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NAME | DESCRIPTION | ENVIRONMENT | FILES | NOTES | SEE ALSO | COLOPHON |
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HOST.CONF(5) Linux System Administration HOST.CONF(5)
host.conf - resolver configuration file
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
(':'), semicolons (';') or commas (','), 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 and off. If set to on, the resolver
library will return all valid addresses for a host that
appears in the /etc/hosts file, instead of only the first.
This is off by default, as it may cause a substantial
performance loss at sites with large hosts files.
reorder
Valid values are on and off. If set to on, 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 is off.
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 (':'), semicolons
(';') or commas (','), 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 (':'), semicolons
(';') or commas (','), with the leading dot, which will
replace the list of domains that should be trimmed. Overrides
the trim command.
/etc/host.conf
Resolver configuration file
/etc/resolv.conf
Resolver configuration file
/etc/hosts
Local hosts database
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, and nis.
RESOLV_SERV_ORDER
Overrides the order command.
Since glibc 2.0.7, the following keywords and environment variable
have been recognized but never implemented:
nospoof
Valid values are on and off. If set to on, 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 is
off.
spoofalert
Valid values are on and off. If this option is set to on and
the nospoof option is also set, the resolver library will log
a warning of the error via the syslog facility. The default
value is off.
spoof Valid values are off, nowarn, and warn. If this option is set
to off, spoofed addresses are permitted and no warnings will
be emitted via the syslog facility. If this option is set to
warn, 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 to
nowarn, 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 to nowarn.
RESOLV_SPOOF_CHECK
Overrides the nospoof, spoofalert, and spoof commands in the
same way as the spoof command is parsed. Valid values are
off, nowarn, and warn.
gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5),
hostname(7), named(8)
This page is part of release 4.15 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/.
Linux 2017-09-15 HOST.CONF(5)
Pages that refer to this page: gethostbyname(3), hosts(5), resolv.conf(5)
Copyright and license for this manual page
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