required.

"nbd+vsock:"

"nbds+vsock:"

Connect over the "AF_VSOCK" transport, without or with TLS respectively.

The authority part of the URI ("[username@][servername][:port]") is parsed depending on the transport. For TCP it specifies the server to connect to and optional port number. For "+unix" it should not be present. For "+vsock" the server name is the numeric CID (eg. 2 to connect to the host), and the optional port number may be present. If the "username" is present it is used for TLS authentication.

For all transports, an export name may be present, parsed in accordance with the NBD URI specification.

Finally the query part of the URI can contain:

socket=SOCKET

Specifies the Unix domain socket to connect on. Must be present for the "+unix" transport and must not be present for the other transports.

tls-certificates=DIR

Set the certificates directory. See nbd_set_tls_certificates(3). Note this is not allowed by default - see next section.

tls-psk-file=PSKFILE

Set the PSK file. See nbd_set_tls_psk_file(3). Note this is not allowed by default - see next section.

Disable URI features

For security reasons you might want to disable certain URI features. Pre-filtering URIs is error-prone and should not be attempted. Instead use the libnbd APIs below to control what can appear in URIs. Note you must call these functions on the same handle before calling nbd_connect_uri(3) or nbd_aio_connect_uri(3).

TCP, Unix domain socket or "AF_VSOCK" transports

Default: all allowed

To select which transports are allowed call nbd_set_uri_allow_transports(3).

TLS

Default: both non-TLS and TLS connections allowed

To force TLS off or on in URIs call nbd_set_uri_allow_tls(3).

Connect to Unix domain socket in the local filesystem

Default: allowed

To prevent this you must disable the "+unix" transport using nbd_set_uri_allow_transports(3).

Read from local files

Default: denied

To allow URIs to contain references to local files (eg. for parameters like "tls-psk-file") call nbd_set_uri_allow_local_file(3).

Overriding the export name

It is possible to override the export name portion of a URI by using nbd_set_opt_mode(3) to enable option mode, then using nbd_set_export_name(3) and nbd_opt_go(3) as part of subsequent negotiation.

Optional features

This call will fail if libnbd was not compiled with libxml2; you can test whether this is the case with nbd_supports_uri(3).

Support for URIs that require TLS will fail if libnbd was not compiled with gnutls; you can test whether this is the case with nbd_supports_tls(3).

Constructing a URI from an existing connection

See nbd_get_uri(3).