man > hosts(5)

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       In  modern systems, even though the host table has been superseded by DNS, it is still widely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 ex‐
              ample 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 In‐
              ternet, 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.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 6.7                          2023-10-31                                     hosts(5)