.\" -*- mode: troff; coding: utf-8 -*-
.\" Automatically generated by Podwrapper::Man 1.38.2 (Pod::Simple 3.43)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>.
.ie n \{\
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
.    if \nF \{\
.        de IX
.        tm Index:\\$1\t\\n%\t"\\$2"
..
.        if !\nF==2 \{\
.            nr % 0
.            nr F 2
.        \}
.    \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "nbdkit-service 1"
.TH nbdkit-service 1 2024-05-10 nbdkit-1.38.2 NBDKIT
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
nbdkit\-service \- running nbdkit as a service, and systemd socket activation
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Most people start nbdkit from the command line or run it from another
program (see \fBnbdkit\-captive\fR\|(1).  It is also possible to run nbdkit
as a standalone service, which is what this page describes.
.SH "SOCKET ACTIVATION"
.IX Header "SOCKET ACTIVATION"
nbdkit supports socket activation (sometimes called systemd socket
activation).  This is a simple protocol where instead of nbdkit itself
opening the listening socket(s), the parent process (typically
systemd) passes in pre-opened file descriptors.  Socket activation
lets you serve infrequent NBD requests using a superserver without
needing nbdkit to be running the whole time.
.PP
Socket activation is triggered when both the \f(CW\*(C`LISTEN_FDS\*(C'\fR and
\&\f(CW\*(C`LISTEN_PID\*(C'\fR environment variables are set.  In this mode using
\&\fI\-i\fR, \fI\-p\fR, \fI\-\-run\fR, \fI\-s\fR or \fI\-U\fR flags on the command line is
illegal and will cause an error.  Also in this mode nbdkit does not
fork into the background (ie. \fI\-f\fR is implied).
.SS "Using socket activation with systemd"
.IX Subsection "Using socket activation with systemd"
To use nbdkit with socket activation from systemd, create a unit file
ending in \f(CW\*(C`.socket\*(C'\fR (eg. \fI/etc/systemd/system/nbdkit.socket\fR)
containing:
.PP
.Vb 2
\& [Unit]
\& Description=NBDKit Network Block Device server
\&
\& [Socket]
\& ListenStream=10809
\&
\& [Install]
\& WantedBy=sockets.target
.Ve
.PP
There are various formats for the \f(CW\*(C`ListenStream\*(C'\fR key.  See
\&\fBsystemd.socket\fR\|(5) for more information.
.PP
Also create a service unit (eg. \fI/etc/systemd/system/nbdkit.service\fR)
containing:
.PP
.Vb 2
\& [Service]
\& ExecStart=/usr/sbin/nbdkit file /path/to/serve
.Ve
.PP
For more information on systemd and socket activation, see
http://0pointer.de/blog/projects/socket\-activation.html
.SH "INETD AND XINETD"
.IX Header "INETD AND XINETD"
You can run nbdkit from \fBinetd\fR\|(8) or \fBxinetd\fR\|(8).  For inetd use:
.PP
.Vb 1
\& nbd stream tcp nowait root /usr/sbin/nbdkit nbdkit \-s file /tmp/disk.img
.Ve
.PP
For xinetd create a file \fI/etc/xinetd.d/nbdkit\fR containing:
.PP
.Vb 8
\& service nbd
\& {
\&     socket_type = stream
\&     wait = no
\&     user = root
\&     server = /usr/sbin/nbdkit
\&     server_args = \-s file /tmp/disk.img
\& }
.Ve
.SH LOGGING
.IX Header "LOGGING"
Error messages from nbdkit can be sent to standard error
(\fI\-\-log=stderr\fR), or to the system log (\fI\-\-log=syslog\fR), or can be
discarded completely (\fI\-\-log=null\fR, not recommended for normal use).
.PP
The default, if \fI\-\-log\fR is not specified on the command line, is to
send error messages to stderr, unless nbdkit forks into the background
in which case they are sent to syslog.
.PP
In detail:
.IP "Messages go to standard error (stderr):" 4
.IX Item "Messages go to standard error (stderr):"
When running from the command line in the foreground.
.Sp
When using systemd socket activation.
.Sp
Using \fI\-\-log=stderr\fR forces all messages to go to standard error.
