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NAME | SYNOPSIS | DESCRIPTION | [SERVICE] SECTION OPTIONS | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
SYSTEMD.DNSSD(5) systemd.dnssd SYSTEMD.DNSSD(5)
systemd.dnssd - DNS-SD configuration
network_service.dnssd
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.
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. │
├──────────┼─────────────────────┼────────────────────────┤
│"%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. │
├──────────┼─────────────────────┼────────────────────────┤
│"%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.
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"]
systemd(1), systemd-resolved.service(8), resolvectl(1)
1. RFC 6763
https://tools.ietf.org/html/rfc6763
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 246 SYSTEMD.DNSSD(5)
Pages that refer to this page: resolvconf(1) , resolvectl(1) , 30-systemd-environment-d-generator(7) , systemd.directives(7) , systemd.index(7)