169 lines
5.2 KiB
Groff
169 lines
5.2 KiB
Groff
.\" Copyright (c) 1987 The Regents of the University of California.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms are permitted
|
|
.\" provided that the above copyright notice and this paragraph are
|
|
.\" duplicated in all such forms and that any documentation,
|
|
.\" advertising materials, and other materials related to such
|
|
.\" distribution and use acknowledge that the software was developed
|
|
.\" by the University of California, Berkeley. The name of the
|
|
.\" University may not be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
|
|
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
|
|
.\"
|
|
.\" @(#)hostname.7 6.4 (Berkeley) 1/16/90
|
|
.\"
|
|
.Dd February 16, 1994
|
|
.Dt HOSTNAME @DESC_EXT_U@
|
|
.Os BSD 4
|
|
.Sh NAME
|
|
.Nm hostname
|
|
.Nd host name resolution description
|
|
.Sh DESCRIPTION
|
|
Hostnames are domains. A domain is a hierarchical, dot-separated list
|
|
of subdomains. For example, the machine
|
|
.Dq Li monet ,
|
|
in the
|
|
.Dq Li Berkeley
|
|
subdomain of the
|
|
.Dq Li EDU
|
|
subdomain of the Internet Domain Name System would be represented as
|
|
.Pp
|
|
.Dl monet.Berkeley.EDU
|
|
.Pp
|
|
(with no trailing dot).
|
|
.Pp
|
|
Hostnames are often used with network client and server programs,
|
|
which must generally translate the name to an address for use.
|
|
(This task is usually performed by the library routine
|
|
.Xr gethostbyname @LIB_NETWORK_EXT@ . )
|
|
The default method for resolving hostnames by the Internet name resolver is
|
|
to follow RFC 1535's security recommendations. Actions can be taken
|
|
by the administrator to override these recommendations and to have the
|
|
resolver behave the same as earlier, non-RFC 1535
|
|
resolvers.
|
|
.Pp
|
|
The default method (using RFC 1535 guidelines) follows:
|
|
.Pp
|
|
If the name consists of a single component, i.e. contains no dot, and if the
|
|
environment variable
|
|
.Dq Ev HOSTALIASES
|
|
is set to the name of a file,
|
|
that file is searched for a string matching the input hostname. The file
|
|
should consist of lines made up of two strings separated by white-space, the
|
|
first of which is the hostname alias, and the second of which is the complete
|
|
hostname to be substituted for that alias. If a case-insensitive match is
|
|
found between the hostname to be resolved and the first field of a line in
|
|
the file, the substituted name is looked up with no further processing.
|
|
.Pp
|
|
If there is at least one dot in the name, then the name is first tried
|
|
.Dq as-is .
|
|
The number of dots to cause this action is configurable by setting the
|
|
threshold using the
|
|
.Dq Li ndots
|
|
option in
|
|
.Pa /etc/resolv.conf
|
|
(default: 1). If the name ends with a dot, the trailing dot is
|
|
removed, and the remaining name is looked up (regardless of the setting of
|
|
the
|
|
.Li ndots
|
|
option), without further processing.
|
|
.Pp
|
|
If the input name does not end with a trailing dot, it is looked up by
|
|
searching through a list of domains until a match is found. If neither the
|
|
search option in the
|
|
.Pa /etc/resolv.conf
|
|
file or the
|
|
.Dq Ev LOCALDOMAIN
|
|
environment variable is used, then the
|
|
search list of domains contains only the full domain specified by the
|
|
.Li domain
|
|
option (in
|
|
.Pa /etc/resolv.conf )
|
|
or the domain used in the local hostname (see
|
|
.Xr hostname @CMD_EXT@
|
|
and
|
|
.Xr resolver @FORMAT_EXT@ ) .
|
|
For example, if the
|
|
.Dq Li domain
|
|
option is set to
|
|
.Li CS.Berkeley.EDU ,
|
|
then only
|
|
.Li CS.Berkeley.EDU
|
|
will be in the search list, and this will be the only
|
|
domain appended to the partial hostname. For example, if
|
|
.Dq Li lithium
|
|
is the name to be resolved, this would make
|
|
.Li lithium.CS.Berkeley.EDU
|
|
the only name to be tried using the search list.
|
|
.Pp
|
|
If the
|
|
.Li search
|
|
option is used in
|
|
.Pa /etc/resolv.conf
|
|
or the environment variable
|
|
.Dq Ev LOCALDOMAIN
|
|
is set by the user, then
|
|
the search list will include what is set by these methods. For
|
|
example, if the
|
|
.Dq Li search
|
|
option contained
|
|
.Pp
|
|
.Dl CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU
|
|
.Pp
|
|
then the partial hostname (e.g.,
|
|
.Dq Li lithium )
|
|
will be tried with
|
|
.Em each
|
|
domain name appended (in the same order specified); the resulting hostnames
|
|
that would be tried are:
|
|
.Bd -literal -offset indent
|
|
lithium.CS.Berkeley.EDU
|
|
lithium.CChem.Berkeley.EDU
|
|
lithium.Berkeley.EDU
|
|
.Ed
|
|
.Pp
|
|
The environment variable
|
|
.Dq Ev LOCALDOMAIN
|
|
overrides the
|
|
.Dq Li search
|
|
and
|
|
.Dq Li domain
|
|
options, and if both
|
|
.Li search
|
|
and
|
|
.Li domain
|
|
options are present in the resolver configuration file, then only the
|
|
.Em last
|
|
one listed is used (see
|
|
.Xr resolver @FORMAT_EXT@ ) .
|
|
.Pp
|
|
If the name was not previously tried
|
|
.Dq as-is
|
|
(i.e., it fell below the
|
|
.Dq Li ndots
|
|
threshold or did not contain a dot), then the name as
|
|
originally provided is attempted.
|
|
.Sh ENVIRONMENT
|
|
.Bl -tag -width "/etc/resolv.conf "
|
|
.It Ev LOCALDOMAIN
|
|
Affects domains appended to partial hostnames.
|
|
.It Ev HOSTALIASES
|
|
Name of file containing
|
|
.Pq Ar host alias , full hostname
|
|
pairs.
|
|
.El
|
|
.Sh FILES
|
|
.Bl -tag -width "/etc/resolv.conf " -compact
|
|
.It Pa /etc/resolv.conf
|
|
See
|
|
.Xr resolve @FORMAT_EXT@ .
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr gethostbyname @LIB_NETWORK_EXT@ ,
|
|
.Xr resolver @FORMAT_EXT@ ,
|
|
.Xr mailaddr @DESC_EXT@ ,
|
|
.Xr @INDOT@named @SYS_OPS_EXT@ .
|