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 directories /usr/lib/systemd/dnssd and /usr/local/lib/systemd/dnssd,
19 the volatile runtime network directory /run/systemd/dnssd and the local
20 administration network directory /etc/systemd/dnssd. All configuration
21 files are collectively sorted and processed in lexical order,
22 regardless of the directories in which they live. However, files with
23 identical filenames replace each other. Files in /etc/ have the highest
24 priority, files in /run/ take precedence over files with the same name
25 in /usr/lib/. This can be used to override a system-supplied
26 configuration file with a local file if 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
38 turn take precedence over those in /usr/lib/ or /usr/local/lib. Drop-in
39 files under any of these directories take precedence over the main
40 network service file wherever located.
41
43 The network service file contains a [Service] section, which specifies
44 a discoverable network service announced in a local network with
45 Multicast DNS broadcasts.
46 Name=
48 An instance name of the network service as defined in the section
49 4.1.1 of RFC 6763[1], e.g. "webserver".
50 The option supports simple specifier expansion. The following
52 expansions are understood:
53 Table 1. Specifiers available
55 ┌──────────┬─────────────────────┬────────────────────────┐
56 │Specifier │ Meaning │ Details │
57 ├──────────┼─────────────────────┼────────────────────────┤
58 │"%a" │ Architecture │ A short string │
59 │ │ │ identifying the │
60 │ │ │ architecture of the │
61 │ │ │ local system. A │
62 │ │ │ string such as x86, │
63 │ │ │ x86-64 or arm64. │
64 │ │ │ See the │
65 │ │ │ architectures │
66 │ │ │ defined for │
67 │ │ │ ConditionArchitecture= │
68 │ │ │ in systemd.unit(5) │
69 │ │ │ for a full list. │
70 ├──────────┼─────────────────────┼────────────────────────┤
71 │"%b" │ Boot ID │ The boot ID of the │
72 │ │ │ running system, │
73 │ │ │ formatted as string. │
74 │ │ │ See random(4) for more │
75 │ │ │ information. │
76 ├──────────┼─────────────────────┼────────────────────────┤
77 │"%B" │ Operating system │ The operating system │
78 │ │ build ID │ build identifier of │
79 │ │ │ the running system, as │
80 │ │ │ read from the │
81 │ │ │ BUILD_ID= field of │
82 │ │ │ /etc/os-release. If │
83 │ │ │ not set, resolves to │
84 │ │ │ an empty string. See │
85 │ │ │ os-release(5) for more │
86 │ │ │ information. │
87 ├──────────┼─────────────────────┼────────────────────────┤
88 │"%H" │ Host name │ The hostname of the │
89 │ │ │ running system. │
90 ├──────────┼─────────────────────┼────────────────────────┤
91 │"%m" │ Machine ID │ The machine ID of the │
92 │ │ │ running system, │
93 │ │ │ formatted as string. │
94 │ │ │ See machine-id(5) for │
95 │ │ │ more information. │
96 ├──────────┼─────────────────────┼────────────────────────┤
97 │"%o" │ Operating system ID │ The operating system │
98 │ │ │ identifier of the │
99 │ │ │ running system, as │
100 │ │ │ read from the ID= │
101 │ │ │ field of │
102 │ │ │ /etc/os-release. See │
103 │ │ │ os-release(5) for more │
104 │ │ │ information. │
105 ├──────────┼─────────────────────┼────────────────────────┤
106 │"%v" │ Kernel release │ Identical to uname -r │
107 │ │ │ output. │
108 ├──────────┼─────────────────────┼────────────────────────┤
109 │"%w" │ Operating system │ The operating system │
110 │ │ version ID │ version identifier of │
111 │ │ │ the running system, as │
112 │ │ │ read from the │
113 │ │ │ VERSION_ID= field of │
114 │ │ │ /etc/os-release. If │
115 │ │ │ not set, resolves to │
116 │ │ │ an empty string. See │
117 │ │ │ os-release(5) for more │
118 │ │ │ information. │
119 ├──────────┼─────────────────────┼────────────────────────┤
