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 com-
	      mas.  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  (':'),  semi-
	      colons  (';')  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 emit-
	      ted via the syslog facility.  If this option is set to warn, resolv+ will attempt to prevent hostname spoofing to enhance the  secu-
	      rity  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 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  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 3.25 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)