nbdsh(1)

NAME

nbdsh - network block device (NBD) shell

SYNOPSIS

 $ nbdsh
 Welcome to nbdsh, the shell for interacting with
 Network Block Device (NBD) servers.
 The ‘nbd’ module has already been imported and there
 is an open NBD handle called ‘h’.
 nbd> h.connect_command(["nbdkit", "-s", "memory", "1G"])
 nbd> h.get_size()
 1073741824
 nbd> buf = b"hello, world"
 nbd> h.pwrite(buf, 0)
 nbd> exit()

DESCRIPTION

nbdsh is a Python-based interactive shell for accessing Network Block Device (NBD) servers.

For documentation about the libnbd API please open the shell and type:

 help(nbd)

For an introduction to using libnbd from Python see libnbd-python(3).

EXAMPLES

There are other example scripts in the libnbd source repository under sh/examples or see https://gitlab.com/nbdkit/libnbd/tree/master/sh/examples.

Print the size of an NBD export

The -u option connects to an NBD URI. The -c option lets you execute single Python statements from the command line. Combining these two options lets you print the size in bytes of an NBD export:

 $ nbdsh -u nbd://localhost -c 'print(h.get_size())'
 1073741824

Hexdump the boot sector of an NBD export

Using -c - you can feed a whole Python program to the standard input of nbdsh:

 nbdsh -c - <<'EOF'
 from subprocess import *
 h.connect_uri("nbd://localhost")
 bootsect = h.pread(512, 0)
 p = Popen("hexdump -C", shell=True, stdin=PIPE)
 p.stdin.write(bootsect)
 EOF

nbddump(1) is another tool for hexdumping NBD exports.

Overwrite part of the disk with a pattern

Overwrite 2048 bytes, starting at offset 1024 (hex 0x400), with the repeating binary pattern 01010101 10101010. (This operation is destructive!)

 $ nbdkit memory 4096
 $ nbdsh -u nbd://localhost -c 'h.pwrite(b"\x55\xAA" * 1024, 0x400)'
 $ nbddump nbd://localhost
 0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │················│
 ☆
 0400: 55 aa 55 aa 55 aa 55 aa 55 aa 55 aa 55 aa 55 aa │U·U·U·U·U·U·U·U·│
 ☆
 0c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │················│
 ☆
 0ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │················│
 $ killall nbdkit

The -c parameter contains a Python expression which builds a bytearray containing the two byte pattern repeated 1024 times (length 2048 bytes), and calls the Python binding of nbd_pwrite(3). The second parameter is the offset to start writing from. For information about nbdkit, see nbdkit(1) and nbdkit-memory-plugin(1).

OPTIONS

-h

--help: Display brief command line help and exit.

--base-allocation: Request the use of the "base:allocation" meta context, which is the most common context used with nbd_block_status_64(3). This is equivalent to calling "h.set_meta_context(nbd.CONTEXT_BASE_ALLOCATION)" in the shell prior to connecting, and works even when combined with "--uri" (while attempting the same with "-c" would be too late).

-c 'COMMAND ...'

--command 'COMMAND ...': Instead of starting an interactive shell, run a command. This option can be specified multiple times in order to run multiple commands.

-c -

--command -: Read standard input and execute it as a command.

-n: Do not create the implicit handle "h".

--opt-mode: Request that option mode be enabled, which gives fine-grained control over option negotiation after initially contacting the server but prior to actually using the export. This is equivalent to calling "h.set_opt_mode(True)" in the shell prior to connecting, and works even when combined with "--uri" (while attempting the same with "-c" would be too late).

-u URI

--uri URI

Connect to the given NBD URI. This is equivalent to the "h.connect_uri(URI)" command in the shell.

Note that the connection is created prior to processing any "-c" commands, which prevents the use of configuration commands such as "h.add_meta_context("NAME")" from the command line when mixed with this option. The options "--opt-mode" and "--base-allocation" can be used to make this situation easier to manage.

-v

--verbose: Enable verbose libnbd messages. This has the same effect as setting the environment variable "LIBNBD_DEBUG=1"

-V

--version: Display the package name and version and exit.

AUTHORS

Richard W.M. Jones

COPYRIGHT

Copyright Red Hat

LICENSE

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA