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1 perry 1 RESOLVER
2 !!!RESOLVER
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 FILES
7 SEE ALSO
8 ----
9 !!NAME
10
11
12 resolver - resolver configuration file
13 !!SYNOPSIS
14
15
16 /etc/resolv.conf
17 !!DESCRIPTION
18
19
20 The ''resolver'' is a set of routines in the C library
21 that provide access to the Internet Domain Name System. The
22 resolver configuration file contains information that is
23 read by the resolver routines the first time they are
24 invoked by a process. The file is designed to be human
25 readable and contains a list of keywords with values that
26 provide various types of resolver information.
27
28
29 On a normally configured system this file should not be
30 necessary. The only name server to be queried will be on the
31 local machine, the domain name is determined from the host
32 name, and the domain search path is constructed from the
33 domain name.
34
35
36 The different configuration options are:
37
38
39 __nameserver__
40
41
42 Internet address (in dot notation) of a name server that the
43 resolver should query. Up to MAXNS (currently 3) name
44 servers may be listed, one per keyword. If there are
45 multiple servers, the resolver library queries them in the
46 order listed. If no __nameserver__ entries are present,
47 the default is to use the name server on the local machine.
48 (The algorithm used is to try a name server, and if the
49 query times out, try the next, until out of name servers,
50 then repeat trying all the name servers until a maximum
51 number of retries are made).
52
53
54 __domain__
55
56
57 Local domain name. Most queries for names within this domain
58 can use short names relative to the local domain. If no
59 __domain__ entry is present, the domain is determined
60 from the local host name returned by ''gethostname''();
61 the domain part is taken to be everything after the first
62 `.'. Finally, if the host name does not contain a domain
63 part, the root domain is assumed.
64
65
66 __search__
67
68
69 Search list for host-name lookup. The search list is
70 normally determined from the local domain name; by default,
71 it contains only the local domain name. This may be changed
72 by listing the desired domain search path following the
73 ''search'' keyword with spaces or tabs separating the
74 names. Most resolver queries will be attempted using each
75 component of the search path in turn until a match is found.
76 Note that this process may be slow and will generate a lot
77 of network traffic if the servers for the listed domains are
78 not local, and that queries will time out if no server is
79 available for one of the domains.
80
81
82 The search list is currently limited to six domains with a
83 total of 256 characters.
84
85
86 __sortlist__
87
88
89 Sortlist allows addresses returned by gethostbyname to be
90 sorted. A sortlist is specified by IP address netmask pairs.
91 The netmask is optional and defaults to the natural netmask
92 of the net. The IP address and optional network pairs are
93 separated by slashes. Up to 10 pairs may be
94 specified.
95
96
97 e.g. sortlist 130.155.160.0/255.255.240.0
98 130.155.0.0
99
100
101 __options__
102
103
104 Options allows certain internal resolver variables to be
105 modified. The syntax is
106
107
108 __options__ ''option ...''
109
110
111 where ''option'' is one of the following:
112
113
114 __debug__ -- sets RES_DEBUG in _res.options.
115
116
117 __ndots:__''n'' -- sets a threshold for the number of
118 dots which must appear in a name given to __res_query__
119 (see resolver(3)) before an ''initial absolute
120 query'' will be made. The default for ''n'' is ``1'',
121 meaning that if there are any dots in a name, the name will
122 be tried first as an absolute name before any ''search
123 list'' elements are appended to it.
124
125
126 The ''domain'' and ''search'' keywords are mutually
127 exclusive. If more than one instance of these keywords is
128 present, the last instance wins.
129
130
131 The ''search'' keyword of a system's ''resolv.conf''
132 file can be overridden on a per-process basis by setting the
133 environment variable `` LOCALDOMAIN '' to a
134 space-separated list of search domains.
135
136
137 The ''options'' keyword of a system's ''resolv.conf''
138 file can be amended on a per-process basis by setting the
139 environment variable `` RES_OPTIONS '' to a
140 space-separated list of resolver options as explained above
141 under __options__.
142
143
144 The keyword and value must appear on a single line, and the
145 keyword (e.g. __nameserver__) must start the line. The
146 value follows the keyword, separated by white
147 space.
148 !!FILES
149
150
151 ''/etc/resolv.conf''
152 !!SEE ALSO
153
154
155 gethostbyname(3), hostname(7),
156 named(8),
157 Name Server Operations Guide for BIND
158 ----
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