man5/hosts.5

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   2 .\" Copyright (c) 2000 Manoj Srivastava <srivasta@debian.org>
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  25 .\" Minor polishing, aeb
  26 .\" Modified, 2002-06-16, Mike Coleman
  27 .\"
  28 .TH HOSTS 5 2002-06-16 "Linux" "Linux Programmer's Manual"
  29 .SH NAME
  30 hosts \- static table lookup for hostnames
  31 .SH SYNOPSIS
  32 .B /etc/hosts
  33 .SH DESCRIPTION
  34 This manual page describes the format of the
  35 .I /etc/hosts
  36 file.
  37 This file is a simple text file that associates IP addresses
  38 with hostnames, one line per IP address.
  39 For each host a single
  40 line should be present with the following information:
  41 .RS
  42 .PP
  43 IP_address canonical_hostname [aliases...]
  44 .RE
  45 .PP
  46 Fields of the entry are separated by any number of blanks and/or
  47 tab characters.
  48 Text from a "#" character until the end of the line is
  49 a comment, and is ignored.
  50 Host names may contain only alphanumeric
  51 characters, minus signs ("\-"), and periods (".").
  52 They must begin with an
  53 alphabetic character and end with an alphanumeric character.
  54 Optional aliases provide for name changes, alternate spellings,
  55 shorter hostnames, or generic hostnames (for example,
  56 .IR localhost ).
  57 .PP
  58 The Berkeley Internet Name Domain (BIND) Server implements the
  59 Internet name server for UNIX systems.
  60 It augments or replaces the
  61 .I /etc/hosts
  62 file or hostname lookup, and frees a host from relying on
  63 .I /etc/hosts
  64 being up to date and complete.
  65 .PP
  66 In modern systems, even though the host table has been superseded by
  67 DNS, it is still widely used for:
  68 .TP
  69 .B bootstrapping
  70 Most systems have a small host table containing the name and address
  71 information for important hosts on the local network.
  72 This is useful
  73 when DNS is not running, for example during system bootup.
  74 .TP
  75 .B NIS
  76 Sites that use NIS use the host table as input to the NIS host
  77 database.
  78 Even though NIS can be used with DNS, most NIS sites still
  79 use the host table with an entry for all local hosts as a backup.
  80 .TP
  81 .B isolated nodes
  82 Very small sites that are isolated from the network use the host table
  83 instead of DNS.
  84 If the local information rarely changes, and the
  85 network is not connected to the Internet, DNS offers little
  86 advantage.
  87 .SH FILES
  88 .I /etc/hosts
  89 .SH NOTES
  90 Modifications to this file normally take effect immediately,
  91 except in cases where the file is cached by applications.
  92 .SS Historical notes
  93 RFC\ 952 gave the original format for the host table, though it has
  94 since changed.
  95
  96 Before the advent of DNS, the host table was the only way of resolving
  97 hostnames on the fledgling Internet.
  98 Indeed, this file could be
  99 created from the official host data base maintained at the Network
 100 Information Control Center (NIC), though local changes were often
 101 required to bring it up to date regarding unofficial aliases and/or
 102 unknown hosts.
 103 The NIC no longer maintains the hosts.txt files,
 104 though looking around at the time of writing (circa 2000), there are
 105 historical hosts.txt files on the WWW.
 106 I just found three, from 92,
 107 94, and 95.
 108 .SH EXAMPLE
 109 .nf
 110 127.0.0.1       localhost
 111 192.168.1.10    foo.mydomain.org       foo
 112 192.168.1.13    bar.mydomain.org       bar
 113 146.82.138.7    master.debian.org      master
 114 209.237.226.90  www.opensource.org
 115 .fi
 116 .SH SEE ALSO
 117 .BR hostname (1),
 118 .BR resolver (3),
 119 .BR resolver (5),
 120 .BR hostname (7),
 121 .BR named (8)
 122
 123 Internet RFC\ 952
 124 .\" .SH AUTHOR
 125 .\" This manual page was written by Manoj Srivastava <srivasta@debian.org>,
 126 .\" for the Debian GNU/Linux system.