1.\" $NetBSD: hosts.5,v 1.7 2000/06/14 03:57:23 itojun 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. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)hosts.5 8.2 (Berkeley) 12/11/93 35.\" 36.Dd January 16, 1999 37.Dt HOSTS 5 38.Os 39.Sh NAME 40.Nm hosts 41.Nd host name data base 42.Sh DESCRIPTION 43The 44.Nm hosts 45file contains information regarding 46It can be used in conjunction with the DNS, and the 47.Tn NIS 48maps 49.Sq hosts.byaddr , 50and 51.Sq hosts.byname , 52as controlled by 53.Xr nsswitch.conf 5 . 54.Pp 55the known hosts on the network. 56For each host a single line should be present 57with the following information: 58.Bd -unfilled -offset indent 59Internet address 60Official host name 61Aliases 62.Ed 63.Pp 64Items are separated by any number of blanks and/or 65tab characters. A ``#'' indicates the beginning of 66a comment; characters up to the end of the line are 67not interpreted by routines which search the file. 68.Pp 69When using the name server 70.Xr named 8 , 71or 72.Xr ypserv 8 , 73this file provides a backup when the name server 74is not running. 75For the name server, it is suggested that only a few addresses 76be included in this file. 77These include address for the local interfaces that 78.Xr ifconfig 8 79needs at boot time and a few machines on the local network. 80.Pp 81This file may be created from the official host 82data base maintained at the Network Information Control 83Center 84.Pq Tn NIC , 85though local changes may be required 86to bring it up to date regarding unofficial aliases 87and/or unknown hosts. As the data base maintained at 88.Tn NIC 89is incomplete, use of the name server is recommended for 90sites on the 91.Tn DARPA 92Internet. 93.Pp 94As network addresses, both IPv4 and IPv6 addresses are allowed. 95IPv4 addresses are specified in the conventional 96``.'' (dot) notation using the 97.Xr inet_pton 3 98routine 99from the Internet address manipulation library, 100.Xr inet 3 . 101IPv6 addresses are specified in the standard hex-and-colon notation. 102Host names may contain any printable 103character other than a field delimiter, newline, 104or comment character. 105.Sh FILES 106.Bl -tag -width /etc/hosts -compact 107.It Pa /etc/hosts 108The 109.Nm hosts 110file resides in 111.Pa /etc . 112.El 113.Sh SEE ALSO 114.Xr gethostbyname 3 , 115.Xr nsswitch.conf 5 , 116.Xr ifconfig 8 , 117.Xr named 8 118.Rs 119.%T "Name Server Operations Guide for BIND" 120.Re 121.Sh HISTORY 122The 123.Nm 124file format appeared in 125.Bx 4.2 . 126