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.\" ========================================================================
.\"
.IX Title "nbdkit 1"
.TH nbdkit 1 "2016-06-21" "nbdkit" "nbdkit"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
nbdkit \- A toolkit for creating NBD servers
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 4
\& nbdkit [\-\-dump\-config] [\-e EXPORTNAME] [\-f] [\-g GROUP] [\-i IPADDR]
\&        [\-\-newstyle] [\-\-oldstyle] [\-P PIDFILE] [\-p PORT] [\-r]
\&        [\-\-run CMD] [\-s] [\-U SOCKET] [\-u USER] [\-v] [\-V]
\&        PLUGIN [key=value [key=value [...]]]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Network Block Device (\s-1NBD\s0) is a network protocol for accessing block
devices over the network.  Block devices are hard disks and things
that behave like hard disks such as disk images and virtual machines.
.PP
\&\f(CW\*(C`nbdkit\*(C'\fR is both a toolkit for creating \s-1NBD\s0 servers from
\&\*(L"unconventional\*(R" sources and the name of an \s-1NBD\s0 server.
.PP
To create a new Network Block Device source, all you need to do is
write a few glue functions, possibly in C, or perhaps in a high level
language like Perl or Python.  The liberal licensing of nbdkit is
meant to allow you to link nbdkit with proprietary libraries or to
include nbdkit in proprietary code.
.PP
If you want to write an nbdkit plugin, you should read
\&\fInbdkit\-plugin\fR\|(3).
.PP
Several plugins may be found in \f(CW\*(C`$libdir/nbdkit/plugins\*(C'\fR.  You can
give the full path to the plugin, like this:
.PP
.Vb 1
\& nbdkit $libdir/nbdkit/plugins/nbdkit\-file\-plugin.so [...]
.Ve
.PP
but it is usually more convenient to use this equivalent syntax:
.PP
.Vb 1
\& nbdkit file [...]
.Ve
.PP
\&\f(CW$libdir\fR is set at compile time.  To print it out, do:
.PP
.Vb 1
\& nbdkit \-\-dump\-config
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Serve file \f(CW\*(C`disk.img\*(C'\fR on port 10809:
.PP
.Vb 1
\& nbdkit file file=disk.img
.Ve
.PP
Run the example1 plugin and connect to it using \fIguestfish\fR\|(1):
.PP
.Vb 2
\& nbdkit example1
\& guestfish \-\-ro \-a nbd://localhost
.Ve
.PP
Run the example3 plugin and connect to it using \fIguestfish\fR\|(1):
.PP
.Vb 2
\& nbdkit example3 size=1G
\& guestfish \-\-ro \-a nbd://localhost
.Ve
.PP
To display usage information about a specific plugin:
.PP
.Vb 1
\& nbdkit \-\-help example1
.Ve
.SH "GLOBAL OPTIONS"
.IX Header "GLOBAL OPTIONS"
.IP "\fB\-\-help\fR" 4
.IX Item "--help"
Display brief command line usage information and exit.
.IP "\fB\-\-dump\-config\fR" 4
.IX Item "--dump-config"
Dump out the compile-time configuration values and exit.
.IP "\fB\-e\fR \s-1EXPORTNAME\s0" 4
.IX Item "-e EXPORTNAME"
.PD 0
.IP "\fB\-\-export\fR \s-1EXPORTNAME\s0" 4
.IX Item "--export EXPORTNAME"
.IP "\fB\-\-export\-name\fR \s-1EXPORTNAME\s0" 4
.IX Item "--export-name EXPORTNAME"
.IP "\fB\-\-exportname\fR \s-1EXPORTNAME\s0" 4
.IX Item "--exportname EXPORTNAME"
.PD
Set the exportname and use the newstyle protocol (implies \fI\-n\fR).
.Sp
If not set, exportname \f(CW""\fR (empty string) is used.  Exportnames are
not allowed with the oldstyle protocol.
.IP "\fB\-f\fR" 4
.IX Item "-f"
.PD 0
.IP "\fB\-\-foreground\fR" 4
.IX Item "--foreground"
.IP "\fB\-\-no\-fork\fR" 4
.IX Item "--no-fork"
.PD
\&\fIDon't\fR fork into the background.
.IP "\fB\-g\fR \s-1GROUP\s0" 4
.IX Item "-g GROUP"
.PD 0
.IP "\fB\-\-group\fR \s-1GROUP\s0" 4
.IX Item "--group GROUP"
.PD
Change group to \f(CW\*(C`GROUP\*(C'\fR after starting up.  A group name or numeric
group \s-1ID\s0 can be used.
.Sp
The server needs sufficient permissions to be able to do this.
