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NAME | SYNOPSIS | DESCRIPTION | FILES | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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hosts(5) File Formats 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...]
The IP address can conform to either IPv4 or IPv6. 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). If required, a host may have two separate entries in
this file; one for each version of the Internet Protocol (IPv4 and
IPv6).
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In modern systems, even though the host table has been superseded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.example.org thishost
192.168.1.10 foo.example.org foo
192.168.1.13 bar.example.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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 hosts(5)
Pages that refer to this page: getent(1), gethostbyname(3), getnameinfo(3), inet(3), host.conf(5), resolv.conf(5), systemd.system-credentials(7), nscd(8), systemd-resolved.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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