120 │"%W" │ Operating system │ The operating system │
121 │ │ variant ID │ variant identifier of │
122 │ │ │ the running system, as │
123 │ │ │ read from the │
124 │ │ │ VARIANT_ID= field of │
125 │ │ │ /etc/os-release. If │
126 │ │ │ not set, resolves to │
127 │ │ │ an empty string. See │
128 │ │ │ os-release(5) for more │
129 │ │ │ information. │
130 ├──────────┼─────────────────────┼────────────────────────┤
131 │"%%" │ Single percent sign │ Use "%%" in place of │
132 │ │ │ "%" to specify a │
133 │ │ │ single percent sign. │
134 └──────────┴─────────────────────┴────────────────────────┘
135 Type=
137 A type of the network service as defined in the section 4.1.2 of
138 RFC 6763[1], e.g. "_http._tcp".
139 Port=
141 An IP port number of the network service.
142 Priority=
144 A priority number set in SRV resource records corresponding to the
145 network service.
146 Weight=
148 A weight number set in SRV resource records corresponding to the
149 network service.
150 TxtText=
152 A whitespace-separated list of arbitrary key/value pairs conveying
153 additional information about the named service in the corresponding
154 TXT resource record, e.g. "path=/portal/index.html". Keys and
155 values can contain C-style escape sequences which get translated
156 upon reading configuration files.
157 This option together with TxtData= may be specified more than once,
159 in which case multiple TXT resource records will be created for the
160 service. If the empty string is assigned to this option, the list
161 is reset and all prior assignments will have no effect.
162 TxtData=
164 A whitespace-separated list of arbitrary key/value pairs conveying
165 additional information about the named service in the corresponding
166 TXT resource record where values are base64-encoded string
167 representing any binary data, e.g.
168 "data=YW55IGJpbmFyeSBkYXRhCg==". Keys can contain C-style escape
169 sequences which get translated upon reading configuration files.
170 This option together with TxtText= may be specified more than once,
172 in which case multiple TXT resource records will be created for the
173 service. If the empty string is assigned to this option, the list
174 is reset and all prior assignments will have no effect.
175
177 Example 1. HTTP service
178 # /etc/systemd/dnssd/http.dnssd
180 [Service]
181 Name=%H
182 Type=_http._tcp
183 Port=80
184 TxtText=path=/stats/index.html t=temperature_sensor
185 This makes the http server running on the host discoverable in the
187 local network given MulticastDNS is enabled on the network interface.
188 Now the utility "resolvectl" should be able to resolve the service to
190 the host's name:
191 $ resolvectl service meteo._http._tcp.local
193 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
194 169.254.208.106%senp0s21f0u2u4
195 fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
196 path=/stats/index.html
197 t=temperature_sensor
198 (meteo/_http._tcp/local)
199 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
201 -- Data is authenticated: yes
202 "Avahi" running on a different host in the same local network should
204 see the service as well:
205 $ avahi-browse -a -r
207 + enp3s0 IPv6 meteo Web Site local
208 + enp3s0 IPv4 meteo Web Site local
209 = enp3s0 IPv6 meteo Web Site local
210 hostname = [meteo.local]
211 address = [fe80::213:3bff:fe49:8aa]
212 port = [80]
213 txt = ["path=/stats/index.html" "t=temperature_sensor"]
214 = enp3s0 IPv4 meteo Web Site local
215 hostname = [meteo.local]
216 address = [169.254.208.106]
217 port = [80]
218 txt = ["path=/stats/index.html" "t=temperature_sensor"]
219
221 systemd(1), systemd-resolved.service(8), resolvectl(1)
222
224 1. RFC 6763
225 https://tools.ietf.org/html/rfc6763
226systemd 248 SYSTEMD.DNSSD(5)