Normally this would mean starting the server up as root.
.Sp
See also \fI\-u\fR.
.IP "\fB\-i\fR \s-1IPADDR\s0" 4
.IX Item "-i IPADDR"
.PD 0
.IP "\fB\-\-ip\-addr\fR \s-1IPADDR\s0" 4
.IX Item "--ip-addr IPADDR"
.IP "\fB\-\-ipaddr\fR \s-1IPADDR\s0" 4
.IX Item "--ipaddr IPADDR"
.PD
Listen on the specified interface.  The default is to listen on all
interfaces.  See also \fI\-p\fR.
.IP "\fB\-n\fR" 4
.IX Item "-n"
.PD 0
.IP "\fB\-\-new\-style\fR" 4
.IX Item "--new-style"
.IP "\fB\-\-newstyle\fR" 4
.IX Item "--newstyle"
.PD
Use the newstyle \s-1NBD\s0 protocol instead of the default (oldstyle)
protocol.  See \*(L"\s-1NEW STYLE VS OLD STYLE PROTOCOL\*(R"\s0 below.
.IP "\fB\-o\fR" 4
.IX Item "-o"
.PD 0
.IP "\fB\-\-old\-style\fR" 4
.IX Item "--old-style"
.IP "\fB\-\-oldstyle\fR" 4
.IX Item "--oldstyle"
.PD
Use the oldstyle \s-1NBD\s0 protocol.  This is currently the default (unless
you use \fI\-n\fR or \fI\-e\fR), so this flag does nothing, but it is possible
we might change the default protocol in future.  See \*(L"\s-1NEW STYLE VS
OLD STYLE PROTOCOL\*(R"\s0 below.
.IP "\fB\-P\fR \s-1PIDFILE\s0" 4
.IX Item "-P PIDFILE"
.PD 0
.IP "\fB\-\-pid\-file\fR \s-1PIDFILE\s0" 4
.IX Item "--pid-file PIDFILE"
.IP "\fB\-\-pidfile\fR \s-1PIDFILE\s0" 4
.IX Item "--pidfile PIDFILE"
.PD
Write \f(CW\*(C`PIDFILE\*(C'\fR (containing the process \s-1ID\s0 of the server) after
nbdkit becomes ready to accept connections.
.Sp
If the file already exists, it is overwritten.  nbdkit \fIdoes not\fR
delete the file when it exits.
.IP "\fB\-p\fR \s-1PORT\s0" 4
.IX Item "-p PORT"
.PD 0
.IP "\fB\-\-port\fR \s-1PORT\s0" 4
.IX Item "--port PORT"
.PD
Change the \s-1TCP/IP\s0 port number on which nbdkit serves requests.
The default is \f(CW10809\fR.  See also \fI\-i\fR.
.IP "\fB\-r\fR" 4
.IX Item "-r"
.PD 0
.IP "\fB\-\-read\-only\fR" 4
.IX Item "--read-only"
.IP "\fB\-\-readonly\fR" 4
.IX Item "--readonly"
.PD
The export will be read-only.  If a client writes, then it will get an
error.
.Sp
Note that some plugins inherently don't support writes.  With those
plugins the \fI\-r\fR option is added implicitly.
.Sp
Copy-on-write (or \*(L"snapshot\*(R") functionality is not supported by this
server.  However if you are using qemu as a client (or indirectly via
libguestfs) then it supports snapshots.
.IP "\fB\-\-run\fR \s-1CMD\s0" 4
.IX Item "--run CMD"
Run nbdkit as a captive subprocess of \f(CW\*(C`CMD\*(C'\fR.  When \f(CW\*(C`CMD\*(C'\fR exits,
nbdkit is killed.  See \*(L"\s-1CAPTIVE NBDKIT\*(R"\s0 below.
.Sp
This option implies \fI\-\-foreground\fR.
.IP "\fB\-s\fR" 4
.IX Item "-s"
.PD 0
.IP "\fB\-\-single\fR" 4
.IX Item "--single"
.IP "\fB\-\-stdin\fR" 4
.IX Item "--stdin"
.PD
Don't fork.  Handle a single \s-1NBD\s0 connection on stdin/stdout.  After
stdin closes, the server exits.
.Sp
You can use this option to run nbdkit from inetd, systemd or similar
superservers; or just for testing; or if you want to run nbdkit in a
non-conventional way.
.Sp
This option implies \fI\-\-foreground\fR.
.IP "\fB\-U\fR \s-1SOCKET\s0" 4
.IX Item "-U SOCKET"
.PD 0
.IP "\fB\-\-unix\fR \s-1SOCKET\s0" 4
.IX Item "--unix SOCKET"
.IP "\fB\-U \-\fR" 4
.IX Item "-U -"
.IP "\fB\-\-unix \-\fR" 4
.IX Item "--unix -"
.PD
Accept connections on the Unix domain socket \f(CW\*(C`SOCKET\*(C'\fR (which is a
path).
