hosts(5) — Linux manual page

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       In modern systems, even though the host table has been superseded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

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                       hosts(5)

Pages that refer to this page: getent(1), gethostbyname(3), getnameinfo(3), inet(3), host.conf(5), resolv.conf(5), systemd.system-credentials(7), nscd(8), systemd-resolved.service(8)

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