Provided by: systemd_239-7ubuntu10_amd64 bug

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 directory
       /usr/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 /lib. Drop-in
       files under any of these directories take precedence over the main network service file
       wherever located. (Of course, since /run is temporary and /usr/lib is for vendors, it is
       unlikely drop-ins should be used in either of those places.)

[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
           ┌──────────┬────────────────┬──────────────────────────┐
           │SpecifierMeaningDetails                  │
           ├──────────┼────────────────┼──────────────────────────┤
           │"%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