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)
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