Section (5) host.conf
Name
host.conf — resolver configuration file
DESCRIPTION
The file /etc/host.conf
contains configuration information specific to the resolver
library. It should contain one configuration keyword per
line, followed by appropriate configuration information. The
following keywords are recognized:
trim
-
This keyword may be listed more than once. Each time it should be followed by a list of domains, separated by colons (_zsingle_quotesz_:_zsingle_quotesz_), semicolons (_zsingle_quotesz_;_zsingle_quotesz_) or commas (_zsingle_quotesz_,_zsingle_quotesz_), with the leading dot. When set, the resolver library will automatically trim the given domain name from the end of any hostname resolved via DNS. This is intended for use with local hosts and domains. (Related note:
trim
will not affect hostnames gathered via NIS or the hosts(5) file. Care should be taken to ensure that the first hostname for each entry in the hosts file is fully qualified or unqualified, as appropriate for the local installation.) multi
-
Valid values are
on
andoff
. If set toon
, the resolver library will return all valid addresses for a host that appears in the/etc/hosts
file, instead of only the first. This isoff
by default, as it may cause a substantial performance loss at sites with large hosts files. reorder
-
Valid values are
on
andoff
. If set toon
, the resolver library will attempt to reorder host addresses so that local addresses (i.e., on the same subnet) are listed first when a gethostbyname(3) is performed. Reordering is done for all lookup methods. The default value isoff
.
ENVIRONMENT
The following environment variables can be used to allow
users to override the behavior which is configured in
/etc/host.conf
:
RESOLV_HOST_CONF
-
If set, this variable points to a file that should be read instead of
/etc/host.conf
. RESOLV_MULTI
-
Overrides the
multi
command. RESOLV_REORDER
-
Overrides the
reorder
command. RESOLV_ADD_TRIM_DOMAINS
-
A list of domains, separated by colons (_zsingle_quotesz_:_zsingle_quotesz_), semicolons (_zsingle_quotesz_;_zsingle_quotesz_) or commas (_zsingle_quotesz_,_zsingle_quotesz_), with the leading dot, which will be added to the list of domains that should be trimmed.
RESOLV_OVERRIDE_TRIM_DOMAINS
-
A list of domains, separated by colons (_zsingle_quotesz_:_zsingle_quotesz_), semicolons (_zsingle_quotesz_;_zsingle_quotesz_) or commas (_zsingle_quotesz_,_zsingle_quotesz_), with the leading dot, which will replace the list of domains that should be trimmed. Overrides the
trim
command.
FILES
/etc/host.conf
-
Resolver configuration file
/etc/resolv.conf
-
Resolver configuration file
/etc/hosts
-
Local hosts database
NOTES
The following differences exist compared to the original
implementation. A new command spoof
and a new environment variable
RESOLV_SPOOF_CHECK
can take
arguments like off
, nowarn
, and warn
. Line comments can appear anywhere and
not only at the beginning of a line.
Historical
The nsswitch.conf(5) file is the modern way of controlling the order of host lookups.
In glibc 2.4 and earlier, the following keyword is recognized:
order
-
This keyword specifies how host lookups are to be performed. It should be followed by one or more lookup methods, separated by commas. Valid methods are
bind
,hosts
, andnis
. RESOLV_SERV_ORDER
-
Overrides the
order
command.
Since glibc 2.0.7, and up through glibc 2.24, the following keywords and environment variable have been recognized but never implemented:
nospoof
-
Valid values are
on
andoff
. If set toon
, the resolver library will attempt to prevent hostname spoofing to enhance the security of rlogin and rsh. It works as follows: after performing a host address lookup, the resolver library will perform a hostname lookup for that address. If the two hostnames do not match, the query fails. The default value isoff
. spoofalert
-
Valid values are
on
andoff
. If this option is set toon
and thenospoof
option is also set, the resolver library will log a warning of the error via the syslog facility. The default value isoff
. spoof
-
Valid values are
off
,nowarn
, andwarn
. If this option is set tooff
, spoofed addresses are permitted and no warnings will be emitted via the syslog facility. If this option is set towarn
, the resolver library will attempt to prevent hostname spoofing to enhance the security and log a warning of the error via the syslog facility. If this option is set tonowarn
, the resolver library will attempt to prevent hostname spoofing to enhance the security but not emit warnings via the syslog facility. Setting this option to anything else is equal to setting it tonowarn
. RESOLV_SPOOF_CHECK
-
Overrides the
nospoof
,spoofalert
, andspoof
commands in the same way as thespoof
command is parsed. Valid values areoff
,nowarn
, andwarn
.
COLOPHON
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (c) 1997 Martin Schulze (joeyinfodrom.north.de) Much of the text is copied from the manpage of resolv+(8). %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License_zsingle_quotesz_s references to object code and executables are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END 2003-08-23 Martin Schulze <joeyinfodrom.org> Updated according to glibc 2.3.2 |