HOSTS(5)                            Linux Programmer's Manual                            HOSTS(5)



NAME
       hosts - static table lookup for hostnames

SYNOPSIS
       /etc/hosts

DESCRIPTION
       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 host‐
       names (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       In modern systems, even though the host table has been superseded  by  DNS,  it  is  still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.

FILES
       /etc/hosts

NOTES
       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.

EXAMPLE
       127.0.0.1       localhost
       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

SEE ALSO
       hostname(1), resolver(3), resolver(5), hostname(7), named(8)

       Internet RFC 952

COLOPHON
       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/.



Linux                                       2002-06-16                                   HOSTS(5)