1HOSTS(5) Linux Programmer's Manual HOSTS(5)
2
6 hosts - The static table lookup for hostnames
7
9 /etc/hosts
10
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 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).
26 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.
31 In modern systems, even though the host table has been superseded by
33 DNS, it is still widely used for:
34 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.
40 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.
45 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.
51
53 /etc/hosts
54
56 Modifications to this file normally take effect immediately, except in
57 cases where the file is cached by applications.
58 Historical Notes
60 RFC 952 gave the original format for the host table, though it has
61 since changed.
62 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.
71
73 127.0.0.1 localhost
74 192.168.1.10 foo.mydomain.org foo
75 192.168.1.13 bar.mydomain.org bar
76 146.82.138.7 master.debian.org master
77 209.237.226.90 www.opensource.org
78
80 hostname(1), resolver(3), resolver(5), hostname(7), named(8), Internet
81 RFC 952
82
84 This page is part of release 3.25 of the Linux man-pages project. A
85 description of the project, and information about reporting bugs, can
86 be found at http://www.kernel.org/doc/man-pages/.
87Linux 2002-06-16 HOSTS(5)