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

       hosts - 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...]

       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       In modern systems, even though the host table has been superseded by DNS,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:

              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

       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

       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.


       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

       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.

       # The following lines are desirable for IPv4 capable hosts       localhost

       # is often used for the FQDN of the machine  thishost       foo       bar      master

       # The following lines are desirable for IPv6 capable hosts
       ::1             localhost ip6-localhost ip6-loopback
       ff02::1         ip6-allnodes
       ff02::2         ip6-allrouters

       hostname(1), resolver(3), host.conf(5), resolv.conf(5), resolver(5),
       hostname(7), named(8)

       Internet RFC 952

       This page is part of release 5.13 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

Linux                              2021-03-22                           HOSTS(5)