resolver.cat5 revision 1.1.1.1.6.2
1RESOLVER(5) BSD File Formats Manual RESOLVER(5) 2 3NNAAMMEE 4 rreessoollvveerr - resolver configuration file 5 6SSYYNNOOPPSSIISS 7 _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f 8 9DDEESSCCRRIIPPTTIIOONN 10 The rreessoollvveerr is a set of routines in the C library (resolve(3)) that pro��� 11 vide access to the Internet Domain Name System. The rreessoollvveerr configura��� 12 tion file contains information that is read by the rreessoollvveerr routines the 13 first time they are invoked by a process. The file is designed to be 14 human readable and contains a list of keywords with values that provide 15 various types of rreessoollvveerr information. 16 17 On a normally configured system, this file should not be necessary. The 18 only name server to be queried will be on the local machine, the domain 19 name is determined from the host name, and the domain search path is con��� 20 structed from the domain name. 21 22 The different configuration directives are: 23 24 nameserver 25 Internet address (in dot notation) of a name server that the 26 rreessoollvveerr should query. Up to MAXNS (see _<_r_e_s_o_l_v_._h_>) name 27 servers may be listed, one per keyword. If there are multiple 28 servers, the rreessoollvveerr library queries them in the order listed. 29 If no nameserver entries are present, the default is to use the 30 name server on the local machine. (The algorithm used is to try 31 a name server, and if the query times out, try the next, until 32 out of name servers, then repeat trying all the name servers 33 until a maximum number of retries are made). 34 35 domain Local domain name. Most queries for names within this domain 36 can use short names relative to the local domain. If no domain 37 entry is present, the domain is determined from the local host 38 name returned by gethostname; the domain part is taken to be 39 everything after the first ���.���. Finally, if the host name does 40 not contain a domain part, the root domain is assumed. 41 42 search Search list for host-name lookup. The search list is normally 43 determined from the local domain name; by default, it contains 44 only the local domain name. This may be changed by listing the 45 desired domain search path following the search keyword with 46 spaces or tabs separating the names. Most rreessoollvveerr queries will 47 be attempted using each component of the search path in turn 48 until a match is found. Note that this process may be slow and 49 will generate a lot of network traffic if the servers for the 50 listed domains are not local, and that queries will time out if 51 no server is available for one of the domains. 52 53 The search list is currently limited to six domains with a total 54 of 256 characters. 55 56 sortlist 57 Allows addresses returned by gethostbyname to be sorted. A 58 sortlist is specified by IP address netmask pairs. The netmask 59 is optional and defaults to the natural netmask of the net. The 60 IP address and optional network pairs are separated by slashes. 61 Up to 10 pairs may be specified. For example: 62 63 sortlist 130.155.160.0/255.255.240.0 130.155.0.0 64 65 options Allows certain internal rreessoollvveerr variables to be modified. The 66 syntax is 67 options _o_p_t_i_o_n _._._. 68 where _o_p_t_i_o_n is one of the following: 69 70 debug sets RES_DEBUG in ___r_e_s_._o_p_t_i_o_n_s. 71 72 ndots:_n sets a threshold for the number of dots which must 73 appear in a name given to rreess__qquueerryy() (see 74 resolver(3)) before an _i_n_i_t_i_a_l _a_b_s_o_l_u_t_e _q_u_e_r_y will be 75 made. The default for _n is ���1���, meaning that if there 76 are _a_n_y dots in a name, the name will be tried first 77 as an absolute name before any _s_e_a_r_c_h _l_i_s_t elements 78 are appended to it. 79 80 timeout:_n 81 sets the amount of time the resolver will wait for a 82 response from a remote name server before retrying the 83 query via a different name server. Measured in sec��� 84 onds, the default is RES_TIMEOUT (see _<_r_e_s_o_l_v_._h_>). 85 86 attempts:_n 87 sets the number of times the resolver will send a 88 query to its name servers before giving up and return��� 89 ing an error to the calling application. The default 90 is RES_DFLRETRY (see _<_r_e_s_o_l_v_._h_>). 91 92 rotate sets RES_ROTATE in ___r_e_s_._o_p_t_i_o_n_s, which causes round 93 robin selection of nameservers from among those 94 listed. This has the effect of spreading the query 95 load among all listed servers, rather than having all 96 clients try the first listed server first every time. 97 98 no-check-names 99 sets RES_NOCHECKNAME in ___r_e_s_._o_p_t_i_o_n_s, which disables 100 the modern BIND checking of incoming host names and 101 mail names for invalid characters such as underscore 102 (_), non-ASCII, or control characters. 103 104 inet6 sets RES_USE_INET6 in ___r_e_s_._o_p_t_i_o_n_s. This has the 105 effect of trying a AAAA query before an A query inside 106 the _g_e_t_h_o_s_t_b_y_n_a_m_e function, and of mapping IPv4 107 responses in IPv6 ������tunnelled form������ if no AAAA 108 records are found but an A record set exists. 109 110 no-tld-query 111 sets RES_NOTLDQUERY in ___r_e_s_._o_p_t_i_o_n_s. This option 112 causes rreess__nnsseeaarrcchh() to not attempt to resolve a 113 unqualified name as if it were a top level domain 114 (TLD). This option can cause problems if the site has 115 "localhost" as a TLD rather than having localhost on 116 one or more elements of the search list. This option 117 has no effect if neither RES_DEFNAMES or RES_DNSRCH is 118 set. 119 120 The domain and search keywords are mutually exclusive. If more than one 121 instance of these keywords is present, the last instance wins. 122 123 The search keyword of a system���s _r_e_s_o_l_v_._c_o_n_f file can be overridden on a 124 per-process basis by setting the environment variable ���LOCALDOMAIN��� to a 125 space-separated list of search domains. 126 127 The options keyword of a system���s _r_e_s_o_l_v_._c_o_n_f file can be amended on a 128 per-process basis by setting the environment variable ���RES_OPTIONS to a 129 space-separated list of��� rreessoollvveerr options as explained above under 130 options. 131 132 The keyword and value must appear on a single line, and the keyword 133 (e.g., nameserver) must start the line. The value follows the keyword, 134 separated by white space. 135 136FFIILLEESS 137 _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f _<_r_e_s_o_l_v_._h_> 138 139SSEEEE AALLSSOO 140 gethostbyname(3), hostname(7), resolver(3), resolver(5). ���Name Server 141 Operations Guide for BBIINNDD��� 142 1434th Berkeley Distribution November 11, 1993 4th Berkeley Distribution 144