SYSTEMD.DNSSD(5) systemd.dnssd SYSTEMD.DNSSD(5)
NAME
systemd.dnssd - DNS-SD configuration
SYNOPSIS
network_service.dnssd
DESCRIPTION
DNS-SD setup is performed by systemd-resolved(8).
The main network service file must have the extension .dnssd; other
extensions are ignored.
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 /usr/lib. This can be used
to override a system-supplied configuration file with a local file if
needed.
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.
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 /usr/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.)
[SERVICE] SECTION OPTIONS
The network service file contains a "[Service]" section, which
specifies a discoverable network service announced in a local network
with Multicast DNS broadcasts.
Name=
An instance name of the network service as defined in the section
4.1.1 of RFC 6763[1], e.g. "webserver".
The option supports simple specifier expansion. The following
expansions are understood:
Table 1. Specifiers available
+----------+----------------+---------------------+
|Specifier | Meaning | Details |
+----------+----------------+---------------------+
|"%m" | Machine ID | The machine ID of |
| | | the running system, |
| | | formatted as |
| | | string. See |
| | | machine-id(5) for |
| | | more information. |
+----------+----------------+---------------------+
|"%b" | Boot ID | The boot ID of the |
| | | running system, |
| | | formatted as |
| | | string. See |
| | | random(4) for more |
| | | information. |
+----------+----------------+---------------------+
|"%H" | Host name | The hostname of the |
| | | running system. |
+----------+----------------+---------------------+
|"%v" | Kernel release | Identical to uname |
| | | -r output. |
+----------+----------------+---------------------+
Type=
A type of the network service as defined in the section 4.1.2 of
RFC 6763[1], e.g. "_http._tcp".
Port=
An IP port number of the network service.
Priority=
A priority number set in SRV resource records corresponding to the
network service.
Weight=
A weight number set in SRV resource records corresponding to the
network service.
TxtText=
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.
This option together with TxtData= 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.
TxtData=
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.
This option together with TxtText= 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.
EXAMPLES
Example 1. HTTP service
# /etc/systemd/dnssd/http.dnssd
[Service]
Name=%H
Type=_http._tcp
Port=80
TxtText=path=/stats/index.html t=temperature_sensor
This makes the http server running on the host discoverable in the
local network given MulticastDNS is enabled on the network interface.
Now the utility "resolvectl" should be able to resolve the service to
the host's name:
$ 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
"Avahi" running on a different host in the same local network should
see the service as well:
$ 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"]
SEE ALSO
systemd(1), systemd-resolved.service(8), resolvectl(1)
NOTES
1. RFC 6763
https://tools.ietf.org/html/rfc6763
systemd 239 SYSTEMD.DNSSD(5)
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