| .\" Copyright (c) 2000 Manoj Srivastava <srivasta@debian.org> |
| .\" |
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| .\" Minor polishing, aeb |
| .\" Modified, 2002-06-16, Mike Coleman |
| .\" |
| .TH HOSTS 5 2017-09-15 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| hosts \- static table lookup for hostnames |
| .SH SYNOPSIS |
| .B /etc/hosts |
| .SH DESCRIPTION |
| This manual page describes the format of the |
| .I /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: |
| .RS |
| .PP |
| IP_address canonical_hostname [aliases...] |
| .RE |
| .PP |
| 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, |
| .IR localhost ). |
| .PP |
| The Berkeley Internet Name Domain (BIND) Server implements the |
| Internet name server for UNIX systems. |
| It augments or replaces the |
| .I /etc/hosts |
| file or hostname lookup, and frees a host from relying on |
| .I /etc/hosts |
| being up to date and complete. |
| .PP |
| In modern systems, even though the host table has been superseded by |
| DNS, it is still widely used for: |
| .TP |
| .B 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. |
| .TP |
| .B 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. |
| .TP |
| .B 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. |
| .SH FILES |
| .I /etc/hosts |
| .SH NOTES |
| Modifications to this file normally take effect immediately, |
| except in cases where the file is cached by applications. |
| .SS Historical notes |
| RFC\ 952 gave the original format for the host table, though it has |
| since changed. |
| .PP |
| 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. |
| .SH EXAMPLE |
| .EX |
| # 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 |
| .EE |
| .SH SEE ALSO |
| .BR hostname (1), |
| .BR resolver (3), |
| .BR host.conf (5), |
| .BR resolv.conf (5), |
| .BR resolver (5), |
| .BR hostname (7), |
| .BR named (8) |
| .PP |
| Internet RFC\ 952 |
| .\" .SH AUTHOR |
| .\" This manual page was written by Manoj Srivastava <srivasta@debian.org>, |
| .\" for the Debian GNU/Linux system. |