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...]

       The  IP  address  can conform to either IPv4 or IPv6.  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).  If required, a host may have two separate entries in this file; one for each version of  the
       Internet Protocol (IPv4 and IPv6).

       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       In modern systems, even though the host table has been superseded by DNS, it is still widely used for: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.

EXAMPLES

       # 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.example.org   thishost
       192.168.1.10    foo.example.org        foo
       192.168.1.13    bar.example.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

Linux man-pages 6.7                                2023-10-31                                           hosts(5)