systemd.dnssd(5) — Linux manual page

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

SYSTEMD.DNSSD(5)              systemd.dnssd             SYSTEMD.DNSSD(5)

NAME         top

       systemd.dnssd - DNS-SD configuration

SYNOPSIS         top

       network_service.dnssd

DESCRIPTION         top

       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.

[SERVICE] SECTION OPTIONS         top

       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.   │
           └──────────┴──────────────────┴────────────────────────┘

       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         top

       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         top

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

NOTES         top

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

COLOPHON         top

       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 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  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 249                                             SYSTEMD.DNSSD(5)

Pages that refer to this page: resolvectl(1)