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 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 quali-
	      fied or non-qualified, as appropriate for the  local  installa-
	      tion.)

       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 gethostby-
	      name(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  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), resolv+(8), named(8)



Debian GNU/Linux		  2003-08-23			 HOST.CONF(5)