NAME | DESCRIPTION | ENVIRONMENT | FILES | NOTES | SEE ALSO | COLOPHON
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 keywords recognized
are order, trim, multi, nospoof, spoof, and reorder. These keywords are
described below.
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.
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 resolv+
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 file. Care should be taken to ensure
that the first hostname for each entry in the hosts file is fully
qualified or non-qualified, as appropriate for the local installation.)
multi Valid values are on and off. If set to on, the resolv+ 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.
nospoof
Valid values are on and off. If set to on, the resolv+ 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,
resolv+ will perform a hostname lookup for that address. If the two
hostnames do not match, the query will fail. 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, resolv+ 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, resolv+ 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 resolv+ 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.
reorder
Valid values are on and off. If set to on, resolv+ 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.
There are six environment variables that 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_SERV_ORDER
Overrides the order command.
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.
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.
gethostbyname(3), hostname(7), named(8), resolv+(8)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2003-08-23 HOST.CONF(5)