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NAME | DESCRIPTION | ENVIRONMENT | FILES | NOTES | SEE ALSO | COLOPHON |
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host.conf(5) File Formats Manual 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, 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.
gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5),
hostname(7), named(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-05-02 host.conf(5)
Pages that refer to this page: gethostbyname(3), hosts(5), resolv.conf(5)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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