.Sp
nbdkit creates this socket, but it will probably have incorrect
permissions (too permissive).  If it is a problem that some
unauthorized user could connect to this socket between the time that
nbdkit starts up and the authorized user connects, then put the socket
into a directory that has restrictive permissions.
.Sp
nbdkit does \fBnot\fR delete the socket file when it exits.  The caller
should delete the socket file after use (else if you try to start
nbdkit up again you will get an \f(CW\*(C`Address already in use\*(C'\fR error).
.Sp
If the socket name is \fI\-\fR then nbdkit generates a randomly named
private socket.  This is useful with \*(L"\s-1CAPTIVE NBDKIT\*(R"\s0.
.IP "\fB\-u\fR \s-1USER\s0" 4
.IX Item "-u USER"
.PD 0
.IP "\fB\-\-user\fR \s-1USER\s0" 4
.IX Item "--user USER"
.PD
Change user to \f(CW\*(C`USER\*(C'\fR after starting up.  A user name or numeric user
\&\s-1ID\s0 can be used.
.Sp
The server needs sufficient permissions to be able to do this.
Normally this would mean starting the server up as root.
.Sp
See also \fI\-g\fR.
.IP "\fB\-v\fR" 4
.IX Item "-v"
.PD 0
.IP "\fB\-\-verbose\fR" 4
.IX Item "--verbose"
.PD
Enable verbose messages.
.Sp
It's a good idea to use \fI\-f\fR as well so the process does not fork
into the background (but not required).
.IP "\fB\-V\fR" 4
.IX Item "-V"
.PD 0
.IP "\fB\-\-version\fR" 4
.IX Item "--version"
.PD
Print the version number of nbdkit and exit.
.SH "PLUGIN CONFIGURATION"
.IX Header "PLUGIN CONFIGURATION"
After specifying the plugin name you can (optionally, it depends
on the plugin) give plugin configuration on the command line in
the form of \f(CW\*(C`key=value\*(C'\fR.  For example:
.PP
.Vb 1
\& nbdkit file file=disk.img
.Ve
.PP
To list all the options supported by a plugin, do:
.PP
.Vb 1
\& nbdkit \-\-help file
.Ve
.SH "CAPTIVE NBDKIT"
.IX Header "CAPTIVE NBDKIT"
You can run nbdkit as a \*(L"captive process\*(R", using the \fI\-\-run\fR option.
This means that nbdkit runs as long as (for example) \fIqemu\fR\|(1) or
\&\fIguestfish\fR\|(1) is running.  When those exit, nbdkit is killed.
.PP
Some examples should make this clear.
.PP
To run nbdkit captive under qemu:
.PP
.Vb 1
\& nbdkit file file=disk.img \-\-run \*(Aqqemu \-drive file=$nbd,if=virtio\*(Aq
.Ve
.PP
On the qemu command line, \f(CW$nbd\fR is substituted automatically with
the right \s-1NBD\s0 path so it can connect to nbdkit.  When qemu exits,
nbdkit is killed and cleaned up automatically.
.PP
Running nbdkit captive under guestfish:
.PP
.Vb 1
\& nbdkit file file=disk.img \-\-run \*(Aqguestfish \-\-format=raw \-a $nbd \-i\*(Aq
.Ve
.PP
When guestfish exits, nbdkit is killed.
.PP
The following shell variables are available in the \fI\-\-run\fR argument:
.ie n .IP "$nbd" 4
.el .IP "\f(CW$nbd\fR" 4
.IX Item "$nbd"
A \s-1URL\s0 that refers to the nbdkit port or socket.
.Sp
Note there is some magic here, since qemu and guestfish URLs have a
different format, so nbdkit tries to guess which you are running.  If
the magic doesn't work, try using the variables below instead.
.ie n .IP "$port" 4
.el .IP "\f(CW$port\fR" 4
.IX Item "$port"
If ≠ "", the port number that nbdkit is listening on.
.ie n .IP "$unixsocket" 4
.el .IP "\f(CW$unixsocket\fR" 4
.IX Item "$unixsocket"
If ≠ "", the Unix domain socket that nbdkit is listening on.
.PP
\&\fI\-\-run\fR implies \fI\-\-foreground\fR.  It is not possible, and probably
not desirable, to have nbdkit fork into the background when using
\&\fI\-\-run\fR.
