NBD-CLIENT(8) NBD-CLIENT(8)
NAME
nbd-client - connect to a server running nbd-server(1), to use its exported block device
SYNOPSIS
nbd-client [ bs=blocksize ] [ timeout=seconds ] host port nbd-device [ -sdp ] [ -swap ] [ -persist ] [ -nofork ]
nbd-client -d nbd-device
nbd-client -c nbd-device
DESCRIPTION
With nbd-client, you can connect to a server running nbd-server, thus using raw diskspace from that server as a blockdevice on the local
client.
To do this, support from the Linux Kernel is necessary, in the form of the Network Block Device (NBD). When you have that, either in the
kernel, or as a module, you can connect to an NBD server and use its exported file through a block special file with major mode 43.
OPTIONS
The following options are supported:
bs=blocksize
Use a blocksize of "blocksize". Default is 1024; allowed values are either 512, 1024, 2048 or 4096
host The hostname of the machine running nbd-server.
timeout=seconds
Set the connection timeout to "seconds". For this to work, you need a kernel with support for the NBD_SET_TIMEOUT ioctl; this was
introduced into Linus' tree on 2007-10-11, and will be part of kernel 2.6.24.
port The TCP port on which nbd-server is running at the server.
nbd-device
The block special file this nbd-client should connect to.
-c Check whether the specified nbd device is connected.
If the device is connected, nbd-client will exit with an exit state of 0 and print the PID of the nbd-client instance that connected
it to stdout.
If the device is not connected or does not exist (for example because the nbd module was not loaded), nbd-client will exit with an
exit state of 1 and not print anything on stdout.
If an error occurred, nbd-client will exit with an exit state of 2, and not print anything on stdout either.
-d Disconnect the specified nbd device from the server
-persist
When this option is specified, nbd-client will immediately try to reconnect an nbd device if the connection ever drops unexpectedly
due to a lost server or something similar.
-sdp Connect to the server using the Socket Direct Protocol (SDP), rather than IP. See nbd-server(1) for details.
-swap Specifies that this NBD device will be used as swapspace. This option attempts to prevent deadlocks by performing mlockall() at an
appropriate time. It does not however guarantee that such deadlocks can be avoided.
-nofork
Specifies that the NBD client should not detach and daemonize itself. This is mostly useful for debugging.
EXAMPLES
Some examples of nbd-client usage:
o To connect to a server running on port 2000 at host "server.domain.com", using the client's block special file "/dev/nb0":
nbd-client server.domain.com 2000 /dev/nb0
o To connect to a server running on port 2001 at host "swapserver.domain.com", using the client's block special file "/dev/nb1", for swap
purposes:
nbd-client swapserver.domain.com 2001 /dev/nb1 -swap
o To disconnect the above connection again (after making sure the block special file is not in use anymore):
nbd-client -d /dev/nb1
SEE ALSO
nbd-server (1).
AUTHOR
The NBD kernel module and the NBD tools have been written by Pavel Macheck (pavel@ucw.cz).
The kernel module is now maintained by Paul Clements (Paul.Clements@steeleye.com), while the userland tools are maintained by Wouter Ver-
helst (wouter@debian.org)
This manual page was written by Wouter Verhelst (<wouter@debian.org>) for the Debian GNU/Linux system (but may be used by others). Permis-
sion is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, version 2, as published
by the Free Software Foundation.
26 May 2009 NBD-CLIENT(8)