1HOSTS(5)                   Linux Programmer's Manual                  HOSTS(5)
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NAME

6       hosts - static table lookup for hostnames
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SYNOPSIS

9       /etc/hosts
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DESCRIPTION

12       This  manual  page  describes  the format of the /etc/hosts file.  This
13       file is a simple text file that associates IP addresses with hostnames,
14       one line per IP address.  For each host a single line should be present
15       with the following information:
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17              IP_address canonical_hostname [aliases...]
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19       Fields of the entry are separated by any number of  blanks  and/or  tab
20       characters.   Text  from a "#" character until the end of the line is a
21       comment, and is ignored.  Host  names  may  contain  only  alphanumeric
22       characters, minus signs ("-"), and periods (".").  They must begin with
23       an  alphabetic  character  and  end  with  an  alphanumeric  character.
24       Optional aliases provide for name changes, alternate spellings, shorter
25       hostnames, or generic hostnames (for example, localhost).
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27       The Berkeley Internet Name Domain (BIND) Server implements the Internet
28       name  server  for UNIX systems.  It augments or replaces the /etc/hosts
29       file or hostname lookup, and frees a host from  relying  on  /etc/hosts
30       being up to date and complete.
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32       In  modern  systems,  even though the host table has been superseded by
33       DNS, it is still widely used for:
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35       bootstrapping
36              Most systems have a small host table  containing  the  name  and
37              address  information  for  important hosts on the local network.
38              This is useful when DNS is not running, for example during  sys‐
39              tem bootup.
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41       NIS    Sites  that  use NIS use the host table as input to the NIS host
42              database.  Even though NIS can be used with DNS, most NIS  sites
43              still  use the host table with an entry for all local hosts as a
44              backup.
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46       isolated nodes
47              Very small sites that are isolated from the network use the host
48              table  instead of DNS.  If the local information rarely changes,
49              and the network is not connected to  the  Internet,  DNS  offers
50              little advantage.
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FILES

53       /etc/hosts
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NOTES

56       Modifications  to this file normally take effect immediately, except in
57       cases where the file is cached by applications.
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59   Historical notes
60       RFC 952 gave the original format for the  host  table,  though  it  has
61       since changed.
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63       Before  the advent of DNS, the host table was the only way of resolving
64       hostnames on the fledgling Internet.  Indeed, this file could  be  cre‐
65       ated  from the official host data base maintained at the Network Infor‐
66       mation Control Center (NIC), though local changes were  often  required
67       to  bring  it  up  to  date regarding unofficial aliases and/or unknown
68       hosts.  The NIC no longer maintains the hosts.txt files, though looking
69       around  at  the  time  of  writing  (circa  2000), there are historical
70       hosts.txt files on the WWW.  I just found three, from 92, 94, and 95.
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EXAMPLE

73       # The following lines are desirable for IPv4 capable hosts
74       127.0.0.1       localhost
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76       # 127.0.1.1 is often used for the FQDN of the machine
77       127.0.1.1       thishost.mydomain.org  thishost
78       192.168.1.10    foo.mydomain.org       foo
79       192.168.1.13    bar.mydomain.org       bar
80       146.82.138.7    master.debian.org      master
81       209.237.226.90  www.opensource.org
82
83       # The following lines are desirable for IPv6 capable hosts
84       ::1             localhost ip6-localhost ip6-loopback
85       ff02::1         ip6-allnodes
86       ff02::2         ip6-allrouters
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SEE ALSO

89       hostname(1), resolver(3),  host.conf(5),  resolv.conf(5),  resolver(5),
90       hostname(7), named(8)
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92       Internet RFC 952
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COLOPHON

95       This  page  is  part of release 4.15 of the Linux man-pages project.  A
96       description of the project, information about reporting bugs,  and  the
97       latest     version     of     this    page,    can    be    found    at
98       https://www.kernel.org/doc/man-pages/.
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102Linux                             2017-09-15                          HOSTS(5)
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