hosts

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...]

       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       In modern systems, even though the host table has been superseded by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.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 5.08 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                             2020-06-09                          HOSTS(5)