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



NAME
       hosts - The static table lookup for hostnames

SYNOPSIS
       /etc/hosts

DESCRIPTION
       This  manual page describes the format of the /etc/hosts file.  This file is a sim-
       ple 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       In modern systems, even though the host table has been superseded  by  DNS,  it  is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 infor-
              mation 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  ta-
              ble 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 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2002-06-16                          HOSTS(5)

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