111 lines
4.7 KiB
Groff
111 lines
4.7 KiB
Groff
.\" $NetBSD: hostname.7,v 1.2 1997/04/13 10:50:51 mrg Exp $
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.\"
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.\" Copyright (c) 1987 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms are permitted
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.\" provided that the above copyright notice and this paragraph are
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.\" duplicated in all such forms and that any documentation,
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.\" advertising materials, and other materials related to such
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.\" distribution and use acknowledge that the software was developed
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.\" by the University of California, Berkeley. The name of the
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.\" University may not be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.\" @(#)hostname.7 6.4 (Berkeley) 1/16/90
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.\"
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.TH HOSTNAME 7 "February 16, 1994"
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.UC 5
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.SH NAME
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hostname \- host name resolution description
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.SH DESCRIPTION
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Hostnames are domains. A domain is a hierarchical, dot-separated list
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of subdomains. For example, the machine \fImonet\fP, in the \fIBerkeley\fP
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subdomain of the \fIEDU\fP subdomain of the Internet Domain Name System
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would be represented as
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.br
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\fImonet\fP.\fIBerkeley\fP.\fIEDU\fP
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.br
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(with no trailing dot).
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.PP
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Hostnames are often used with network client and server programs,
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which must generally translate the name to an address for use.
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(This task is usually performed by the library routine
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.IR gethostbyname (3).)
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The default method for resolving hostnames by the Internet name resolver is
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to follow \s-1RFC\s+1 1535's security recommendations. Actions can be taken
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by the administrator to override these recommendations and to have the
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resolver behave the same as earlier, non-\s-1RFC\s+1 1535 resolvers.
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.PP
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The default method (using \s-1RFC\s+1 1535 guidelines) follows:
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.PP
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If the name consists of a single component, i.e. contains no dot, and if the
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environment variable ``\s-1HOSTALIASES\s+1'' is set to the name of a file,
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that file is searched for a string matching the input hostname. The file
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should consist of lines made up of two strings separated by white-space, the
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first of which is the hostname alias, and the second of which is the complete
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hostname to be substituted for that alias. If a case-insensitive match is
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found between the hostname to be resolved and the first field of a line in
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the file, the substituted name is looked up with no further processing.
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.PP
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If there is at least one dot in the name, then the name is first tried as
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is. The number of dots to cause this action is configurable by setting the
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threshold using the ``\fIndots\fP'' option in
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.I /etc/resolv.conf
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(default: \fI1\fP). If the name ends with a dot, the trailing dot is
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removed, and the remaining name is looked up (regardless of the setting of
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the 'ndots' option) and no further processing is done.
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.PP
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If the input name does not end with a trailing dot, it is looked up by
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searching through a list of domains until a match is found. If neither the
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search option in the
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.I /etc/resolv.conf
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file or the ``\s-1LOCALDOMAIN\s+1'' environment variable is used, then the
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search list of domains contains only the full domain specified by the domain
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option (in
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.IR /etc/resolv.conf )
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or the domain used in the local hostname (see
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.IR hostname (1)
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and
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.IR resolver (5)).
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For example, if the ``\fIdomain\fP'' option is set to \fICS.Berkeley.EDU\fP,
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then only CS.Berkeley.EDU will be in the search list and will be the only
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domain appended to the partial hostname, for example, ``\fIlithium\fP'',
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making \fIlithium.CS.Berkeley.EDU\fP the only name to be tried using the
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search list.
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.PP
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If the search option is used in
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.I /etc/resolv.conf
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or the environment variable, ``\s-1LOCALDOMAIN\s+1'' is set by the user, then
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the search list will include what is set by these methods. For
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example, if the ``\fIsearch\fP'' option contained
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.br
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\fICS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU\fP
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.br
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then the partial hostname (e.g., ``\fIlithium\fP'') will be tried with each
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domainname appended (in the same order specified). The resulting hostnames
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that would be tried are:
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.nf
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\fIlithium.CS.Berkeley.EDU\fP
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\fIlithium.CChem.Berkeley.EDU\fP
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\fIlithium.Berkeley.EDU\fP
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.fi
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.PP
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The environment variable ``\s-1LOCALDOMAIN\s+1'' overrides the
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``\fIsearch\fP'' and ``\fIdomain\fP'' options, and if both search and domain
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options are present in the resolver configuration file, then only the last
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one listed is used (see
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.IR resolver (5)).
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.PP
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If the name was not previously tried ``as is'' (i.e., it fell below the
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``\fIndots\fP'' threshold or did not contain a dot), then the name as
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originally provided is attempted.
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.SH SEE ALSO
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.IR gethostbyname (3),
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.IR resolver (5),
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.IR mailaddr (7),
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.IR named (8)
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