1HOSTNAME(7) FreeBSD Miscellaneous Information Manual HOSTNAME(7) 2 3NNAAMMEE 4 hhoossttnnaammee -- host name resolution description 5 6DDEESSCCRRIIPPTTIIOONN 7 Hostnames are domains. A domain is a hierarchical, dot-separated list of 8 subdomains. For example, the machine ``monet'', in the ``Berkeley'' sub- 9 domain of the ``EDU'' subdomain of the Internet Domain Name System would 10 be represented as 11 12 monet.Berkeley.EDU 13 14 (with no trailing dot). 15 16 Hostnames are often used with network client and server programs, which 17 must generally translate the name to an address for use. (This task is 18 usually performed by the library routine gethostbyname(3).) The default 19 method for resolving hostnames by the Internet name resolver is to follow 20 RFC 1535's security recommendations. Actions can be taken by the admin- 21 istrator to override these recommendations and to have the resolver 22 behave the same as earlier, non-RFC 1535 resolvers. 23 24 The default method (using RFC 1535 guidelines) follows: 25 26 If the name consists of a single component, i.e. contains no dot, and if 27 the environment variable ``HOSTALIASES'' is set to the name of a file, 28 that file is searched for a string matching the input hostname. The file 29 should consist of lines made up of two strings separated by white-space, 30 the first of which is the hostname alias, and the second of which is the 31 complete hostname to be substituted for that alias. If a case-insensi- 32 tive match is found between the hostname to be resolved and the first 33 field of a line in the file, the substituted name is looked up with no 34 further processing. 35 36 If there is at least one dot in the name, then the name is first tried 37 ``as-is''. The number of dots to cause this action is configurable by 38 setting the threshold using the ``ndots'' option in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f 39 (default: 1). If the name ends with a dot, the trailing dot is removed, 40 and the remaining name is looked up (regardless of the setting of the 41 ndots option), without further processing. 42 43 If the input name does not end with a trailing dot, it is looked up by 44 searching through a list of domains until a match is found. If neither 45 the search option in the _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f file or the ``LOCALDOMAIN'' 46 environment variable is used, then the search list of domains contains 47 only the full domain specified by the domain option (in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f) 48 or the domain used in the local hostname. For example, if the ``domain'' 49 option is set to CS.Berkeley.EDU, then only CS.Berkeley.EDU will be in 50 the search list, and this will be the only domain appended to the partial 51 hostname. For example, if ``lithium'' is the name to be resolved, this 52 would make lithium.CS.Berkeley.EDU the only name to be tried using the 53 search list. 54 55 If the search option is used in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f or the environment vari- 56 able ``LOCALDOMAIN'' is set by the user, then the search list will 57 include what is set by these methods. For example, if the ``search'' 58 option contained 59 60 CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU 61 62 then the partial hostname (e.g., ``lithium'') will be tried with _e_a_c_h 63 domain name appended (in the same order specified); the resulting host- 64 names that would be tried are: 65 66 lithium.CS.Berkeley.EDU 67 lithium.CChem.Berkeley.EDU 68 lithium.Berkeley.EDU 69 70 The environment variable ``LOCALDOMAIN'' overrides the ``search'' and 71 ``domain'' options, and if both search and domain options are present in 72 the resolver configuration file, then only the _l_a_s_t one listed is used 73 (see resolver(5)). 74 75 If the name was not previously tried ``as-is'' (i.e., it fell below the 76 ``ndots'' threshold or did not contain a dot), then the name as origi- 77 nally provided is attempted. 78 79EENNVVIIRROONNMMEENNTT 80 LOCALDOMAIN Affects domains appended to partial hostnames. 81 82 HOSTALIASES Name of file containing (_h_o_s_t _a_l_i_a_s, _f_u_l_l _h_o_s_t_n_a_m_e) 83 pairs. 84 85FFIILLEESS 86 /etc/resolv.conf See resolve(5). 87 88SSEEEE AALLSSOO 89 gethostbyname(3), resolver(5), mailaddr(7), 90 914th Berkeley Distribution February 16, 1994 4th Berkeley Distribution 92