1HOSTS(5) Linux Programmer's Manual HOSTS(5)
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6 hosts - static table lookup for hostnames
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9 /etc/hosts
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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:
16 IP_address canonical_hostname [aliases...]
18 The IP address can conform to either IPv4 or IPv6. Fields of the entry
20 are separated by any number of blanks and/or tab characters. Text from
21 a "#" character until the end of the line is a comment, and is ignored.
22 Host names may contain only alphanumeric characters, minus signs ("-"),
23 and periods ("."). They must begin with an alphabetic character and
24 end with an alphanumeric character. Optional aliases provide for name
25 changes, alternate spellings, shorter hostnames, or generic hostnames
26 (for example, localhost). If required, a host may have two separate
27 entries in this file; one for each version of the Internet Protocol
28 (IPv4 and IPv6).
29 The Berkeley Internet Name Domain (BIND) Server implements the Internet
31 name server for UNIX systems. It augments or replaces the /etc/hosts
32 file or hostname lookup, and frees a host from relying on /etc/hosts
33 being up to date and complete.
34 In modern systems, even though the host table has been superseded by
36 DNS, it is still widely used for:
37 bootstrapping
39 Most systems have a small host table containing the name and ad‐
40 dress information for important hosts on the local network.
41 This is useful when DNS is not running, for example during sys‐
42 tem bootup.
43 NIS Sites that use NIS use the host table as input to the NIS host
45 database. Even though NIS can be used with DNS, most NIS sites
46 still use the host table with an entry for all local hosts as a
47 backup.
48 isolated nodes
50 Very small sites that are isolated from the network use the host
51 table instead of DNS. If the local information rarely changes,
52 and the network is not connected to the Internet, DNS offers
53 little advantage.
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56 /etc/hosts
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59 Modifications to this file normally take effect immediately, except in
60 cases where the file is cached by applications.
61 Historical notes
63 RFC 952 gave the original format for the host table, though it has
64 since changed.
65 Before the advent of DNS, the host table was the only way of resolving
67 hostnames on the fledgling Internet. Indeed, this file could be cre‐
68 ated from the official host data base maintained at the Network Infor‐
69 mation Control Center (NIC), though local changes were often required
70 to bring it up to date regarding unofficial aliases and/or unknown
71 hosts. The NIC no longer maintains the hosts.txt files, though looking
72 around at the time of writing (circa 2000), there are historical
73 hosts.txt files on the WWW. I just found three, from 92, 94, and 95.
74
76 # The following lines are desirable for IPv4 capable hosts
77 127.0.0.1 localhost
78 # 127.0.1.1 is often used for the FQDN of the machine
80 127.0.1.1 thishost.mydomain.org thishost
81 192.168.1.10 foo.mydomain.org foo
82 192.168.1.13 bar.mydomain.org bar
83 146.82.138.7 master.debian.org master
84 209.237.226.90 www.opensource.org
85 # The following lines are desirable for IPv6 capable hosts
87 ::1 localhost ip6-localhost ip6-loopback
88 ff02::1 ip6-allnodes
89 ff02::2 ip6-allrouters
90
92 hostname(1), resolver(3), host.conf(5), resolv.conf(5), resolver(5),
93 hostname(7), named(8)
94 Internet RFC 952
96
98 This page is part of release 5.12 of the Linux man-pages project. A
99 description of the project, information about reporting bugs, and the
100 latest version of this page, can be found at
101 https://www.kernel.org/doc/man-pages/.
102Linux 2021-03-22 HOSTS(5)