Provided by: systemd_256.5-2ubuntu3.1_amd64 
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 directories /usr/lib/systemd/dnssd
and /usr/local/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/ or /usr/local/lib. Drop-in files under any of these directories
take precedence over the main network service file wherever located.
[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 │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%a" │ Architecture │ A short string identifying │
│ │ │ the architecture of the │
│ │ │ local system. A string such │
│ │ │ as x86, x86-64 or arm64. See │
│ │ │ the architectures defined │
│ │ │ for ConditionArchitecture= │
│ │ │ in systemd.unit(5) for a │
│ │ │ full list. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%A" │ Operating system image │ The operating system image │
│ │ version │ version identifier of the │
│ │ │ running system, as read from │
│ │ │ the IMAGE_VERSION= field of │
│ │ │ /etc/os-release. If not set, │
│ │ │ resolves to an empty string. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the running │
│ │ │ system, formatted as string. │
│ │ │ See random(4) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%B" │ Operating system build ID │ The operating system build │
│ │ │ identifier of the running │
│ │ │ system, as read from the │
│ │ │ BUILD_ID= field of │
│ │ │ /etc/os-release. If not set, │
│ │ │ resolves to an empty string. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%H" │ Host name │ The hostname of the running │
│ │ │ system. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, formatted as │
│ │ │ string. See machine-id(5) │
│ │ │ for more information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%M" │ Operating system image │ The operating system image │
│ │ identifier │ identifier of the running │
│ │ │ system, as read from the │
│ │ │ IMAGE_ID= field of │
│ │ │ /etc/os-release. If not set, │
│ │ │ resolves to an empty string. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%o" │ Operating system ID │ The operating system │
│ │ │ identifier of the running │
│ │ │ system, as read from the ID= │
│ │ │ field of /etc/os-release. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%w" │ Operating system version ID │ The operating system version │
│ │ │ identifier of the running │
│ │ │ system, as read from the │
│ │ │ VERSION_ID= field of │
│ │ │ /etc/os-release. If not set, │
│ │ │ resolves to an empty string. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%W" │ Operating system variant ID │ The operating system variant │
│ │ │ identifier of the running │
│ │ │ system, as read from the │
│ │ │ VARIANT_ID= field of │
│ │ │ /etc/os-release. If not set, │
│ │ │ resolves to an empty string. │
│ │ │ See os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────────────┼──────────────────────────────┤
│"%%" │ Single percent sign │ Use "%%" in place of "%" to │
│ │ │ specify a single percent │
│ │ │ sign. │
└──────────┴─────────────────────────────┴──────────────────────────────┘
Added in version 236.
Type=
A type of the network service as defined in the section 4.1.2 of RFC 6763[1], e.g. "_http._tcp".
Added in version 236.
SubType=
A subtype of the network service as defined in the section 7.1 of RFC 6763[1], e.g. "_printer".
Added in version 256.
Port=
An IP port number of the network service.
Added in version 236.
Priority=
A priority number set in SRV resource records corresponding to the network service.
Added in version 236.
Weight=
A weight number set in SRV resource records corresponding to the network service.
Added in version 236.
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.
Added in version 236.
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.
Added in version 236.
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