.IP "Messages go to the system log (syslog):" 4
.IX Item "Messages go to the system log (syslog):"
When running from the command line, forked into the background.
.Sp
Using \fI\-\-log=syslog\fR forces all messages to go to the system log.
.PP
Debug messages (\fI\-v\fR/\fI\-\-verbose\fR) always go to standard error and
are never sent to the system log.
.SH AF_VSOCK
.IX Header "AF_VSOCK"
On Linux nbdkit supports the \f(CW\*(C`AF_VSOCK\*(C'\fR address family / protocol.
This allows you to serve NBD devices into virtual machines without
using a regular network connection.
.PP
\&\fBNote\fR that this is different from the usual case where you present
NBD as a virtual block device to a guest (which the guest sees as
something like a SATA or virtio-scsi disk).  With \f(CW\*(C`AF_VSOCK\*(C'\fR the
virtual machine sees a raw NBD socket which it can connect to by
opening an \f(CW\*(C`AF_VSOCK\*(C'\fR connection.  Only libnbd supports \f(CW\*(C`AF_VSOCK\*(C'\fR
NBD client connections at the time of writing (2019).  For more about
this protocol, see https://wiki.qemu.org/Features/VirtioVsock
.SS "AF_VSOCK example"
.IX Subsection "AF_VSOCK example"
To set up an \f(CW\*(C`AF_VSOCK\*(C'\fR server, use for example:
.PP
.Vb 1
\& nbdkit \-\-vsock [\-\-port PORT] memory 1G
.Ve
.PP
The optional \fI\-p\fR/\fI\-\-port\fR argument is used to change the
\&\f(CW\*(C`AF_VSOCK\*(C'\fR port number.  These port numbers exist in a different
namespace from TCP/IP port numbers.  Also unlike TCP, the port numbers
are 32 bit.  The default port is 10809.
.PP
The guest that wishes to access nbdkit must be configured for
virtio-vsock.  On the qemu command line use:
.PP
.Vb 1
\& qemu ... \-device vhost\-vsock\-pci,id=vhost\-vsock\-pci0
.Ve
.PP
For libvirt add this element to the \f(CW\*(C`<devices>\*(C'\fR section:
.PP
.Vb 1
\& <vsock/>
.Ve
.PP
If you see the error \f(CW\*(C`unable to open vhost\-vsock device\*(C'\fR then you may
have to unload the VMCI transport on the host:
.PP
.Vb 1
\& modprobe \-r vmw_vsock_vmci_transport
.Ve
.PP
Once nbdkit and the guest are running, from inside the guest you can
connect to nbdkit on the host using libnbd:
.PP
.Vb 1
\& nbdsh \-c \*(Aqh.connect_vsock(2, 10809)\*(Aq \-c \*(Aqprint(h.get_size())\*(Aq
.Ve
.SH "ENVIRONMENT VARIABLES"
.IX Header "ENVIRONMENT VARIABLES"
.ie n .IP """LISTEN_FDS""" 4
.el .IP \f(CWLISTEN_FDS\fR 4
.IX Item "LISTEN_FDS"
.PD 0
.ie n .IP """LISTEN_PID""" 4
.el .IP \f(CWLISTEN_PID\fR 4
.IX Item "LISTEN_PID"
.PD
If present in the environment when nbdkit starts up, these trigger
"SOCKET ACTIVATION".
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-client\fR\|(1),
\&\fBnbdkit\-exitlast\-filter\fR\|(1),
\&\fBnbdkit\-exitwhen\-filter\fR\|(1),
\&\fBnbdkit\-ip\-filter\fR\|(1),
\&\fBnbdkit\-limit\-filter\fR\|(1),
\&\fBsystemd\fR\|(1),
\&\fBsystemd.socket\fR\|(5),
\&\fBinetd\fR\|(8),
\&\fBxinetd\fR\|(8),
\&\fBsyslog\fR\|(3),
\&\fBrsyslogd\fR\|(8),
\&\fBjournalctl\fR\|(1),
\&\fBnbdsh\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.PP
Pino Toscano
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
.IP \(bu 4
Neither the name of Red Hat nor the names of its contributors may be
used to endorse or promote products derived from this software without
specific prior written permission.
.PP
THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.