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:
trimThis 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.)
multiValid 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.
reorderValid 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:
If set, this variable points to a file that should be read instead of
/etc/host.conf.
Overrides the multi command.
Overrides the reorder command.
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.
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.confResolver configuration file
/etc/resolv.confResolver configuration file
/etc/hostsLocal 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.
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:
orderThis 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.
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:
nospoofValid 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.
spoofalertValid 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.
spoofValid 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.
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)