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.TH "NBD-SERVER" "1" "07 juni 2006" "" ""

.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\fIport\fB\fR \fB\fIfilename\fB\fR [ \fB\fIsize\fB\fR ] [ \fB-r\fR ] [ \fB-m\fR ] [ \fB-c\fR ] [ \fB-a \fItimeout\fB\fR ] [ \fB-l \fIhost list\fB\fR ]

.SH "DESCRIPTION"
.PP
This manual page documents the
\fBnbd-server\fR command.
.PP
This manual page was written for the Debian GNU/Linux distribution
because the original program does not have a manual page.
.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 "nbd_server.allow" in the current directory (by default; a different file can be chosen with the '-l' option).
This file must list the IP-addresses 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.
.SH "OPTIONS"
.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 usefull 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.

The files must all be 1GB in size.

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
\fBtimeout\fR
Maximum number of idle seconds. If a connection is
inactive for this amount of time, it is terminated; this is to
avoid stale nbd-server processes staying in memory. Use of
this option is strongly recommended.
.TP
\fBhost list\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.
.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), http://nbd.sourceforge.net/roadmap.html
.SH "AUTHOR"
.PP
The NBD kernel module and the NBD tools were originally
written by Pavel Machek (pavel@ucw.cz)
.PP
The 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
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.