1.\" $OpenBSD: hosts.5,v 1.27 2023/11/25 08:14:43 florian 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: November 25 2023 $ 34.Dt HOSTS 5 35.Os 36.Sh NAME 37.Nm hosts 38.Nd host and network name database 39.Sh DESCRIPTION 40The 41.Nm 42file associates names and IP addresses. 43Each line has the following format: 44.Bd -unfilled -offset indent 45Internet address 46Host or network 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 61DNS 62and the 63.Nm hosts 64database. 65.Pp 66When using a name server, 67this file provides a backup when the name server is not running. 68For the name server, it is suggested that only a few addresses 69be included in this file. 70These include addresses for the local interfaces that 71.Xr ifconfig 8 72needs at boot time and a few machines on the local network. 73.Pp 74Internet addresses are specified using either 75dot notation (IPv4) or colon separated notation (IPv6) as described in 76.Xr inet_pton 3 . 77Host names may contain any printable character other than a field delimiter, 78newline, or comment character. 79.Pp 80The host "localhost" and all names underneath the localhost domain will 81always resolve to the loopback addresses 127.0.0.1 or ::1. 82.Sh FILES 83.Bl -tag -width /etc/hosts -compact 84.It Pa /etc/hosts 85.El 86.Sh SEE ALSO 87.Xr getaddrinfo 3 , 88.Xr gethostbyname 3 , 89.Xr getnameinfo 3 , 90.Xr inet_pton 3 , 91.Xr resolv.conf 5 , 92.Xr ifconfig 8 , 93.Xr nsd 8 , 94.Xr unbound 8 95.Sh HISTORY 96The 97.Nm 98file format appeared in 99.Bx 4.2 . 100.Pp 101An official host database used to be maintained at 102the Network Information Control Center (NIC). 103.Pp 104Up to 105.Ox 6.3 , 106a separate file 107.Pa /etc/networks 108could be used to store network names. 109.Sh BUGS 110A name server should be used instead of a static file. 111.Pp 112Lines in 113.Pa /etc/hosts 114are limited to 115.Dv BUFSIZ 116characters 117.Pq currently 1024 . 118Longer lines will be ignored. 119