.PP
Even when running captive, nbdkit still listens on the regular \s-1TCP/IP\s0
port, unless you specify the \fI\-p\fR/\fI\-U\fR options.  If you want a truly
private captive nbdkit, then you should create a private random
Unix socket, like this:
.PP
.Vb 1
\& nbdkit \-U \- plugin [args] \-\-run \*(Aq...\*(Aq
.Ve
.SH "NEW STYLE VS OLD STYLE PROTOCOL"
.IX Header "NEW STYLE VS OLD STYLE PROTOCOL"
The \s-1NBD\s0 protocol comes in two incompatible forms that we call
\&\*(L"oldstyle\*(R" and \*(L"newstyle\*(R".  Unfortunately which protocol you should
use depends on the client and cannot be known in advance, nor can it
be negotiated from the server side.
.PP
nbdkit currently defaults to the oldstyle protocol for compatibility
with qemu and libguestfs.  This is also the same behaviour as qemu-nbd
≤ 2.5.  Use the \fI\-n\fR or \fI\-\-newstyle\fR flag on the command line to
use the newstyle protocol.  Use the \fI\-e\fR or \fI\-\-exportname\fR flag to
set the exportname for the newstyle protocol.  Use the \fI\-o\fR or
\&\fI\-\-oldstyle\fR flag to force the oldstyle protocol.
.PP
Some common clients and the protocol they require:
.PP
.Vb 7
\& Client                          Protocol
\& \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\& qemu <= 2.5 without exportname  oldstyle
\& qemu <= 2.5 with exportname     newstyle
\& qemu >= 2.6                     client can talk either protocol
\& nbd\-client < 3.10               client can talk either protocol
\& nbd\-client >= 3.10              newstyle
.Ve
.PP
If you use qemu ≤ 2.5 without the exportname field against a
newstyle server, it will give the error:
.PP
.Vb 1
\& Server requires an export name
.Ve
.PP
If you use qemu ≤ 2.5 with the exportname field against an
oldstyle server, it will give the error:
.PP
.Vb 1
\& Server does not support export names
.Ve
.PP
If you use the oldstyle protocol with nbd-client ≥ 3.10, it will
give the error:
.PP
.Vb 1
\& Error: It looks like you\*(Aqre trying to connect to an oldstyle server.
.Ve
.PP
If you want to claim compatibility with what the \s-1NBD\s0 proto.txt
document says should be the case (which isn't based in reality), then
you should always use newstyle when using port 10809, and use oldstyle
on all other ports.
.SH "SIGNALS"
.IX Header "SIGNALS"
\&\f(CW\*(C`nbdkit\*(C'\fR responds to the following signals:
.ie n .IP """SIGINT""" 4
.el .IP "\f(CWSIGINT\fR" 4
.IX Item "SIGINT"
.PD 0
.ie n .IP """SIGQUIT""" 4
.el .IP "\f(CWSIGQUIT\fR" 4
.IX Item "SIGQUIT"
.ie n .IP """SIGTERM""" 4
.el .IP "\f(CWSIGTERM\fR" 4
.IX Item "SIGTERM"
.PD
The server exits cleanly.
.ie n .IP """SIGPIPE""" 4
.el .IP "\f(CWSIGPIPE\fR" 4
.IX Item "SIGPIPE"
This signal is ignored.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fInbdkit\-plugin\fR\|(3),
\&\fInbdkit\-curl\-plugin\fR\|(1),
\&\fInbdkit\-example1\-plugin\fR\|(1),
\&\fInbdkit\-example2\-plugin\fR\|(1),
\&\fInbdkit\-example3\-plugin\fR\|(1),
\&\fInbdkit\-file\-plugin\fR\|(1),
\&\fInbdkit\-gzip\-plugin\fR\|(1),
\&\fInbdkit\-libvirt\-plugin\fR\|(1),
\&\fInbdkit\-ocaml\-plugin\fR\|(3),
\&\fInbdkit\-perl\-plugin\fR\|(3),
\&\fInbdkit\-python\-plugin\fR\|(3),
\&\fInbdkit\-vddk\-plugin\fR\|(1).
\&\fInbdkit\-xz\-plugin\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Richard W.M. Jones
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2013 Red Hat Inc.
.SH "LICENSE"
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP "\(bu" 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP "\(bu" 4
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.
.IP "\(bu" 4
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.
.PP
\&\s-1THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS \s0''\s-1AS IS\s0'' \s-1AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES \s0(\s-1INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES\s0; \s-1LOSS OF
USE, DATA, OR PROFITS\s0; \s-1OR BUSINESS INTERRUPTION\s0) \s-1HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT \s0(\s-1INCLUDING NEGLIGENCE OR OTHERWISE\s0) \s-1ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.\s0