NAME¶
nbdkit - A toolkit for creating NBD servers
SYNOPSIS¶
nbdkit [--dump-config] [-f] [-g GROUP] [-i IPADDR]
[-P PIDFILE] [-p PORT] [-r] [--run CMD] [-s]
[-U SOCKET] [-u USER] [-v] [-V]
PLUGIN [key=value [key=value [...]]]
DESCRIPTION¶
"nbdkit" is both a toolkit for creating Network Block Device (NBD)
servers from "unconventional" sources and the name of an NBD server.
To create a new block device source, all you have to do is write a few glue
functions. The liberal licensing of nbdkit is meant to allow you to link
nbdkit with proprietary libraries or include nbdkit in proprietary code.
If you want to write an nbdkit plugin, you should read
nbdkit-plugin(3).
Several plugins may be found in "$libdir/nbdkit/plugins". You can give
the full path to the plugin, like this:
nbdkit $libdir/nbdkit/plugins/nbdkit-file-plugin.so [...]
but it is usually more convenient to use this equivalent syntax:
nbdkit file [...]
$libdir is set at compile time. To print it out, do:
nbdkit --dump-config
EXAMPLES¶
Serve file "disk.img" on port 10809:
nbdkit file file=disk.img
Run the example1 plugin and connect to it using
guestfish(1):
nbdkit example1
guestfish --ro -a nbd://localhost
Run the example3 plugin and connect to it using
guestfish(1):
nbdkit example3 size=1G
guestfish --ro -a nbd://localhost
To display usage information about a specific plugin:
nbdkit --help example1
GLOBAL OPTIONS¶
- --help
- Display brief command line usage information and exit.
- --dump-config
- Dump out the compile-time configuration values and exit.
- -f
- --foreground
- --no-fork
- Don't fork into the background.
- -g GROUP
- --group GROUP
- Change group to "GROUP" after starting up. A group name or
numeric group ID can be used.
The server needs sufficient permissions to be able to do this. Normally this
would mean starting the server up as root.
See also -u.
- -i IPADDR
- --ip-addr IPADDR
- --ipaddr IPADDR
- Listen on the specified interface. The default is to listen on all
interfaces. See also -p.
- -P PIDFILE
- --pid-file PIDFILE
- --pidfile PIDFILE
- Write "PIDFILE" (containing the process ID of the server) after
nbdkit becomes ready to accept connections.
If the file already exists, it is overwritten. nbdkit does not delete
the file when it exits.
- -p PORT
- --port PORT
- Change the TCP/IP port number on which nbdkit serves requests. The default
is 10809. See also -i.
- -r
- --read-only
- --readonly
- The export will be read-only. If a client writes, then it will get an
error.
Note that some plugins inherently don't support writes. With those plugins
the -r option is added implicitly.
Copy-on-write (or "snapshot") functionality is not supported by
this server. However if you are using qemu as a client (or indirectly via
libguestfs) then it supports snapshots.
- --run CMD
- Run nbdkit as a captive subprocess of "CMD". When
"CMD" exits, nbdkit is killed. See "CAPTIVE NBDKIT"
below.
This option implies --foreground.
- -s
- --single
- --stdin
- Don't fork. Handle a single NBD connection on stdin/stdout. After stdin
closes, the server exits.
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.
This option implies --foreground.
- -U SOCKET
- --unix SOCKET
- -U -
- --unix -
- Accept connections on the Unix domain socket "SOCKET" (which is
a path).
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.
nbdkit does not 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 "Address already in use" error).
If the socket name is - then nbdkit generates a randomly named
private socket. This is useful with "CAPTIVE NBDKIT".
- -u USER
- --user USER
- Change user to "USER" after starting up. A user name or numeric
user ID can be used.
The server needs sufficient permissions to be able to do this. Normally this
would mean starting the server up as root.
See also -g.
- -v
- --verbose
- Enable verbose messages.
It's a good idea to use -f as well so the process does not fork into
the background (but not required).
- -V
- --version
- Print the version number of nbdkit and exit.
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
"key=value". For example:
nbdkit file file=disk.img
To list all the options supported by a plugin, do:
nbdkit --help file
CAPTIVE NBDKIT¶
You can run nbdkit as a "captive process", using the
--run
option. This means that nbdkit runs as long as (for example)
qemu(1) or
guestfish(1) is running. When those exit, nbdkit is killed.
Some examples should make this clear.
To run nbdkit captive under qemu:
nbdkit file file=disk.img --run 'qemu -drive file=$nbd,if=virtio'
On the qemu command line, $nbd is substituted automatically with the right NBD
path so it can connect to nbdkit. When qemu exits, nbdkit is killed and
cleaned up automatically.
Running nbdkit captive under guestfish:
nbdkit file file=disk.img --run 'guestfish --format=raw -a $nbd -i'
When guestfish exits, nbdkit is killed.
The following shell variables are available in the
--run argument:
- $nbd
- A URL that refers to the nbdkit port or socket.
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.
- $port
- If ≠ "", the port number that nbdkit is listening
on.
- $unixsocket
- If ≠ "", the Unix domain socket that nbdkit is listening
on.
--run implies
--foreground. It is not possible, and probably not
desirable, to have nbdkit fork into the background when using
--run.
Even when running captive, nbdkit still listens on the regular TCP/IP port,
unless you specify the
-p/
-U options. If you want a truly
private captive nbdkit, then you should create a private random Unix socket,
like this:
nbdkit -U - plugin [args] --run '...'
SIGNALS¶
"nbdkit" responds to the following signals:
- "SIGINT"
- "SIGQUIT"
- "SIGTERM"
- The server exits cleanly.
- "SIGPIPE"
- This signal is ignored.
SEE ALSO¶
nbdkit-plugin(3),
nbdkit-curl-plugin(1),
nbdkit-example1-plugin(1),
nbdkit-example2-plugin(1),
nbdkit-example3-plugin(1),
nbdkit-file-plugin(1),
nbdkit-gzip-plugin(1),
nbdkit-libvirt-plugin(1),
nbdkit-perl-plugin(3),
nbdkit-python-plugin(3),
nbdkit-vddk-plugin(1).
nbdkit-xz-plugin(1).
AUTHORS¶
Richard W.M. Jones
COPYRIGHT¶
Copyright (C) 2013 Red Hat Inc.
LICENSE¶
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are permitted provided that the following conditions are met:
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