1.\" $OpenBSD: hosts.5,v 1.11 2000/11/20 08:00:03 deraadt 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. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)hosts.5 8.2 (Berkeley) 12/11/93 36.\" 37.Dd December 11, 1993 38.Dt HOSTS 5 39.Os 40.Sh NAME 41.Nm hosts 42.Nd host name database 43.Sh DESCRIPTION 44The 45.Nm 46file contains information regarding the known hosts on the network. 47For each host, a single line should be present with the following information: 48.Bd -unfilled -offset indent 49Internet address 50Official host name 51Aliases 52.Ed 53.Pp 54Items are separated by any number of blanks and/or tab characters. 55A 56.Ql # 57indicates the beginning of a comment; characters up to the end of the line 58are not interpreted by routines which search the file. 59.Pp 60The system configuration file 61.Xr resolv.conf 5 62controls where host name information will be searched for. 63The mechanism provided permits the administrator to describe the 64databases to search; the databases currently known include 65.Xr yp 8 , 66DNS 67and the 68.Xr hosts 5 69database. 70.Pp 71When using the name server 72.Xr named 8 , 73this file provides a backup when the name server is not running. 74For the name server, it is suggested that only a few addresses 75be included in this file. 76These include addresses for the local interfaces that 77.Xr ifconfig 8 78needs at boot time and a few machines on the local network. 79.Pp 80This file may be created from the official host database maintained at the 81Network Information Control Center 82.Pq Tn NIC , 83though local changes may be required to bring it up to date regarding 84unofficial aliases and/or unknown hosts. 85As the database maintained at 86.Tn NIC 87is incomplete, use of the name server is recommended for sites on the 88.Tn DARPA 89Internet. 90.Pp 91Network addresses are specified in the conventional Internet 92.Dq \&. 93(dot) notation using the 94.Xr inet_addr 3 95routine from the Internet address manipulation library, 96.Xr inet 3 . 97Host names may contain any printable character other than a field delimiter, 98newline, or comment character. 99.Sh FILES 100.Bl -tag -width /etc/hosts -compact 101.It Pa /etc/hosts 102.El 103.Sh SEE ALSO 104.Xr gethostbyname 3 , 105.Xr getaddrinfo 3 , 106.Xr getnameinfo 3 , 107.Xr resolv.conf 5 , 108.Xr ifconfig 8 , 109.Xr named 8 110.Rs 111.%T "Name Server Operations Guide for BIND" 112.Re 113.Sh BUGS 114A name server should be used instead of a static file. 115.Pp 116Lines in 117.Pa /etc/hosts 118are limited to 119.Dv BUFSIZE 120characters (currently 1024). 121Longer lines will be ignored. 122.Sh HISTORY 123The 124.Nm 125file format appeared in 126.Bx 4.2 . 127