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 trim, multi, nospoof, spoof, and reorder.   These
       keywords are described below.

       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_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 3.53 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)