host.conf(5) — Linux manual page

NAME | DESCRIPTION | ENVIRONMENT | FILES | NOTES | SEE ALSO | COLOPHON

HOST.CONF(5)           Linux System Administration          HOST.CONF(5)

NAME         top

       host.conf - resolver configuration file

DESCRIPTION         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)
              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.

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 database

NOTES         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), hosts(5), nsswitch.conf(5), resolv.conf(5),
       hostname(7), named(8)

COLOPHON         top

       This page is part of release 5.10 of the Linux man-pages project.
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       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2019-03-06                   HOST.CONF(5)

Pages that refer to this page: gethostbyname(3)hosts(5)resolv.conf(5)