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
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 │ The operating system │
│ │ image 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 │ The operating system │
│ │ build 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 │ The operating system │
│ │ image 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 │ The operating system │
│ │ version 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 │ The operating system │
│ │ variant 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
systemd 252 SYSTEMD.DNSSD(5)
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