Ubuntu Manpage: systemd.dnssd - DNS-SD configuration

Provided by: systemd_245.4-4ubuntu3.24_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 │
├──────────┼────────────────┼──────────────────────────┤
│"%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, │
│ │ │ formatted as string. See │
│ │ │ machine-id(5) for more │
│ │ │ information. │
├──────────┼────────────────┼──────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the │
│ │ │ running system, │
│ │ │ formatted as string. See │
│ │ │ random(4) for more │
│ │ │ information. │
├──────────┼────────────────┼──────────────────────────┤
│"%H" │ Host name │ The hostname of the │
│ │ │ running system. │
├──────────┼────────────────┼──────────────────────────┤
│"%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
└──────────┴────────────────┴──────────────────────────┘

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"]

NOTES