1resolv.conf(4) File Formats resolv.conf(4)
2
6 resolv.conf - resolver configuration file
7
9 /etc/resolv.conf
10
13 The resolver is a set of routines that provide access to the Internet
14 Domain Name System. See resolver(3RESOLV). resolv.conf is a configura‐
15 tion file that contains the information that is read by the resolver
16 routines the first time they are invoked by a process. The file is
17 designed to be human readable and contains a list of keywords with val‐
18 ues that provide various types of resolver information.
19 The resolv.conf file contains the following configuration directives:
22 nameserver Specifies the IPv4 or IPv6 Internet address of a
24 name server that the resolver is to query. Up to
25 MAXNS name servers may be listed, one per key‐
26 word. See <resolv.h>. If there are multiple
27 servers, the resolver library queries them in
28 the order listed. If no name server entries are
29 present, the resolver library queries the name
30 server on the local machine. The resolver
31 library follows the algorithm to try a name
32 server until the query times out. It then tries
33 the name servers that follow, until each query
34 times out. It repeats all the name servers until
35 a maximum number of retries are made.
36 domain Specifies the local domain name. Most queries
39 for names within this domain can use short names
40 relative to the local domain. If no domain entry
41 is present, the domain is determined from sys‐
42 info(2) or from gethostname(3C). (Everything
43 after the first `.' is presumed to be the domain
44 name.) If the host name does not contain a
45 domain part, the root domain is assumed. You can
46 use the LOCALDOMAIN environment variable to
47 override the domain name.
48 search The search list for host name lookup. The search
51 list is normally determined from the local
52 domain name. By default, it contains only the
53 local domain name. You can change the default
54 behavior by listing the desired domain search
55 path following the search keyword, with spaces
56 or tabs separating the names. Most resolver
57 queries will be attempted using each component
58 of the search path in turn until a match is
59 found. This process may be slow and will gener‐
60 ate a lot of network traffic if the servers for
61 the listed domains are not local. Queries will
62 time out if no server is available for one of
63 the domains.
64 The search list is currently limited to six
66 domains and a total of 256 characters.
67 sortlistaddresslist Allows addresses returned by the libresolv-
70 internal gethostbyname() to be sorted. A
71 sortlist is specified by IP address netmask
72 pairs. The netmask is optional and defaults to
73 the natural netmask of the net. The IP address
74 and optional network pairs are separated by
75 slashes. Up to 10 pairs may be specified. For
76 example:
77 sortlist 130.155.160.0/255.255.240.0 130.155.0.0
79 options Allows certain internal resolver variables to be
84 modified. The syntax is
85 options option ...
87 where option is one of the following:
90 debug Sets RES_DEBUG in the
92 _res.options field.
93 ndots:n Sets a threshold floor for the
96 number of dots which must
97 appear in a name given to
98 res_query() before an initial
99 absolute (as-is) query is per‐
100 formed. See resolver(3RESOLV).
101 The default value for n is 1,
102 which means that if there are
103 any dots in a name, the name
104 is tried first as an absolute
105 name before any search list
106 elements are appended to it.
107 timeout:n Sets the amount of time the
110 retrans:n resolver will wait for a
111 response from a remote name
112 server before retrying the
113 query by means of a different
114 name server. Measured in sec‐
115 onds, the default is RES_TIME‐
116 OUT. See <resolv.h>. The time‐
117 out and retrans values are the
118 starting point for an exponen‐
119 tial back off procedure where
120 the timeout is doubled for
121 every retransmit attempt.
122 attempts:n Sets the number of times the
125 retry:n resolver will send a query to
126 its name servers before giving
127 up and returning an error to
128 the calling application. The
129 default is RES_DFLRETRY. See
130 <resolv.h>.
131 rotate Sets RES_ROTATE in
134 _res.options. The name servers
135 are queried round-robin from
136 among those listed. The query
137 load is spread among all
138 listed servers, rather than
139 having all clients try the
140 first listed server first
141 every time.
142 no-check-names Sets RES_NOCHECKNAME in
145 _res.options. This disables
146 the modern BIND checking of
147 incoming host names and mail
148 names for invalid characters
149 such as underscore (_), non-
150 ASCII, or control characters.
151 inet6 Sets RES_USE_INET6 in
154 _res.options. In the Solaris
155 BIND port, this has no effect
156 on gethostbyname(3NSL). To
157 retrieve IPv6 addresses or
158 IPv4 addresses, use getad‐
159 drinfo(3SOCKET) instead of
160 setting inet6.
161 The domain and search keywords are mutually exclusive. If more than one
166 instance of these keywords is present, the last instance takes prece‐
167 dence.
168 You can override the search keyword of the system resolv.conf file on a
171 per-process basis by setting the environment variable LOCALDOMAIN to a
172 space-separated list of search domains.
173 You can amend the options keyword of the system resolv.conf file on a
176 per-process basis by setting the environment variable RES_OPTIONS to a
177 space-separated list of resolver options.
178 The keyword and value must appear on a single line. Start the line with
181 the keyword, for example, nameserver, followed by the value, separated
182 by white space.
183
185 /etc/resolv.conf
186
189 See attributes(5) for descriptions of the following attributes:
190 ┌─────────────────────────────┬─────────────────────────────┐
195 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
196 ├─────────────────────────────┼─────────────────────────────┤
197 │Interface Stability │Standard BIND 8.3.3 │
198 └─────────────────────────────┴─────────────────────────────┘
199
201 domainname(1M), sysinfo(2), gethostbyname(3NSL), getnameinfo(3SOCKET),
202 getipnodebyname(3SOCKET), gethostname(3C), resolver(3RESOLV),
203 attributes(5)
204 Vixie, Paul, Dunlap, Keven J., Karels, Michael J. Name Server Opera‐
207 tions Guide for BIND. Internet Software Consortium, 1996.
208SunOS 5.11 15 Dec 2004 resolv.conf(4)