'\" t
.TH "SYSTEMD\&.DNSSD" "5" "" "systemd 241" "systemd.dnssd"
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.SH "NAME"
systemd.dnssd \- DNS\-SD configuration
.SH "SYNOPSIS"
.PP
\fInetwork_service\fR\&.dnssd
.SH "DESCRIPTION"
.PP
DNS\-SD setup is performed by
\fBsystemd-resolved\fR(8)\&.
.PP
The main network service file must have the extension
\&.dnssd; other extensions are ignored\&.
.PP
The
\&.dnssd
files are read from the files located in the system network directory
/usr/lib/systemd/dnssd, the volatile runtime network directory
/run/systemd/dnssd
and the local administration network directory
/etc/systemd/dnssd\&. All configuration files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
/etc
have the highest priority, files in
/run
take precedence over files with the same name in
/lib\&. This can be used to override a system\-supplied configuration file with a local file if needed\&.
.PP
Along with the network service file
foo\&.dnssd, a "drop\-in" directory
foo\&.dnssd\&.d/
may exist\&. All files with the suffix
"\&.conf"
from this directory will be parsed after the file itself is parsed\&. This is useful to alter or add configuration settings, without having to modify the main configuration file\&. Each drop\-in file must have appropriate section headers\&.
.PP
In addition to
/etc/systemd/dnssd, drop\-in
"\&.d"
directories can be placed in
/usr/lib/systemd/dnssd
or
/run/systemd/dnssd
directories\&. Drop\-in files in
/etc
take precedence over those in
/run
which in turn take precedence over those in
/lib\&. Drop\-in files under any of these directories take precedence over the main network service file wherever located\&. (Of course, since
/run
is temporary and
/usr/lib
is for vendors, it is unlikely drop\-ins should be used in either of those places\&.)
.SH "[SERVICE] SECTION OPTIONS"
.PP
The network service file contains a
"[Service]"
section, which specifies a discoverable network service announced in a local network with Multicast DNS broadcasts\&.
.PP
\fIName=\fR
.RS 4
An instance name of the network service as defined in the section 4\&.1\&.1 of
\m[blue]\fBRFC 6763\fR\m[]\&\s-2\u[1]\d\s+2, e\&.g\&.
"webserver"\&.
.sp
The option supports simple specifier expansion\&. The following expansions are understood:
.sp
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.B Table\ \&1.\ \&Specifiers available
.TS
allbox tab(:);
lB lB lB.
T{
Specifier
T}:T{
Meaning
T}:T{
Details
T}
.T&
l l l
l l l
l l l
l l l.
T{
"%m"
T}:T{
Machine ID
T}:T{
The machine ID of the running system, formatted as string\&. See \fBmachine-id\fR(5) for more information\&.
T}
T{
"%b"
T}:T{
Boot ID
T}:T{
The boot ID of the running system, formatted as string\&. See \fBrandom\fR(4) for more information\&.
T}
T{
"%H"
T}:T{
Host name
T}:T{
The hostname of the running system\&.
T}
T{
"%v"
T}:T{
Kernel release
T}:T{
Identical to \fBuname \-r\fR output\&.
T}
.TE
.sp 1
.RE
.PP
\fIType=\fR
.RS 4
A type of the network service as defined in the section 4\&.1\&.2 of
\m[blue]\fBRFC 6763\fR\m[]\&\s-2\u[1]\d\s+2, e\&.g\&.
"_http\&._tcp"\&.
.RE
.PP
\fIPort=\fR
.RS 4
An IP port number of the network service\&.
.RE
.PP
\fIPriority=\fR
.RS 4
A priority number set in SRV resource records corresponding to the network service\&.
.RE
.PP
\fIWeight=\fR
.RS 4
A weight number set in SRV resource records corresponding to the network service\&.
.RE
.PP
\fITxtText=\fR
.RS 4
A whitespace\-separated list of arbitrary key/value pairs conveying additional information about the named service in the corresponding TXT resource record, e\&.g\&.
"path=/portal/index\&.html"\&. Keys and values can contain C\-style escape sequences which get translated upon reading configuration files\&.
.sp
This option together with
\fITxtData=\fR
may be specified more than once, in which case multiple TXT resource records will be created for the service\&. If the empty string is assigned to this option, the list is reset and all prior assignments will have no effect\&.
.RE
.PP
\fITxtData=\fR
.RS 4
A whitespace\-separated list of arbitrary key/value pairs conveying additional information about the named service in the corresponding TXT resource record where values are base64\-encoded string representing any binary data, e\&.g\&.
"data=YW55IGJpbmFyeSBkYXRhCg=="\&. Keys can contain C\-style escape sequences which get translated upon reading configuration files\&.
.sp
This option together with
\fITxtText=\fR
may be specified more than once, in which case multiple TXT resource records will be created for the service\&. If the empty string is assigned to this option, the list is reset and all prior assignments will have no effect\&.
.RE
.SH "EXAMPLES"
.PP
\fBExample\ \&1.\ \&HTTP service\fR
.sp
.if n \{\
.RS 4
.\}
.nf
# /etc/systemd/dnssd/http\&.dnssd
[Service]
Name=%H
Type=_http\&._tcp
Port=80
TxtText=path=/stats/index\&.html t=temperature_sensor
.fi
.if n \{\
.RE
.\}
.PP
This makes the http server running on the host discoverable in the local network given MulticastDNS is enabled on the network interface\&.
.PP
Now the utility
"resolvectl"
should be able to resolve the service to the host\*(Aqs name:
.sp
.if n \{\
.RS 4
.\}
.nf
$ resolvectl service meteo\&._http\&._tcp\&.local
meteo\&._http\&._tcp\&.local: meteo\&.local:80 [priority=0, weight=0]
                        169\&.254\&.208\&.106%senp0s21f0u2u4
                        fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
                        path=/stats/index\&.html
                        t=temperature_sensor
                        (meteo/_http\&._tcp/local)

\-\- Information acquired via protocol mDNS/IPv6 in 4\&.0ms\&.
\-\- Data is authenticated: yes
.fi
.if n \{\
.RE
.\}
.PP
"Avahi"
running on a different host in the same local network should see the service as well:
.sp
.if n \{\
.RS 4
.\}
.nf
$ avahi\-browse \-a \-r
+ enp3s0 IPv6 meteo                                         Web Site             local
+ enp3s0 IPv4 meteo                                         Web Site             local
= enp3s0 IPv6 meteo                                         Web Site             local
   hostname = [meteo\&.local]
   address = [fe80::213:3bff:fe49:8aa]
   port = [80]
   txt = ["path=/stats/index\&.html" "t=temperature_sensor"]
= enp3s0 IPv4 meteo                                         Web Site             local
   hostname = [meteo\&.local]
   address = [169\&.254\&.208\&.106]
   port = [80]
   txt = ["path=/stats/index\&.html" "t=temperature_sensor"]
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBsystemd-resolved.service\fR(8),
\fBresolvectl\fR(1)
.SH "NOTES"
.IP " 1." 4
RFC 6763
.RS 4
\%https://tools.ietf.org/html/rfc6763
.RE