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

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