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 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, 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 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, 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 4.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                            2015-07-23                     HOST.CONF(5)