host.conf

host.conf(5) File Formats Manual 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 configura
   tion 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(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 commas.  Valid methods are bind, hosts, and nis.

   RESOLV_SERV_ORDER
          Overrides the order command.

   Since glibc 2.0.7, and up through glibc 2.24, 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:  af
          ter  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 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), hostname(7), named(8)

Linux man-pages 6.9.1 2024-05-02 host.conf(5)