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...]
The IP address can conform to either IPv4 or IPv6. 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). If required, a
host may have two separate entries in this file; one for each
version of the Internet Protocol (IPv4 and IPv6).
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In modern systems, even though the host table has been superseded by DNS, it is still widely used for: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.
NISSites 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.
# The following lines are desirable for IPv4 capable hosts 127.0.0.1 localhost # 127.0.1.1 is often used for the FQDN of the machine 127.0.1.1 thishost.mydomain.org thishost 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 # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6−localhost ip6−loopback ff02::1 ip6−allnodes ff02::2 ip6−allrouters
hostname(1), resolver(3), host.conf(5), resolv.conf(5), resolver(5), hostname(7), named(8)
Internet RFC 952
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (c) 2000 Manoj Srivastava <srivastadebian.org> %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END Minor polishing, aeb Modified, 2002-06-16, Mike Coleman |