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       In modern systems, even though the host table has been superseded by DNS, it is still widely used for: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

       # 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)