host.conf

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



NAME
       host.conf - resolver configuration file

DESCRIPTION
       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
       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
       /etc/host.conf
              Resolver configuration file

       /etc/resolv.conf
              Resolver configuration file

       /etc/hosts
              Local hosts database

NOTES
       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
       gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5),
       hostname(7), named(8)

COLOPHON
       This page is part of release 5.00 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                             2019-03-06                      HOST.CONF(5)