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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 keywords
       recognized are trim, multi, nospoof, spoof, and  reorder.   These  key-
       words are described below.
       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  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 host-
              name  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 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 secu-
              rity 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  warnings  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 per-
              formed.  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_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 com-
              mand.
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  implementa-
       tion.    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.
SEE ALSO
       gethostbyname(3), hostname(7), named(8), resolv+(8)
COLOPHON
       This  page  is  part of release 3.53 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)