1*5bbd2a12SchristosHOSTNAME(7) FreeBSD Miscellaneous Information Manual HOSTNAME(7) 2b5677b36Schristos 3b5677b36SchristosNNAAMMEE 4*5bbd2a12Schristos hhoossttnnaammee -- host name resolution description 5b5677b36Schristos 6b5677b36SchristosDDEESSCCRRIIPPTTIIOONN 7b5677b36Schristos Hostnames are domains. A domain is a hierarchical, dot-separated list of 8*5bbd2a12Schristos subdomains. For example, the machine ``monet'', in the ``Berkeley'' sub- 9*5bbd2a12Schristos domain of the ``EDU'' subdomain of the Internet Domain Name System would 10*5bbd2a12Schristos be represented as 11b5677b36Schristos 12b5677b36Schristos monet.Berkeley.EDU 13b5677b36Schristos 14b5677b36Schristos (with no trailing dot). 15b5677b36Schristos 16b5677b36Schristos Hostnames are often used with network client and server programs, which 17b5677b36Schristos must generally translate the name to an address for use. (This task is 18b5677b36Schristos usually performed by the library routine gethostbyname(3).) The default 19b5677b36Schristos method for resolving hostnames by the Internet name resolver is to follow 20*5bbd2a12Schristos RFC 1535's security recommendations. Actions can be taken by the admin- 21b5677b36Schristos istrator to override these recommendations and to have the resolver 22b5677b36Schristos behave the same as earlier, non-RFC 1535 resolvers. 23b5677b36Schristos 24b5677b36Schristos The default method (using RFC 1535 guidelines) follows: 25b5677b36Schristos 26b5677b36Schristos If the name consists of a single component, i.e. contains no dot, and if 27*5bbd2a12Schristos the environment variable ``HOSTALIASES'' is set to the name of a file, 28*5bbd2a12Schristos that file is searched for a string matching the input hostname. The file 29b5677b36Schristos should consist of lines made up of two strings separated by white-space, 30b5677b36Schristos the first of which is the hostname alias, and the second of which is the 31*5bbd2a12Schristos complete hostname to be substituted for that alias. If a case-insensi- 32b5677b36Schristos tive match is found between the hostname to be resolved and the first 33b5677b36Schristos field of a line in the file, the substituted name is looked up with no 34b5677b36Schristos further processing. 35b5677b36Schristos 36b5677b36Schristos If there is at least one dot in the name, then the name is first tried 37*5bbd2a12Schristos ``as-is''. The number of dots to cause this action is configurable by 38*5bbd2a12Schristos setting the threshold using the ``ndots'' option in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f 39*5bbd2a12Schristos (default: 1). If the name ends with a dot, the trailing dot is removed, 40*5bbd2a12Schristos and the remaining name is looked up (regardless of the setting of the 41*5bbd2a12Schristos ndots option), without further processing. 42b5677b36Schristos 43b5677b36Schristos If the input name does not end with a trailing dot, it is looked up by 44b5677b36Schristos searching through a list of domains until a match is found. If neither 45*5bbd2a12Schristos the search option in the _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f file or the ``LOCALDOMAIN'' 46*5bbd2a12Schristos environment variable is used, then the search list of domains contains 47*5bbd2a12Schristos only the full domain specified by the domain option (in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f) 48*5bbd2a12Schristos or the domain used in the local hostname. For example, if the ``domain'' 49b5677b36Schristos option is set to CS.Berkeley.EDU, then only CS.Berkeley.EDU will be in 50b5677b36Schristos the search list, and this will be the only domain appended to the partial 51*5bbd2a12Schristos hostname. For example, if ``lithium'' is the name to be resolved, this 52b5677b36Schristos would make lithium.CS.Berkeley.EDU the only name to be tried using the 53b5677b36Schristos search list. 54b5677b36Schristos 55*5bbd2a12Schristos 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*5bbd2a12Schristos able ``LOCALDOMAIN'' is set by the user, then the search list will 57*5bbd2a12Schristos include what is set by these methods. For example, if the ``search'' 58*5bbd2a12Schristos option contained 59b5677b36Schristos 60b5677b36Schristos CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU 61b5677b36Schristos 62*5bbd2a12Schristos then the partial hostname (e.g., ``lithium'') will be tried with _e_a_c_h 63*5bbd2a12Schristos domain name appended (in the same order specified); the resulting host- 64b5677b36Schristos names that would be tried are: 65b5677b36Schristos 66b5677b36Schristos lithium.CS.Berkeley.EDU 67b5677b36Schristos lithium.CChem.Berkeley.EDU 68b5677b36Schristos lithium.Berkeley.EDU 69b5677b36Schristos 70*5bbd2a12Schristos The environment variable ``LOCALDOMAIN'' overrides the ``search'' and 71*5bbd2a12Schristos ``domain'' options, and if both search and domain options are present in 72b5677b36Schristos the resolver configuration file, then only the _l_a_s_t one listed is used 73b5677b36Schristos (see resolver(5)). 74b5677b36Schristos 75*5bbd2a12Schristos If the name was not previously tried ``as-is'' (i.e., it fell below the 76*5bbd2a12Schristos ``ndots'' threshold or did not contain a dot), then the name as origi- 77*5bbd2a12Schristos nally provided is attempted. 78b5677b36Schristos 79b5677b36SchristosEENNVVIIRROONNMMEENNTT 80b5677b36Schristos LOCALDOMAIN Affects domains appended to partial hostnames. 81b5677b36Schristos 82b5677b36Schristos 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) 83b5677b36Schristos pairs. 84b5677b36Schristos 85b5677b36SchristosFFIILLEESS 86b5677b36Schristos /etc/resolv.conf See resolve(5). 87b5677b36Schristos 88b5677b36SchristosSSEEEE AALLSSOO 89b5677b36Schristos gethostbyname(3), resolver(5), mailaddr(7), 90b5677b36Schristos 91b5677b36Schristos4th Berkeley Distribution February 16, 1994 4th Berkeley Distribution 92