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Linux 2.6 - man page for host.conf (linux section 5)

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  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 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 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 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 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 behav-
       ior 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	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 3.55 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)


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