# systemd.dnssd

## 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 /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



           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.
    


## 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



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


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