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 turn
38 take precedence over those in /usr/lib or /usr/local/lib. Drop-in files
39 under any of these directories take precedence over the main network
40 service file wherever located.
41
43 The network service file contains a "[Service]" section, which
44 specifies a discoverable network service announced in a local network
45 with 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 │"%m" │ Machine ID │ The machine ID of │
59 │ │ │ the running system, │
60 │ │ │ formatted as │
61 │ │ │ string. See │
62 │ │ │ machine-id(5) for │
63 │ │ │ more information. │
64 ├──────────┼────────────────┼─────────────────────┤
65 │"%b" │ Boot ID │ The boot ID of the │
66 │ │ │ running system, │
67 │ │ │ formatted as │
68 │ │ │ string. See │
69 │ │ │ random(4) for more │
70 │ │ │ information. │
71 ├──────────┼────────────────┼─────────────────────┤
72 │"%H" │ Host name │ The hostname of the │
73 │ │ │ running system. │
74 ├──────────┼────────────────┼─────────────────────┤
75 │"%v" │ Kernel release │ Identical to uname │
76 │ │ │ -r output. │
77 └──────────┴────────────────┴─────────────────────┘
78 Type=
80 A type of the network service as defined in the section 4.1.2 of
81 RFC 6763[1], e.g. "_http._tcp".
82 Port=
84 An IP port number of the network service.
85 Priority=
87 A priority number set in SRV resource records corresponding to the
88 network service.
89 Weight=
91 A weight number set in SRV resource records corresponding to the
92 network service.
93 TxtText=
95 A whitespace-separated list of arbitrary key/value pairs conveying
96 additional information about the named service in the corresponding
97 TXT resource record, e.g. "path=/portal/index.html". Keys and
98 values can contain C-style escape sequences which get translated
99 upon reading configuration files.
100 This option together with TxtData= may be specified more than once,
102 in which case multiple TXT resource records will be created for the
103 service. If the empty string is assigned to this option, the list
104 is reset and all prior assignments will have no effect.
105 TxtData=
107 A whitespace-separated list of arbitrary key/value pairs conveying
108 additional information about the named service in the corresponding
109 TXT resource record where values are base64-encoded string
110 representing any binary data, e.g.
111 "data=YW55IGJpbmFyeSBkYXRhCg==". Keys can contain C-style escape
112 sequences which get translated upon reading configuration files.
113 This option together with TxtText= may be specified more than once,
115 in which case multiple TXT resource records will be created for the
116 service. If the empty string is assigned to this option, the list
117 is reset and all prior assignments will have no effect.
118
120 Example 1. HTTP service
121 # /etc/systemd/dnssd/http.dnssd
123 [Service]
124 Name=%H
125 Type=_http._tcp
126 Port=80
127 TxtText=path=/stats/index.html t=temperature_sensor
128 This makes the http server running on the host discoverable in the
130 local network given MulticastDNS is enabled on the network interface.
131 Now the utility "resolvectl" should be able to resolve the service to
133 the host's name:
134 $ resolvectl service meteo._http._tcp.local
136 meteo._http._tcp.local: meteo.local:80 [priority=0, weight=0]
137 169.254.208.106%senp0s21f0u2u4
138 fe80::213:3bff:fe49:8aa%senp0s21f0u2u4
139 path=/stats/index.html
140 t=temperature_sensor
141 (meteo/_http._tcp/local)
142 -- Information acquired via protocol mDNS/IPv6 in 4.0ms.
144 -- Data is authenticated: yes
145 "Avahi" running on a different host in the same local network should
147 see the service as well:
148 $ avahi-browse -a -r
150 + enp3s0 IPv6 meteo Web Site local
151 + enp3s0 IPv4 meteo Web Site local
152 = enp3s0 IPv6 meteo Web Site local
153 hostname = [meteo.local]
154 address = [fe80::213:3bff:fe49:8aa]
155 port = [80]
156 txt = ["path=/stats/index.html" "t=temperature_sensor"]
157 = enp3s0 IPv4 meteo Web Site local
158 hostname = [meteo.local]
159 address = [169.254.208.106]
160 port = [80]
161 txt = ["path=/stats/index.html" "t=temperature_sensor"]
162
164 systemd(1), systemd-resolved.service(8), resolvectl(1)
165
167 1. RFC 6763
168 https://tools.ietf.org/html/rfc6763
169systemd 243 SYSTEMD.DNSSD(5)