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 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 com-
       plete.

       In modern systems, even though the host table has been superseded by DNS, it is still widely used for: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 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2002-06-16                                                   HOSTS(5)