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

       hosts - The 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
       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 alphanu-
       meric 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 aug-
       ments 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       In modern systems, even though the host table has been superseded by DNS, it is still widely used for:

              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  advan-


       Modifications to this file normally take effect immediately, except in cases where the file is cached by appli-

   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 Con-
       trol 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

EXAMPLE       localhost       foo       bar      master

       hostname(1), resolver(3), resolver(5), hostname(7), named(8), Internet RFC 952

       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at

Linux                             2002-06-16                          HOSTS(5)