1.\" $NetBSD: hosts.5,v 1.14 2021/03/12 10:00:32 uwe Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)hosts.5 8.2 (Berkeley) 12/11/93 31.\" 32.Dd November 17, 2000 33.Dt HOSTS 5 34.Os 35.Sh NAME 36.Nm hosts 37.Nd host name data base 38.Sh DESCRIPTION 39The 40.Nm hosts 41file contains information regarding the known hosts on the network. 42It can be used in conjunction with the DNS, and the 43.Tn NIS 44maps 45.Sq hosts.byaddr , 46and 47.Sq hosts.byname , 48as controlled by 49.Xr nsswitch.conf 5 . 50.Pp 51For each host a single line should be present 52with the following information: 53.Dl address hostname [alias ...] 54.Pp 55These are: 56.Bl -tag -width hostname -compact -offset indent 57.It Em address 58Internet address 59.It Em hostname 60Official host name 61.It Em alias 62Alias host name 63.El 64.Pp 65Items are separated by any number of blanks and/or 66tab characters. A hash sign 67.Pq Dq \&# 68indicates the beginning of 69a comment; characters up to the end of the line are 70not interpreted by routines which search the file. 71.Pp 72When using the name server 73.Xr named 8 , 74or 75.Xr ypserv 8 , 76this file provides a backup when the name server 77is not running. 78For the name server, it is suggested that only a few addresses 79be included in this file. 80These include address for the local interfaces that 81.Xr ifconfig 8 82needs at boot time and a few machines on the local network. 83.Pp 84As network addresses, both IPv4 and IPv6 addresses are allowed. 85IPv4 addresses are specified in the conventional dot 86.Pq Dq \&. 87notation using the 88.Xr inet_pton 3 89routine 90from the Internet address manipulation library, 91.Xr inet 3 . 92IPv6 addresses are specified in the standard hex-and-colon notation. 93Host names may contain any printable 94character other than a field delimiter, newline, 95or comment character. 96.Sh FILES 97.Bl -tag -width /etc/hosts -compact 98.It Pa /etc/hosts 99The 100.Nm hosts 101file resides in 102.Pa /etc . 103.El 104.Sh SEE ALSO 105.Xr gethostbyname 3 , 106.Xr nsswitch.conf 5 , 107.Xr ifconfig 8 , 108.Xr named 8 109.Rs 110.%T "Name Server Operations Guide for BIND" 111.Re 112.Sh HISTORY 113The 114.Nm 115file format appeared in 116.Bx 4.2 . 117