1.\" $OpenBSD: hosts.5,v 1.18 2008/01/29 10:03:44 jmc Exp $ 2.\" $NetBSD: hosts.5,v 1.4 1994/11/30 19:31:20 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)hosts.5 8.2 (Berkeley) 12/11/93 32.\" 33.Dd $Mdocdate: January 29 2008 $ 34.Dt HOSTS 5 35.Os 36.Sh NAME 37.Nm hosts 38.Nd host name database 39.Sh DESCRIPTION 40The 41.Nm 42file contains information regarding the known hosts on the network. 43For each host, a single line should be present with the following information: 44.Bd -unfilled -offset indent 45Internet address 46Official host name 47Aliases 48.Ed 49.Pp 50Items are separated by any number of blanks and/or tab characters. 51A 52.Ql # 53indicates the beginning of a comment; characters up to the end of the line 54are not interpreted by routines which search the file. 55.Pp 56The system configuration file 57.Xr resolv.conf 5 58controls where host name information will be searched for. 59The mechanism provided permits the administrator to describe the 60databases to search; the databases currently known include 61.Xr yp 8 , 62DNS 63and the 64.Nm hosts 65database. 66.Pp 67When using the name server 68.Xr named 8 , 69this file provides a backup when the name server is not running. 70For the name server, it is suggested that only a few addresses 71be included in this file. 72These include addresses for the local interfaces that 73.Xr ifconfig 8 74needs at boot time and a few machines on the local network. 75.Pp 76This file may be created from the official host database maintained at the 77Network Information Control Center 78.Pq Tn NIC , 79though local changes may be required to bring it up to date regarding 80unofficial aliases and/or unknown hosts. 81As the database maintained at 82.Tn NIC 83is incomplete, use of the name server is recommended for sites on the 84.Tn DARPA 85Internet. 86.Pp 87Internet addresses are specified using either 88dot notation (IPv4) 89or colon separated notation (IPv6). 90Further information on network addressing is contained in 91.Xr inet 3 . 92Host names may contain any printable character other than a field delimiter, 93newline, or comment character. 94.Sh FILES 95.Bl -tag -width /etc/hosts -compact 96.It Pa /etc/hosts 97.El 98.Sh SEE ALSO 99.Xr getaddrinfo 3 , 100.Xr gethostbyname 3 , 101.Xr getnameinfo 3 , 102.Xr inet 3 , 103.Xr resolv.conf 5 , 104.Xr ifconfig 8 , 105.Xr named 8 106.Rs 107.%T "Name Server Operations Guide for BIND" 108.Re 109.Sh HISTORY 110The 111.Nm 112file format appeared in 113.Bx 4.2 . 114.Sh BUGS 115A name server should be used instead of a static file. 116.Pp 117Lines in 118.Pa /etc/hosts 119are limited to 120.Dv BUFSIZ 121characters 122.Pq currently 1024 . 123Longer lines will be ignored. 124