.\"	$OpenBSD: hosts.5,v 1.18 2008/01/29 10:03:44 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.
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.\"     @(#)hosts.5	8.2 (Berkeley) 12/11/93
.\"
.Dd $Mdocdate: January 29 2008 $
.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 the name server
.Xr named 8 ,
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
This file may be created from the official host database maintained at the
Network Information Control Center
.Pq Tn NIC ,
though local changes may be required to bring it up to date regarding
unofficial aliases and/or unknown hosts.
As the database maintained at
.Tn NIC
is incomplete, use of the name server is recommended for sites on the
.Tn DARPA
Internet.
.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 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 3 ,
.Xr resolv.conf 5 ,
.Xr ifconfig 8 ,
.Xr named 8
.Rs
.%T "Name Server Operations Guide for BIND"
.Re
.Sh HISTORY
The
.Nm
file format appeared in
.Bx 4.2 .
.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.