focal (1) nbdkit-nbd-plugin.1.gz

NAME

       nbdkit-nbd-plugin - nbdkit nbd plugin

SYNOPSIS

        nbdkit nbd { socket=SOCKNAME | hostname=HOST [port=PORT] | [uri=]URI }
           [export=NAME] [retry=N] [shared=BOOL] [tls=MODE] [tls-certificates=DIR]
           [tls-verify=BOOL] [tls-username=NAME] [tls-psk=FILE]

DESCRIPTION

       "nbdkit-nbd-plugin" is an NBD forwarding plugin for nbdkit(1).

       It provides an NBD server that forwards all traffic as a client to another existing NBD server.  A
       primary usage of this setup is to alter the set of features available to the ultimate end client, without
       having to change the original server (for example, to convert between oldstyle and newstyle, or to add
       TLS support where the original server lacks it).  Use of this plugin along with nbdkit filters (adding
       --filter to the nbdkit command line) makes it possible to apply any nbdkit filter to any other NBD
       server.

       Remember that when using this plugin as a bridge between an encrypted and a non-encrypted endpoint, it is
       best to preserve encryption over TCP and use plaintext only on a Unix socket.

PARAMETERS

       One of socket, hostname or uri must be provided to designate the server. The server can speak either new
       or old style protocol. "uri=" is a magic config key and may be omitted in most cases.  See "Magic
       parameters" in nbdkit(1).

       The following parameters are available whether or not the plugin was compiled against libnbd:

       socket=SOCKNAME
           Connect to the NBD server located at the Unix socket "SOCKNAME".

       hostname=HOST
           Connect to the NBD server at the given remote "HOST" using a TCP socket.

       port=PORT
           When hostname is supplied, use PORT instead of the default port 10809.

       export=NAME
           If this parameter is given, and the server speaks new style protocol, then connect to the named
           export instead of the default export (the empty string). If "uri" is supplied, the export name should
           be embedded in the URI instead.

       retry=N
           If the initial connection attempt to the server fails, retry up to N times more after a one-second
           delay between tries (default 0).

       shared=BOOL
           If this parameter is false (default), the plugin will open a distinct connection to the server for
           each client making a connection to nbdkit, and the remote server does not have to be started until
           immediately before the first nbdkit client.  If this parameter is set to true, the plugin will open a
           single connection to the server when nbdkit is first started (the "delay" parameter may be necessary
           to coordinate timing of the remote server startup), and all clients to nbdkit will share that single
           connection.

       The following parameters are only available if the plugin was compiled against libnbd:

       uri=URI
           When uri is supplied, decode URI to determine the address to connect to. A URI can specify a TCP
           connection (such as "nbd://localhost:10809/export") or a Unix socket (such as
           "nbd+unix:///export?socket=/path/to/sock").  Remember to use proper shell quoting to prevent URI from
           accidentally being handled as a shell glob. The uri parameter is only available when the plugin was
           compiled against libnbd with URI support; "nbdkit --dump-plugin nbd" will contain "libnbd_uri=1" if
           this is the case.

       tls=MODE
           Selects which TLS mode to use with the server. If no other tls option is present, this defaults to
           "off", where the client does not attempt encryption (and may be rejected by a server that requires
           it). If omitted but another tls option is present, this defaults to "on", where the client
           opportunistically attempts a TLS handshake, but will continue running unencrypted if the server does
           not support encryption. If set to "require" or if the "uri" parameter is used with a scheme that
           requires encryption (such as "nbds://host"), then this requires an encrypted connection to the
           server.

           The tls parameter is only available when the plugin was compiled against libnbd with TLS support;
           "nbdkit --dump-plugin nbd" will contain "libnbd_tls=1" if this is the case.  Note the difference
           between "--tls=..." controlling what nbdkit serves, and "tls=..."  controlling what the nbd plugin
           connects to as a client.

       tls-certificates=DIR
           This specifies the directory containing X.509 client certificates to present to the server.

       tls-verify=BOOL
           This defaults to true; setting it to false disables server name verification, which opens you to
           potential Man-in-the-Middle (MITM) attacks, but allows for a simpler setup for distributing
           certificates.

       tls-username=NAME
           If provided, this overrides the user name to present to the server alongside the certificate.

       tls-psk=FILE
           If provided, this is the filename containing the Pre-Shared Keys (PSK) to present to the server.
           While this is easier to set up than X.509, it requires that the PSK file be transmitted over a secure
           channel.

EXAMPLES

       Expose the contents of an export served by an old style server over a Unix socket to TCP network clients
       that only want to consume encrypted data. Use --exit-with-parent to clean up nbdkit at the same time that
       the old server exits.

        ( sock=`mktemp -u`
          nbdkit --exit-with-parent --tls=require nbd socket=$sock &
          exec /path/to/oldserver --socket=$sock )

        ┌────────────┐   TLS    ┌────────┐  plaintext  ┌────────────┐
        │ new client │ ────────▶│ nbdkit │ ───────────▶│ old server │
        └────────────┘   TCP    └────────┘    Unix     └────────────┘

       Combine nbdkit's partition filter with qemu-nbd's ability to visit qcow2 files (nbdkit does not have a
       native qcow2 plugin), performing the same task as the deprecated "qemu-nbd -P 1 -f qcow2
       /path/to/image.qcow2" command. Allow multiple clients, even though "qemu-nbd" without -t normally quits
       after the first client, and utilize a 5-second retry to give qemu-nbd time to create the socket:

        ( sock=`mktemp -u`
          nbdkit --exit-with-parent --filter=partition nbd \
            nbd+unix:///\?socket=$sock shared=1 retry=5 partition=1 &
          exec qemu-nbd -k $sock -f qcow2 /path/to/image.qcow2 )

       Conversely, expose the contents of export foo from a new style server with encrypted data to a client
       that can only consume unencrypted old style. Use --run to clean up nbdkit at the time the client exits.
       In general, note that it is best to keep the plaintext connection limited to a Unix socket on the local
       machine.

        nbdkit -U - -o --tls=off nbd hostname=example.com export=foo tls=require \
         --run '/path/to/oldclient --socket=$unixsocket'

        ┌────────────┐  plaintext  ┌────────┐   TLS    ┌────────────┐
        │ old client │ ───────────▶│ nbdkit │ ────────▶│ new server │
        └────────────┘    Unix     └────────┘   TCP    └────────────┘

       Learn which features are provided by libnbd by inspecting the "libnbd_*" lines:

        nbdkit --dump-plugin nbd

FILES

       $plugindir/nbdkit-nbd-plugin.so
           The plugin.

           Use "nbdkit --dump-config" to find the location of $plugindir.

VERSION

       "nbdkit-nbd-plugin" first appeared in nbdkit 1.2.

SEE ALSO

       nbdkit(1), nbdkit-captive(1), nbdkit-filter(3), nbdkit-tls(1), nbdkit-plugin(3), libnbd(3), qemu-nbd(1).

AUTHORS

       Eric Blake

COPYRIGHT

       Copyright (C) 2017, 2019 Red Hat Inc.

LICENSE

       Redistribution and use in source and binary forms, with or without modification, are permitted provided
       that the following conditions are met:

       •   Redistributions of source code must retain the above copyright notice, this list of conditions and
           the following disclaimer.

       •   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and
           the following disclaimer in the documentation and/or other materials provided with the distribution.

       •   Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote
           products derived from this software without specific prior written permission.

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       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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