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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | [SERVICE] SECTION OPTIONS | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
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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. │
├───────────┼──────────────────┼────────────────────────┤
│ "%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 │ The operating system │
│ │ ID │ 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 │ Use "%%" in place of │
│ │ sign │ "%" 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.
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 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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 258~rc2 SYSTEMD.DNSSD(5)
Pages that refer to this page: resolvectl(1), org.freedesktop.resolve1(5), systemd.directives(7), systemd.index(7), systemd-resolved.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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