1SYSTEMD.DNSSD(5) systemd.dnssd SYSTEMD.DNSSD(5)
2
6 systemd.dnssd - DNS-SD configuration
7
9 network_service.dnssd
10
12 DNS-SD setup is performed by systemd-resolved(8).
13 The main network service file must have the extension .dnssd; other
15 extensions are ignored.
16 The .dnssd files are read from the files located in the system network
18 directory /usr/lib/systemd/dnssd, the volatile runtime network
19 directory /run/systemd/dnssd and the local administration network
20 directory /etc/systemd/dnssd. All configuration files are collectively
21 sorted and processed in lexical order, regardless of the directories in
22 which they live. However, files with identical filenames replace each
23 other. Files in /etc have the highest priority, files in /run take
24 precedence over files with the same name in /usr/lib. This can be used
25 to override a system-supplied configuration file with a local file if
26 needed.
27 Along with the network service file foo.dnssd, a "drop-in" directory
29 foo.dnssd.d/ may exist. All files with the suffix ".conf" from this
30 directory will be parsed after the file itself is parsed. This is
31 useful to alter or add configuration settings, without having to modify
32 the main configuration file. Each drop-in file must have appropriate
33 section headers.
34 In addition to /etc/systemd/dnssd, drop-in ".d" directories can be
36 placed in /usr/lib/systemd/dnssd or /run/systemd/dnssd directories.
37 Drop-in files in /etc take precedence over those in /run which in turn
38 take precedence over those in /usr/lib. Drop-in files under any of
39 these directories take precedence over the main network service file
40 wherever located. (Of course, since /run is temporary and /usr/lib is
41 for vendors, it is unlikely drop-ins should be used in either of those
42 places.)
43
45 The network service file contains a "[Service]" section, which
46 specifies a discoverable network service announced in a local network
47 with Multicast DNS broadcasts.
48 Name=
50 An instance name of the network service as defined in the section
51 4.1.1 of RFC 6763[1], e.g. "webserver".
52 The option supports simple specifier expansion. The following
54 expansions are understood:
55 Table 1. Specifiers available
57 ┌──────────┬────────────────┬─────────────────────┐
58 │Specifier │ Meaning │ Details │
59 ├──────────┼────────────────┼─────────────────────┤
60 │"%m" │ Machine ID │ The machine ID of │
61 │ │ │ the running system, │
62 │ │ │ formatted as │
63 │ │ │ string. See │
64 │ │ │ machine-id(5) for │
65 │ │ │ more information. │
66 ├──────────┼────────────────┼─────────────────────┤
67 │"%b" │ Boot ID │ The boot ID of the │
68 │ │ │ running system, │
69 │ │ │ formatted as │
70 │ │ │ string. See │
71 │ │ │ random(4) for more │
72 │ │ │ information. │
73 ├──────────┼────────────────┼─────────────────────┤
74 │"%H" │ Host name │ The hostname of the │
75 │ │ │ running system. │
76 ├──────────┼────────────────┼─────────────────────┤
77 │"%v" │ Kernel release │ Identical to uname │
78 │ │ │ -r output. │
79 └──────────┴────────────────┴─────────────────────┘
80 Type=
82 A type of the network service as defined in the section 4.1.2 of
83 RFC 6763[1], e.g. "_http._tcp".
84 Port=
86 An IP port number of the network service.
87 Priority=
89 A priority number set in SRV resource records corresponding to the
90 network service.
91 Weight=
93 A weight number set in SRV resource records corresponding to the
94 network service.
95 TxtText=
97 A whitespace-separated list of arbitrary key/value pairs conveying
98 additional information about the named service in the corresponding
99 TXT resource record, e.g. "path=/portal/index.html". Keys and
100 values can contain C-style escape sequences which get translated
101 upon reading configuration files.
102 This option together with TxtData= may be specified more than once,
104 in which case multiple TXT resource records will be created for the
105 service. If the empty string is assigned to this option, the list
106 is reset and all prior assignments will have no effect.
107 TxtData=
109 A whitespace-separated list of arbitrary key/value pairs conveying
110 additional information about the named service in the corresponding
111 TXT resource record where values are base64-encoded string
112 representing any binary data, e.g.
113 "data=YW55IGJpbmFyeSBkYXRhCg==". Keys can contain C-style escape
114 sequences which get translated upon reading configuration files.
115 This option together with TxtText= may be specified more than once,
117 in which case multiple TXT resource records will be created for the
118 service. If the empty string is assigned to this option, the list
119 is reset and all prior assignments will have no effect.
120
122 Example 1. HTTP service
123 # /etc/systemd/dnssd/http.dnssd
125 [Service]
126 Name=%H
127 Type=_http._tcp
128 Port=80
129 TxtText=path=/stats/index.html t=temperature_sensor
130 This makes the http server running on the host discoverable in the
132 local network given MulticastDNS is enabled on the network interface.
133 Now the utility "resolvectl" should be able to resolve the service to
135 the host's name:
136 $ resolvectl service meteo._http._tcp.local
138 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
139 169.254.208.106%senp0s21f0u2u4
140 fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
141 path=/stats/index.html
142 t=temperature_sensor
143 (meteo/_http._tcp/local)
144 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
146 -- Data is authenticated: yes
147 "Avahi" running on a different host in the same local network should
149 see the service as well:
150 $ avahi-browse -a -r
152 + enp3s0 IPv6 meteo Web Site local
153 + enp3s0 IPv4 meteo Web Site local
154 = enp3s0 IPv6 meteo Web Site local
155 hostname = [meteo.local]
156 address = [fe80::213:3bff:fe49:8aa]
157 port = [80]
158 txt = ["path=/stats/index.html" "t=temperature_sensor"]
159 = enp3s0 IPv4 meteo Web Site local
160 hostname = [meteo.local]
161 address = [169.254.208.106]
162 port = [80]
163 txt = ["path=/stats/index.html" "t=temperature_sensor"]
164
166 systemd(1), systemd-resolved.service(8), resolvectl(1)
167
169 1. RFC 6763
170 https://tools.ietf.org/html/rfc6763
171systemd 239 SYSTEMD.DNSSD(5)