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HOSTS(5) Linux Programmer's Manual HOSTS(5)
hosts - static table lookup for hostnames
/etc/hosts
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 hostnames (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In modern systems, even though the host table has been superseded by DNS, it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:
bootstrapping
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.
isolated nodes
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.
/etc/hosts
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.
127.0.0.1 localhost
192.168.1.10 foo.mydomain.org foo
192.168.1.13 bar.mydomain.org bar
146.82.138.7 master.debian.org master
209.237.226.90 www.opensource.org
hostname(1), resolver(3), resolver(5), hostname(7), named(8), Internet RFC 952
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2002-06-16 HOSTS(5)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface