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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 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 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_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 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 3.54 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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