hosts

hosts(5) File Formats 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...]

   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   In modern systems, even though the host table has been superseded by DNS, it is still widely used for: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  Inter
          net, 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 main
   tained 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 6.9.1 2024-05-02 hosts(5)