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       nbd-client  -  connect  to  a  server running nbd-server(1), to use its
       exported block device


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

       nbd-client -d nbd-device

       nbd-client -c nbd-device

       nbd-client -l host [ port ]


       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

       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.


       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.

              For the deprecated oldstyle protocol, passing a port  number  is
              required.  In  the oldstyle protocol, exports are defined by the
              port on which they are running.

              For the newstyle protocol, the port number  defaults  to  10809,
              the  IANA-assigned  port  number  for  the  NBD  protocol.   The
              newstyle protocol is selected automatically by  nbd-client  when
              one of the -list or -name options are used.

              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


       -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


       -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.


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


       -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.


       -m     The systemd init system requires that processes which should not
              be killed at shutdown time be marked appropriately by  replacing
              the first letter of their argv[0] with an '@' sign.

              This option will cause nbd-client to do so.

              Note  that  this only works if nbd-client is run from an initrd;
              i.e., systemd will ignore such a mark if run from a systemd unit
              file or from the command line.


       -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.


       -N     Specifies the name of the export that we want to use.   Required
              if  the  port  is  not  specified;  changes the default port for
              newstyle negotiation from 10809 in the other case.

              When this option is  specified,  nbd-client  uses  the  newstyle
              version  of  the negotiation protocol. This version is much more
              flexible than the oldstyle negotiation, and should be  used  for
              new configurations.


       Some examples of nbd-client usage:

       · To   connect   to   a   server   running   on   port   2000  at  host
         "",  using   the   client's   block   special   file

         nbd-client 2000 /dev/nbd0

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

         nbd-client 2001 /dev/nbd1 -swap

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

         nbd-client -d /dev/nbd1


       nbd-server (1).


       The NBD kernel module and the NBD tools  have  been  written  by  Pavel
       Macheck (

       The    kernel    module    is   now   maintained   by   Paul   Clements
       (, while the userland tools  are  maintained
       by Wouter Verhelst (

       This  manual  page was written by Wouter Verhelst (<>)
       for  the  Debian  GNU/Linux  system  (but  may  be  used  by   others).
       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.

                                       $                         NBD-CLIENT(8)

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