.\"	$OpenBSD: hosts.5,v 1.9 2000/03/19 19:25:29 aaron 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
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.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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 December 11, 1993
.Dt HOSTS 5
.Os
.Sh NAME
.Nm hosts
.Nd host name data base
.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 5 ,
DNS
and the
.Xr hosts 5
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
data base 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 data base maintained at
.Tn NIC
is incomplete, use of the name server is recommended for
sites on the
.Tn DARPA
Internet.
.Pp
Network addresses are specified in the conventional Internet
.Dq \&.
(dot) notation using the
.Xr inet_addr 3
routine
from the Internet address manipulation library,
.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 gethostbyname 3 ,
.Xr getaddrinfo 3 ,
.Xr getnameinfo 3 ,
.Xr resolv.conf 5 ,
.Xr ifconfig 8 ,
.Xr named 8
.Rs
.%T "Name Server Operations Guide for BIND"
.Re
.Sh BUGS
A name server should be used instead of a static file.
.Pp
Lines in
.Pa /etc/hosts
are limited to
.Dv BUFSIZE
characters (currently 1024).
Longer lines will be ignored.
.Sh HISTORY
The
.Nm
file format appeared in
.Bx 4.2 .