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  (':'),  semi-
	      colons  (';')  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(5) 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 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 gethostbyname(3) is performed.  Reordering is done for all lookup methods.  The
	      default value is off.

ENVIRONMENT

       The following environment variables 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_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.

   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 com-
	      mas.  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 security
	      of rlogin and rsh.  It works as follows: after performing a host address lookup, the resolver library will perform a hostname lookup
	      for that address.  If the two hostnames do not match, the query fails.  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 warn-
	      ing 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, 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), hostname(7), named(8)

COLOPHON

       This  page is part of release 4.15 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								    2017-09-15							      HOST.CONF(5)