man7/hostname.7

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  34 .\"     @(#)hostname.7  8.2 (Berkeley) 12/30/93
  35 .\" $FreeBSD: src/share/man/man7/hostname.7,v 1.7 2004/07/03 18:29:23 ru Exp $
  36 .\"
  37 .\" 2008-06-11, mtk, Taken from FreeBSD 6.2 and modified for Linux.
  38 .\"
  39 .TH HOSTNAME 7 2017-05-03 "Linux" "Linux Programmer's Manual"
  40 .SH NAME
  41 hostname \- hostname resolution description
  42 .SH DESCRIPTION
  43 Hostnames are domains, where a domain is a hierarchical, dot-separated
  44 list of subdomains; for example, the machine "monet", in the "example"
  45 subdomain of the "com" domain would be represented as "monet.example.com".
  46 .PP
  47 Each element of the hostname must be from 1 to 63 characters long and the
  48 entire hostname, including the dots, can be at most 253 characters long.
  49 Valid characters for hostnames are
  50 .BR ASCII (7)
  51 letters from
  52 .I a
  53 to
  54 .IR z ,
  55 the digits from
  56 .I 0
  57 to
  58 .IR 9 ,
  59 and the hyphen (\-).
  60 A hostname may not start with a hyphen.
  61 .PP
  62 Hostnames are often used with network client and server programs,
  63 which must generally translate the name to an address for use.
  64 (This task is generally performed by either
  65 .BR getaddrinfo (3)
  66 or the obsolete
  67 .BR gethostbyname (3).)
  68 .PP
  69 Hostnames are resolved by the NSS framework in glibc according
  70 to the
  71 .B hosts
  72 configuration in
  73 .BR nsswitch.conf .
  74 The DNS-based name resolver
  75 (in the
  76 .B dns
  77 NSS service module) resolves them in the following fashion.
  78 .PP
  79 If the name consists of a single component, that is, contains no dot,
  80 and if the environment variable
  81 .B HOSTALIASES
  82 is set to the name of a file,
  83 that file is searched for any string matching the input hostname.
  84 The file should consist of lines made up of two white-space separated strings,
  85 the first of which is the hostname alias,
  86 and the second of which is the complete hostname
  87 to be substituted for that alias.
  88 If a case-insensitive match is found between the hostname to be resolved
  89 and the first field of a line in the file, the substituted name is looked
  90 up with no further processing.
  91 .PP
  92 If the input name ends with a trailing dot,
  93 the trailing dot is removed,
  94 and the remaining name is looked up with no further processing.
  95 .PP
  96 If the input name does not end with a trailing dot, it is looked up
  97 by searching through a list of domains until a match is found.
  98 The default search list includes first the local domain,
  99 then its parent domains with at least 2 name components (longest first).
 100 For example,
 101 in the domain cs.example.com, the name lithium.cchem will be checked first
 102 as lithium.cchem.cs.example and then as lithium.cchem.example.com.
 103 lithium.cchem.com will not be tried, as there is only one component
 104 remaining from the local domain.
 105 The search path can be changed from the default
 106 by a system-wide configuration file (see
 107 .BR resolver (5)).
 108 .SH SEE ALSO
 109 .BR getaddrinfo (3),
 110 .BR gethostbyname (3),
 111 .BR nsswitch.conf (5),
 112 .BR resolver (5),
 113 .BR mailaddr (7),
 114 .BR named (8)
 115 .PP
 116 .UR http://www.ietf.org\:/rfc\:/rfc1123.txt
 117 IETF RFC\ 1123
 118 .UE
 119 .PP
 120 .UR http://www.ietf.org\:/rfc\:/rfc1178.txt
 121 IETF RFC\ 1178
 122 .UE
 123 .\" .SH HISTORY
 124 .\" Hostname appeared in
 125 .\" 4.2BSD.