HOSTS(5) Linux Programmer's Manual HOSTS(5)
hosts - static table lookup for hostnames
This manual page describes the format of the /etc/hosts file. This file is a simple text
file that associates IP addresses with hostnames, one line per IP address. For each host
a single line should be present with the following information:
IP_address canonical_hostname [aliases...]
Fields of the entry are separated by any number of blanks and/or tab characters. Text
from a "#" character until the end of the line is a comment, and is ignored. Host names
may contain only alphanumeric characters, minus signs ("-"), and periods ("."). They must
begin with an alphabetic character and end with an alphanumeric character. Optional
aliases provide for name changes, alternate spellings, shorter hostnames, or generic host-
names (for example, localhost).
The Berkeley Internet Name Domain (BIND) Server implements the Internet name server for
UNIX systems. It augments or replaces the /etc/hosts file or hostname lookup, and frees a
host from relying on /etc/hosts being up to date and complete.
In modern systems, even though the host table has been superseded by DNS, it is still
widely used for:
Most systems have a small host table containing the name and address information
for important hosts on the local network. This is useful when DNS is not running,
for example during system bootup.
NIS Sites that use NIS use the host table as input to the NIS host database. Even
though NIS can be used with DNS, most NIS sites still use the host table with an
entry for all local hosts as a backup.
Very small sites that are isolated from the network use the host table instead of
DNS. If the local information rarely changes, and the network is not connected to
the Internet, DNS offers little advantage.
Modifications to this file normally take effect immediately, except in cases where the
file is cached by applications.
RFC 952 gave the original format for the host table, though it has since changed.
Before the advent of DNS, the host table was the only way of resolving hostnames on the
fledgling Internet. Indeed, this file could be created from the official host data base
maintained at the Network Information Control Center (NIC), though local changes were
often required to bring it up to date regarding unofficial aliases and/or unknown hosts.
The NIC no longer maintains the hosts.txt files, though looking around at the time of
writing (circa 2000), there are historical hosts.txt files on the WWW. I just found
three, from 92, 94, and 95.
192.168.1.10 foo.mydomain.org foo
192.168.1.13 bar.mydomain.org bar
220.127.116.11 master.debian.org master
hostname(1), resolver(3), resolver(5), hostname(7), named(8)
Internet RFC 952
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project, and information about reporting bugs, can be found at
Linux 2002-06-16 HOSTS(5)