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.\" $OpenBSD: hosts.5,v 1.22 2014/08/23 07:25:54 jmc Exp $
.\" $NetBSD: hosts.5,v 1.4 1994/11/30 19:31:20 jtc Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)hosts.5 8.2 (Berkeley) 12/11/93
.\"
.Dd $Mdocdate: August 23 2014 $
.Dt HOSTS 5
.Os
.Sh NAME
.Nm hosts
.Nd host name database
.Sh DESCRIPTION
The
.Nm
file contains information regarding the known hosts on the network.
For each host, a single line should be present with the following information:
.Bd -unfilled -offset indent
Internet address
Official host name
Aliases
.Ed
.Pp
Items are separated by any number of blanks and/or tab characters.
A
.Ql #
indicates the beginning of a comment; characters up to the end of the line
are not interpreted by routines which search the file.
.Pp
The system configuration file
.Xr resolv.conf 5
controls where host name information will be searched for.
The mechanism provided permits the administrator to describe the
databases to search; the databases currently known include
.Xr yp 8 ,
DNS
and the
.Nm hosts
database.
.Pp
When using a name server
this file provides a backup when the name server is not running.
For the name server, it is suggested that only a few addresses
be included in this file.
These include addresses for the local interfaces that
.Xr ifconfig 8
needs at boot time and a few machines on the local network.
.Pp
Internet addresses are specified using either
dot notation (IPv4)
or colon separated notation (IPv6).
Further information on network addressing is contained in
.Xr inet_addr 3 .
Host names may contain any printable character other than a field delimiter,
newline, or comment character.
.Sh FILES
.Bl -tag -width /etc/hosts -compact
.It Pa /etc/hosts
.El
.Sh SEE ALSO
.Xr getaddrinfo 3 ,
.Xr gethostbyname 3 ,
.Xr getnameinfo 3 ,
.Xr inet_addr 3 ,
.Xr resolv.conf 5 ,
.Xr ifconfig 8 ,
.Xr nsd 8 ,
.Xr unbound 8
.Sh HISTORY
The
.Nm
file format appeared in
.Bx 4.2 .
.Pp
An official host database used to be maintained at
the Network Information Control Center
.Pq Tn NIC .
.Sh BUGS
A name server should be used instead of a static file.
.Pp
Lines in
.Pa /etc/hosts
are limited to
.Dv BUFSIZ
characters
.Pq currently 1024 .
Longer lines will be ignored.
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