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NAME | SYNOPSIS | DESCRIPTION | FILES | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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HOSTS(5) Linux Programmer's Manual HOSTS(5)
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...]
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In modern systems, even though the host table has been superseded by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:
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.
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.
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.
/etc/hosts
Modifications to this file normally take effect immediately, except
in cases where the file is cached by applications.
Historical notes
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 4.15 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/.
Linux 2017-09-15 HOSTS(5)
Pages that refer to this page: gethostbyname(3), getnameinfo(3), inet(3), host.conf(5), resolv.conf(5), nscd(8), systemd-resolved.service(8)
Copyright and license for this manual page
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HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
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