Provided by: systemd_251.4-1ubuntu7_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 /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 │
│ │ version │ image 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 │ The operating system │
│ │ ID │ 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 │
│ │ identifier │ image 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 │ The operating system │
│ │ ID │ 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 │ The operating system │
│ │ ID │ 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. │
└──────────┴──────────────────────────┴──────────────────────────┘
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