hosts - static table lookup for hostnames
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
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
hostname lookup, and frees a host from relying on /etc/hosts
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In modern systems, even though the host table has been superseded by DNS, it is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.
- 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.
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
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
# 127.0.1.1 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
126.96.36.199 master.debian.org master
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
Internet RFC 952
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