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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             |
           +----------+----------------+---------------------+
           |"%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"]

SEE ALSO
       systemd(1), systemd-resolved.service(8), resolvectl(1)

NOTES
        1. RFC 6763
           https://tools.ietf.org/html/rfc6763

systemd 245                                                   SYSTEMD.DNSSD(5)

NAME | SYNOPSIS | DESCRIPTION | [SERVICE] SECTION OPTIONS | EXAMPLES | SEE ALSO | NOTES