host.conf(5) - Linux manual page (original) (raw)
host.conf(5) File Formats Manual host.conf(5)
NAME top
host.conf - resolver configuration fileDESCRIPTION top
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)](../man5/hosts.5.html) 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)](../man3/gethostbyname.3.html) is performed. Reordering is done
for all lookup methods. The default value is _off_.ENVIRONMENT top
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.FILES top
_/etc/host.conf_
Resolver configuration file
_/etc/resolv.conf_
Resolver configuration file
_/etc/hosts_
Local hosts databaseNOTES top
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, and up through glibc 2.24, 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_.SEE ALSO top
[gethostbyname(3)](../man3/gethostbyname.3.html), [hosts(5)](../man5/hosts.5.html), [nsswitch.conf(5)](../man5/nsswitch.conf.5.html), [resolv.conf(5)](../man5/resolv.conf.5.html),
[hostname(7)](../man7/hostname.7.html), **named**(8)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-05-02 host.conf(5)
Pages that refer to this page:gethostbyname(3), hosts(5), resolv.conf(5)