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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 do-
              main 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 de-
              fault, 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  in-
              stead 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  RE-
       SOLV_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  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 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),  host-
       name(7), named(8)

COLOPHON
       This page is part of release 5.05 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                             2019-03-06                      HOST.CONF(5)

NAME | DESCRIPTION | ENVIRONMENT | FILES | NOTES | SEE ALSO | COLOPHON