man5/hosts.5

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  59 In modern systems, even though the host table has been superseded by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