hosts(5) — Linux manual page


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

NAME         top

       hosts - static table lookup for hostnames

SYNOPSIS         top


DESCRIPTION         top

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       In modern systems, even though the host table has been superseded by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


NOTES         top

       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         top

       # 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

SEE ALSO         top

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

       Internet RFC 952

COLOPHON         top

       This page is part of release 5.09 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                            2020-06-09                         HOSTS(5)

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