XNBD-CLIENT(1) General Commands Manual XNBD-CLIENT(1)
NAME
xnbd-client -- connect to a server running xnbd-server(8), to use its exported block device
SYNOPSIS
xnbd-client [--blocksize SIZE] [--connect] [--exportname NAME] [--recovery-command COMMAND] [--recovery-command-reboot COMMAND]
[--retry COUNT] [--timeout SECONDS] NBD-DEVICE [ HOST PORT ...]
xnbd-client [bs=SIZE] [timeout=SECONDS] HOST PORT NBD-DEVICE
xnbd-client --disconnect NBD-DEVICE
xnbd-client --check NBD-DEVICE
DESCRIPTION
With xnbd-client, you can connect to a server running xnbd-server or xnbd-wrapper, thus using raw diskspace from that server as a blockde-
vice 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.
Long options can also be specified with two leading dashes. Some options are call compatible to nbd-client(1) as are most behavioural
switches. This makes xnbd-client a plug-in replacement for nbd-client.
OPTIONS
The following options are supported:
--blocksize SIZE
Use the provided value as block size. Default is 1024; allowed values are either 512, 1024, 2048 or 4096. For best results use
a block size value of 4096
For compatibility to nbd-client(1) you can also use bs=SIZE
--check|-c
Check whether the specified nbd device is connected.
If the device is connected, xnbd-client will exit with an exit state of 0 and print the PID of the xnbd-client instance that con-
nected it to stdout.
If the device is not connected or does not exist (for example because the nbd module was not loaded), xnbd-client will exit with
an exit state of 1 and not print anything on stdout.
If an error occurred, xnbd-client will exit with an exit state of 2, and not print anything on stdout either.
--connect|-C
Connect to the nbd-server
--disconnect|-d
Disconnect the specified nbd device from the server. Terminates execution with an exit state of 0 on success.
--exportname NAME
If the server supports to access devices by an identifier, use NAME to request access to a particular volume. This command is
useful in combination with a xnbd-wrapper and only succeeds, if the remote host is exporting the requested device.
--retry COUNT
Try up to "COUNT" times to connect to the associated nbd-server. Default is 1, that is nbd-client will stop after the first
unsuccessful try.
--recovery-command
invoke a specified command "COMMAND" on unexpected disconnection
--recovery-command-reboot
Invoke the reboot(8) command on unexpected disconnection
--timeout SECONDS
Use a timeout period (default is 0 which means not to use a timeout). Please do not use this option for now, as it seems not to
work due to a bug in the kernel module.
For compatibility to nbd-client(1) you can also use timeout=SECONDS
POSITIONAL ARGUMENTS
The following positional options are supported:
HOST The site to connect to a remote xnbd-server. You can specify any resolvable hostname, IPv4 or IPv6 address.
PORT The port number to connect to on remote side
NBD-DEVICE
The local nbd-device to be associated with the remote xnbd-server.
You can specify multiple host port tuples. xnbd-client will try to connect to each of them in order until it succeeds to establish a
connection to a server.
BUGS
The NBD device is known to deadlock when not being used altogether with the deadline scheduler. Make sure to do:
echo deadline > /sys/block/nbd0/queue/scheduler
SEE ALSO
xnbd-server (8), xnbd-wrapper (8).
AUTHOR
The NBD kernel module and the NBD tools have been written by Pavel Macheck (pavel@ucw.cz) and is now maintained by Paul Clements.
(Paul.Clements@steeleye.com).
The xNBD userland (client and server) have been written by Takahiro Hirofuchi (t.hirofuchi@aist.go.jp)
This manual page was written by Arno Toell (debian@toell.net) for the Debian GNU/Linux system (but may be used by others). Large parts are
verbatim copies of the original nbd-server and nbd-client manual pages written by Wouter Verhelst (wouter@debian.org). Permission 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.
XNBD-CLIENT(1)