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.TH "NBD-SERVER" "1" "$Date$" "" ""

.SH NAME
nbd-server \- serve a file as a block device to other computers    running the GNU/Linux(tm) or GNU/Hurd Operating    System
.SH SYNOPSIS

\fBnbd-server \fR \fB\fI[ip@]port\fB\fR \fB\fIfilename\fB\fR [ \fB\fIsize\fB\fR ] [ \fB-r\fR ] [ \fB-m\fR ] [ \fB-c\fR ] [ \fB-l \fIhost list filename\fB\fR ] [ \fB-o \fIsection name\fB\fR ] [ \fB-C \fIconfig file\fB\fR ] [ \fB-M \fImax connections\fB\fR ] [ \fB-V\fR ] [ \fB-n\fR ] [ \fB-d\fR ]

.SH "DESCRIPTION"
.PP
\fBnbd-server\fR is the server for the Linux
Network Block Device (NBD). With NBD, a client can use a file,
exported over the network from a server, as a block device. It can
then be used for whatever purpose a normal block device (harddisk,
CD-ROM, ...) can be used for.
.PP
NBD can be useful for diskless clients that need swapspace,
but you can also create a filesystem on it and use it as though it
were a local filesystem.
.PP
\fBnbd-server\fR implements some security
through a file called "/etc/nbd-server/allow" (by default; a
different file can be chosen with the '-l' option or through a
config file specification). This file must list the IP-addresses or
network masks of clients that are allowed to connect. If it does not
exist, all clients are able to connect. If the file is empty, no
clients can connect.
.PP
Note that while the command line allows for specifying an
export, the use of this option is deprecated. It is preferred to
make use of a configuration file instead, the format of which is
defined in nbd-server(5).
.PP
While nbd-server is running, new exports can be added by
re-writing configuration files and then sending SIGHUP to
nbd-server. SIGHUP causes nbd-server to re-read its configuration
files and to start serving all new exports which were not served
earlier. Reconfiguration does not modify any existing export, it only
appends new ones.
.SH "OPTIONS"
.TP
\fBip\fR
The ip address the server should listen on. This may
be an IPv4 address, an IPv6 address, or a hostname. In the
latter case, nbd-server will do a hostname lookup for the
name specified, and will listen on the first address that is
returned. For compatibility with past versions of
nbd-server, if an IPv4 address is specified, the @ sign that
serves as separator between the address and port may be
replaced by a colon.

If this parameter is not specified, nbd-server will
listen on all local addresses on both IPv4 and IPv6. To
limit to IPv4, specify the address as 0.0.0.0; to limit to
IPv6, specify it as ::.
.TP
\fBport \fR
The port the server should listen to. A valid port is
any number between 1 and 65536; if 0 is used, nbd-server
will listen on stdin (so that nbd-server can be ran from
inetd)
.TP
\fBfilename\fR
The filename of the file that should be exported. This
can be any file, including "real" blockdevices (i.e. a file
from /dev). If the filename includes the literal string
"%s", then this %s will be substituded with the IP-address
of the client trying to connect.
.TP
\fBsize\fR
The size of the block device at the client side. This
is especially useful in conjunction with the -m
option

Can optionally be followed by one of K,k,M or
m, in which case the size will be multiplied by 1024 (K
or k) or 1048576 (M or m)
.TP
\fB-r\fR
Export the file read-only. If a client tries to write
to a read-only exported file, it will receive an error, but
the connection will stay up.
.TP
\fB-m\fR
Work with multiple files. This can be used to export
blockdevices that are larger than the maximum allowed
filesize on a given filesystem; i.e. when the filesystem
does not allow files larger than 2GB (which is true for
Linux 2.2 and below), you can use this option to store the
data in multiple files and export a larger filesystem, if
needed.

To use this option, you must create a number of files
with names in the format "name.X", where "name" is given as
the filename argument to nbd-server, and "X" is a number
starting by 0 and going up for each file.

Allowing more flexibility for this option is planned for
future versions.
.TP
\fB-c\fR
Copy on write. When this option is provided,
write-operations are not done to the exported file, but to a
separate file. This separate file is removed when the
connection is closed, which means that serving this way will
make nbd-server slow down (especially on large block devices
with lots of writes), and that after disconnecting and
reconnecting the client or the server, all changes are
lost.
.TP
\fB-C\fR
Specify configuration file. The default configuration
file, if this parameter is not specified, is
\fI/etc/nbd-server/config\fR\&.

Note that the configuration file is always parsed and
the entries in the file used, even if an extra server is
specified on the command line. To disable the configuration
file entirely, either move it away or use the -C option to
point \fBnbd-server\fR(1) to a non-existing or
empty configuration file.

Also note that if an empty, incomplete, or invalid
configuration file is specified, nbd-server will produce a
warning about failure to parse the config file. If the
command line contains a fully specified configuration, this
warning is harmless and may be ignored.
.TP
\fB-M\fR
Specify the maximum number of opened connections. If this
parameter is not specified, no limit is set.
.TP
\fB-V\fR
Output the version of nbd-server, and exit.
.TP
\fB-n\fR
Do not daemonize the main process. In contrast
to \fB-d\fR, this still allows to fork the
serving process for a client from the main process.
.TP
\fB-d\fR
Do not fork. Useful for debugging.
Implies \fB-n\fR\&.
.TP
\fBhost list filename\fR
This argument should contain a list of IP-addresses
for hosts that may connect to the server. Wildcards are
\fBnot\fR allowed. If the file does not
exist, it is ignored (and any host can connect); If the file
does exist, but is empty, no host can connect. By default,
the name 'nbd_server.allow' is used, and looked for in the
current directory, unless nbd-server is compiled as a
daemon, in which case it is looked for in the
root-directory.
.TP
\fBsection name\fR
If the \fB-o\fR argument is given on the
command line, then nbd-server will output a configuration
file section with this as the header that is functionally
equivalent to the other options specified on the command line,
and exit. This is useful for migrating pre-2.9 nbd-server
initscript configuration files to the new format.
.SH "EXAMPLES"
.PP
Some examples of nbd-server usage:
.TP 0.2i
\(bu
To export a file /export/nbd/exp-bl-dev on port 2000:

\fBnbd-server 2000 /export/nbd/exp-bl-dev\fR
.TP 0.2i
\(bu
To export a the same file read-only:

\fBnbd-server 2000 /export/nbd/exp-bl-dev -r\fR
.TP 0.2i
\(bu
To export the same file read-write, but make sure
changes are lost after restarting the client or the
server:

\fBnbd-server 2000 /export/nbd/exp-bl-dev
-c\fR
.SH "SEE ALSO"
.PP
nbd-client (8), nbd-server (5), nbd-trdump (8)
.SH "AUTHOR"
.PP
The NBD kernel module and the NBD tools were originally
written by Pavel Machek (pavel@ucw.cz)
.PP
The Linux kernel module is now maintained by Paul Clements
(Paul.Clements@steeleye.com), while the userland tools are
maintained by Wouter Verhelst (<wouter@debian.org>)
.PP
On The Hurd there is a regular translator available to perform the
client side of the protocol, and the use of
\fBnbd-client\fR is not required. Please see the
relevant documentation for more information.
.PP
This manual page was written by Wouter Verhelst (<wouter@debian.org>) 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.