Section: Linux Programmer's Manual (5)
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In modern systems, even though the host table has been superseded by DNS, it is still widely used for:
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 22.214.171.124 master.debian.org master 126.96.36.199 www.opensource.org
This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.
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