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  host  [  port  ] nbd-device [ -sdp ] [ -swap ] [ -persist ] [ -nofork ] [ -block-size block size ] [ -timeout seconds ] [ -name
       name ]

       nbd-client -d nbd-device

       nbd-client -c nbd-device

       nbd-client -l host

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.

       Optionally, long options can also be specified with two leading dashes.

OPTIONS

       The following options are supported:

       -block-size block size

       -b     Use a blocksize of "block size". Default is 1024; allowed values are either 512, 1024, 2048 or 4096

       host   The hostname or IP address of the machine running nbd-server. Since 2.9.15, the NBD utilities support IPv6.

       -timeout seconds

       -t     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.

	      This option is required, unless the -N option is specified.

       nbd-device
	      The block special file this nbd-client should connect to.

       -check

       -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.

       -disconnect

       -d     Disconnect the specified nbd device from the server

       -list

       -l     Ask  the	server	for  a	list  of  available exports. If the server is exporting over IPv6 as well as over IPv4, this will list all
	      exports twice; otherwise, it should list them all only once.

	      Note that this option only works with nbd-server processes running version 3.1 or above, and must be enabled in server configuration
	      (with the "allowlist" option) before it can be used.

       -persist

       -p     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

       -S     Connect to the server using the Socket Direct Protocol (SDP), rather than IP. See nbd-server(5) for details.

       -swap

       -s     Specifies that this NBD device will be used as swapspace. This option attempts to prevent deadlocks  by  performing  mlockall()  and
	      adjusting the oom-killer score at an appropriate time. It does not however guarantee that such deadlocks can be avoided.

       -nofork

       -n     Specifies that the NBD client should not detach and daemonize itself. This is mostly useful for debugging.

	      Note  that  nbd-client will still fork once to trigger an update to the device node's partition table. It is not possible to disable
	      this.

       -name

       -N     Specifies the name of the export that we want to use. Required if the port is not specified, not allowed in the other case.

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/nbd0":

	 nbd-client server.domain.com 2000 /dev/nbd0

       o To connect to a server running on port 2001 at host "swapserver.domain.com", using the client's block special file "/dev/nbd1", for  swap
	 purposes:

	 nbd-client swapserver.domain.com 2001 /dev/nbd1 -swap

       o To disconnect the above connection again (after making sure the block special file is not in use anymore):

	 nbd-client -d /dev/nbd1

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.

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