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 following
       keywords are recognized:

       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	 resolver  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 resolver 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.

       reorder
	      Valid values are on and off.  If set to on, the resolver library
	      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	 meth-
	      ods.  The default value is off.

ENVIRONMENT
       The following environment variables can be used to allow users to over-
       ride 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_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.

   Historical
       The nsswitch.conf(5) file is the modern way of controlling the order of
       host lookups.

       In glibc 2.4 and earlier, the following keyword is recognized:

       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.

       RESOLV_SERV_ORDER
	      Overrides the order command.

       Since glibc 2.0.7, the following keywords and environment variable have
       been recognized but never implemented:

       nospoof
	      Valid values are on and off.  If set to on, the resolver 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, the resolver library will perform  a	 host-
	      name  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, the resolver library 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,
	      the resolver library 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  resolver
	      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.

       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.

SEE ALSO
       gethostbyname(3),  hosts(5),  nsswitch.conf(5),	resolv.conf(5),	 host-
       name(7), named(8)

COLOPHON
       This page is part of release 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2015-07-23			  HOST.CONF(5)