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 con-
       figuration keyword per line, followed by appropriate configuration information.  The keywords recognized are order, trim,
       multi, nospoof, spoof, and reorder.  These keywords are described below.

       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.

       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 resolv+ library will automat-
              ically 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  unquali-
              fied, as appropriate for the local installation.)

       multi  Valid  values  are  on and off.  If set to on, the resolv+ 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.

       nospoof
              Valid  values  are  on  and  off.   If set to on, the resolv+ 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, resolv+ 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, resolv+ 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 warn-
              ings will be emitted via the syslog facility.  If this option is set to warn,  resolv+  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 resolv+ 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.

       reorder
              Valid values are on and off.  If set to on, resolv+ 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
       There  are  six  environment  variables  that  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_SERV_ORDER
              Overrides the order command.

       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.

       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 vari-
       able 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.

SEE ALSO
       gethostbyname(3), hostname(7), named(8), resolv+(8)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2003-08-23                                               HOST.CONF(5)