HOSTS(5)                  (2020-06-09)                   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 con-
          tain 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 host-
          names, 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 com-
          plete.

          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          superseded by DNS, it is still widely used for: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

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               the host table instead of DNS.  If the local informa-
               tion 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 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 his-
          torical 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.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 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be

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          found at https://www.kernel.org/doc/man-pages/.

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