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Document that "localhost" only resolves to the loopback addresses.
prodding pb
OK phessler, sthen
Input & OK jmc

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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.