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

Provided by: nbd-client_3.7-1ubuntu0.1_amd64

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 [ port ]

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.

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.

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;
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.

EXAMPLES

       Some examples of nbd-client usage:

       • 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

       • 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

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

         nbd-client -d /dev/nbd1

AUTHOR