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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 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       In  modern  systems,  even though the host table has been superseded by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  information  for  important hosts on the local network.
              This is useful when DNS is not running, for example during  sys-
              tem 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  cre-
       ated  from the official host data base maintained at the Network Infor-
       mation 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
       # 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.mydomain.org  thishost
       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
       # The following lines are desirable for IPv6 capable hosts
       ::1             localhost ip6-localhost ip6-loopback
       ff02::1         ip6-allnodes
       ff02::2         ip6-allrouters
SEE ALSO
       hostname(1), resolver(3),  host.conf(5),  resolv.conf(5),  resolver(5),
       hostname(7), named(8)
       Internet RFC 952
COLOPHON
       This  page  is  part of release 4.15 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
       https://www.kernel.org/doc/man-pages/.
Linux                             2017-09-15                          HOSTS(5)