mirror of https://github.com/mkerrisk/man-pages
126 lines
4.2 KiB
Groff
126 lines
4.2 KiB
Groff
.\" Copyright (c) 2000 Manoj Srivastava <srivasta@debian.org>
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.\" Minor polishing, aeb
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.\" Modified, 2002-06-16, Mike Coleman
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.\"
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.TH HOSTS 5 2002-06-16 "Linux" "Linux Programmer's Manual"
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.SH NAME
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hosts \- static table lookup for hostnames
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.SH SYNOPSIS
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.B /etc/hosts
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.SH DESCRIPTION
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This manual page describes the format of the
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.I /etc/hosts
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file.
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This file is a simple text file that associates IP addresses
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with hostnames, one line per IP address.
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For each host a single
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line should be present with the following information:
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.RS
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.PP
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IP_address canonical_hostname [aliases...]
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.RE
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.PP
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Fields of the entry are separated by any number of blanks and/or
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tab characters.
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Text from a "#" character until the end of the line is
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a comment, and is ignored.
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Host names may contain only alphanumeric
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characters, minus signs ("\-"), and periods (".").
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They must begin with an
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alphabetic character and end with an alphanumeric character.
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Optional aliases provide for name changes, alternate spellings,
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shorter hostnames, or generic hostnames (for example,
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.IR localhost ).
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.PP
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The Berkeley Internet Name Domain (BIND) Server implements the
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Internet name server for UNIX systems.
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It augments or replaces the
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.I /etc/hosts
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file or hostname lookup, and frees a host from relying on
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.I /etc/hosts
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being up to date and complete.
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.PP
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In modern systems, even though the host table has been superseded by
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DNS, it is still widely used for:
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.TP
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.B bootstrapping
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Most systems have a small host table containing the name and address
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information for important hosts on the local network.
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This is useful
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when DNS is not running, for example during system bootup.
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.TP
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.B NIS
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Sites that use NIS use the host table as input to the NIS host
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database.
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Even though NIS can be used with DNS, most NIS sites still
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use the host table with an entry for all local hosts as a backup.
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.TP
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.B isolated nodes
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Very small sites that are isolated from the network use the host table
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instead of DNS.
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If the local information rarely changes, and the
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network is not connected to the Internet, DNS offers little
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advantage.
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.SH FILES
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.I /etc/hosts
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.SH NOTES
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Modifications to this file normally take effect immediately,
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except in cases where the file is cached by applications.
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.SS Historical notes
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RFC\ 952 gave the original format for the host table, though it has
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since changed.
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Before the advent of DNS, the host table was the only way of resolving
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hostnames on the fledgling Internet.
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Indeed, this file could be
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created from the official host data base maintained at the Network
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Information Control Center (NIC), though local changes were often
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required to bring it up to date regarding unofficial aliases and/or
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unknown hosts.
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The NIC no longer maintains the hosts.txt files,
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though looking around at the time of writing (circa 2000), there are
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historical hosts.txt files on the WWW.
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I just found three, from 92,
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94, and 95.
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.SH EXAMPLE
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.nf
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127.0.0.1 localhost
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192.168.1.10 foo.mydomain.org foo
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192.168.1.13 bar.mydomain.org bar
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146.82.138.7 master.debian.org master
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209.237.226.90 www.opensource.org
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.fi
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.SH SEE ALSO
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.BR hostname (1),
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.BR resolver (3),
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.BR resolver (5),
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.BR hostname (7),
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.BR named (8)
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Internet RFC\ 952
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.\" .SH AUTHOR
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.\" This manual page was written by Manoj Srivastava <srivasta@debian.org>,
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.\" for the Debian GNU/Linux system.
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