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1 | .\" Copyright (c) 2000 Manoj Srivastava <srivasta@debian.org> |
2 | .\" | |
1dd72f9c | 3 | .\" %%%LICENSE_START(GPLv2+_DOC_FULL) |
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4 | .\" This is free documentation; you can redistribute it and/or |
5 | .\" modify it under the terms of the GNU General Public License as | |
6 | .\" published by the Free Software Foundation; either version 2 of | |
7 | .\" the License, or (at your option) any later version. | |
8 | .\" | |
9 | .\" The GNU General Public License's references to "object code" | |
10 | .\" and "executables" are to be interpreted as the output of any | |
11 | .\" document formatting or typesetting system, including | |
12 | .\" intermediate and printed output. | |
13 | .\" | |
14 | .\" This manual is distributed in the hope that it will be useful, | |
15 | .\" but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
17 | .\" GNU General Public License for more details. | |
18 | .\" | |
19 | .\" You should have received a copy of the GNU General Public | |
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20 | .\" License along with this manual; if not, see |
21 | .\" <http://www.gnu.org/licenses/>. | |
6a8d8745 | 22 | .\" %%%LICENSE_END |
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23 | .\" |
24 | .\" Minor polishing, aeb | |
25 | .\" Modified, 2002-06-16, Mike Coleman | |
26 | .\" | |
4b8c67d9 | 27 | .TH HOSTS 5 2017-09-15 "Linux" "Linux Programmer's Manual" |
fea681da | 28 | .SH NAME |
eebc6bfc | 29 | hosts \- static table lookup for hostnames |
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30 | .SH SYNOPSIS |
31 | .B /etc/hosts | |
32 | .SH DESCRIPTION | |
c13182ef | 33 | This manual page describes the format of the |
fea681da | 34 | .I /etc/hosts |
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35 | file. |
36 | This file is a simple text file that associates IP addresses | |
37 | with hostnames, one line per IP address. | |
38 | For each host a single | |
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39 | line should be present with the following information: |
40 | .RS | |
41 | .PP | |
80ee1d97 | 42 | IP_address canonical_hostname [aliases...] |
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43 | .RE |
44 | .PP | |
45 | Fields of the entry are separated by any number of blanks and/or | |
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46 | tab characters. |
47 | Text from a "#" character until the end of the line is | |
48 | a comment, and is ignored. | |
49 | Host names may contain only alphanumeric | |
50 | characters, minus signs ("\-"), and periods ("."). | |
51 | They must begin with an | |
fea681da | 52 | alphabetic character and end with an alphanumeric character. |
80ee1d97 | 53 | Optional aliases provide for name changes, alternate spellings, |
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54 | shorter hostnames, or generic hostnames (for example, |
55 | .IR localhost ). | |
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56 | .PP |
57 | The Berkeley Internet Name Domain (BIND) Server implements the | |
008f1ecc | 58 | Internet name server for UNIX systems. |
c13182ef | 59 | It augments or replaces the |
fea681da | 60 | .I /etc/hosts |
ddaec46d | 61 | file or hostname lookup, and frees a host from relying on |
fea681da | 62 | .I /etc/hosts |
c13182ef | 63 | being up to date and complete. |
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64 | .PP |
65 | In modern systems, even though the host table has been superseded by | |
66 | DNS, it is still widely used for: | |
67 | .TP | |
68 | .B bootstrapping | |
69 | Most systems have a small host table containing the name and address | |
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70 | information for important hosts on the local network. |
71 | This is useful | |
72 | when DNS is not running, for example during system bootup. | |
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73 | .TP |
74 | .B NIS | |
75 | Sites that use NIS use the host table as input to the NIS host | |
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76 | database. |
77 | Even though NIS can be used with DNS, most NIS sites still | |
78 | use the host table with an entry for all local hosts as a backup. | |
79 | .TP | |
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80 | .B isolated nodes |
81 | Very small sites that are isolated from the network use the host table | |
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82 | instead of DNS. |
83 | If the local information rarely changes, and the | |
fea681da | 84 | network is not connected to the Internet, DNS offers little |
c13182ef | 85 | advantage. |
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86 | .SH FILES |
87 | .I /etc/hosts | |
19c98696 | 88 | .SH NOTES |
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89 | Modifications to this file normally take effect immediately, |
90 | except in cases where the file is cached by applications. | |
73d8cece | 91 | .SS Historical notes |
331da7c3 | 92 | RFC\ 952 gave the original format for the host table, though it has |
80ee1d97 | 93 | since changed. |
eabf3ae5 | 94 | .PP |
fea681da | 95 | Before the advent of DNS, the host table was the only way of resolving |
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96 | hostnames on the fledgling Internet. |
97 | Indeed, this file could be | |
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98 | created from the official host data base maintained at the Network |
99 | Information Control Center (NIC), though local changes were often | |
100 | required to bring it up to date regarding unofficial aliases and/or | |
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101 | unknown hosts. |
102 | The NIC no longer maintains the hosts.txt files, | |
fea681da | 103 | though looking around at the time of writing (circa 2000), there are |
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104 | historical hosts.txt files on the WWW. |
105 | I just found three, from 92, | |
fea681da | 106 | 94, and 95. |
2b2581ee | 107 | .SH EXAMPLE |
a2b7a144 | 108 | .EX |
8528c989 | 109 | # The following lines are desirable for IPv4 capable hosts |
2b2581ee | 110 | 127.0.0.1 localhost |
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111 | |
112 | # 127.0.1.1 is often used for the FQDN of the machine | |
113 | 127.0.1.1 thishost.mydomain.org thishost | |
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114 | 192.168.1.10 foo.mydomain.org foo |
115 | 192.168.1.13 bar.mydomain.org bar | |
116 | 146.82.138.7 master.debian.org master | |
117 | 209.237.226.90 www.opensource.org | |
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118 | |
119 | # The following lines are desirable for IPv6 capable hosts | |
120 | ::1 localhost ip6-localhost ip6-loopback | |
121 | ff02::1 ip6-allnodes | |
122 | ff02::2 ip6-allrouters | |
a2b7a144 | 123 | .EE |
47297adb | 124 | .SH SEE ALSO |
fea681da | 125 | .BR hostname (1), |
2da61423 | 126 | .BR resolver (3), |
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127 | .BR host.conf (5), |
128 | .BR resolv.conf (5), | |
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129 | .BR resolver (5), |
130 | .BR hostname (7), | |
173fe7e7 | 131 | .BR named (8) |
eabf3ae5 | 132 | .PP |
331da7c3 | 133 | Internet RFC\ 952 |
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134 | .\" .SH AUTHOR |
135 | .\" This manual page was written by Manoj Srivastava <srivasta@debian.org>, | |
136 | .\" for the Debian GNU/Linux system. |