.\"	$OpenBSD: hosts.5,v 1.27 2023/11/25 08:14:43 florian 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.
.\"
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.\" 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
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.\" 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: November 25 2023 $
.Dt HOSTS 5
.Os
.Sh NAME
.Nm hosts
.Nd host and network name database
.Sh DESCRIPTION
The
.Nm
file associates names and IP addresses.
Each line has the following format:
.Bd -unfilled -offset indent
Internet address
Host or network 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
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) as described in
.Xr inet_pton 3 .
Host names may contain any printable character other than a field delimiter,
newline, or comment character.
.Pp
The host "localhost" and all names underneath the localhost domain will
always resolve to the loopback addresses 127.0.0.1 or ::1.
.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_pton 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 (NIC).
.Pp
Up to
.Ox 6.3 ,
a separate file
.Pa /etc/networks
could be used to store network names.
.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.