Provided by: resolvconf_1.91ubuntu1_all bug


       resolvconf - manage nameserver information


       cat FILE | resolvconf -a IFACE.PROG

       resolvconf -d IFACE.PROG

       resolvconf -u

       resolvconf -i

       resolvconf --list | -l

       resolvconf   --enable-updates   |  --disable-updates  |  --updates-are-enabled  resolvconf

       resolvconf --help | -h


       The resolvconf package comprises a simple database for run-time nameserver information and
       a  simple framework for notifying applications of changes in that information.  Resolvconf
       thus  sets  itself  up  as  the  intermediary  between  programs  that  supply  nameserver
       information and applications that use that information.

       Information  is  added  to or removed from the database using the resolvconf program.  See
       the OPTIONS section below for a discussion of the available options.


       Normally the resolvconf program is run only by network  interface  configuration  programs
       such  as  ifup(8),  ifdown,  NetworkManager(8),  dhclient(8),  and  pppd(8);  and by local
       nameservers such as dnsmasq(8).  These programs obtain nameserver  information  from  some
       source and push it to resolvconf.

       The dhclient program, for example, may receive nameserver addresses and domain search list
       information during  its  negotiation  with  the  DHCP  server;  if  so,  its  hook  script
       /etc/dhcp/dhclient-enter-hooks.d/resolvconf pushes this information to resolvconf.

       The  ifup  program  can  be  used to configure network interfaces according to settings in
       /etc/network/interfaces.  To make ifup push nameserver information to resolvconf  when  it
       configures an interface the administrator must add dns- option lines to the relevant iface
       stanza in  interfaces(5).   The  following  option  names  are  accepted:  dns-nameserver,
       dns-search, and dns-sortlist.

       To  add  a  nameserver IP address, add an option line consisting of dns-nameserver and the
       address.  To add multiple  nameserver  addresses,  include  multiple  such  dns-nameserver


       To add search domain names, add a line beginning with dns-search.


       The  dns-nameservers  option  is  also  accepted  and, unlike dns-nameserver, can be given
       multiple arguments, separated by spaces.

       The dns-domain option is deprecated in favor of dns-search.

       The resulting stanza might look like the following example.

           iface eth0 inet static

       N.B.: On a machine where resolvconf has just been or is about to be  installed  and  which
       previously relied on a static /etc/resolv.conf file,

       •      the nameserver information in that static file, (which is to say the information on
              nameserver,  domain,  search  and  sortlist  lines)  should  be  migrated  to   the
              appropriate iface stanza(s) in /etc/network/interfaces(5) as just described;

       •      options   (which   is   to   say,   any   options  lines)  should  be  migrated  to

   Command line
       The administrator can run resolvconf from the command line to  add  or  delete  nameserver
       information, but this is not normally necessary or advisable.


       Nameserver  information  provided  to  resolvconf  is  stored  for  use  by subscribers to
       resolvconf's notification service.  Subscriber packages that need to know when  nameserver
       information  has  changed  should  install  a  script  in /etc/resolvconf/update.d/ (or in
       /etc/resolvconf/update-libc.d/: see below).  For example, DNS caches  such  as  dnsmasq(8)
       and  pdnsd(8)  subscribe  to the notification service so that they know whither to forward
       queries.  Client hook scripts will find the files containing nameserver information in the
       current directory.

       The most important software package that subscribes to the notification service is the GNU
       C Library resolver(3).  This library is used by many applications  that  need  to  resolve
       domain     names.     When    nameserver    information    is    updated,    the    script
       /etc/resolvconf/update.d/libc generates a new version of the resolver configuration  file,
       /run/resolvconf/resolv.conf,  as  described below.  If the new version of the file differs
       from   the   previously   generated   one    then    the    hook    scripts    found    in
       /etc/resolvconf/update-libc.d/ are executed.

       The  dynamically  generated resolver configuration file always starts with the contents of
       /etc/resolvconf/resolv.conf.d/head     and     ends     with     the      contents      of
       /etc/resolvconf/resolv.conf.d/tail.  Between head and tail the libc script inserts dynamic
       nameserver  information  compiled  from,  first,  information  provided   for   configured
       interfaces;    second,   static   information   from   /etc/resolvconf/resolv.conf.d/base.
       Specifically, it writes:

         1) up to three nameserver lines, ordered according  to  /etc/resolvconf/interface-order,
            possibly   fewer   if   one   of   the  addresses  is  a  loopback  address  and  the
            TRUNCATE_NAMESERVER_LIST_AFTER_LOOPBACK_ADDRESS environment variable is affirmatively
            set, as discussed in the ENVIRONMENT VARIABLES section;

         2) up  to  one  search line containing the combined domain search list from all "domain"
            and "search" input lines, also ordered according to interface-order(5);

         3) all other non-comment input lines.

       To make the resolver use  this  dynamically  generated  resolver  configuration  file  the
       administrator    should   ensure   that   /etc/resolv.conf   is   a   symbolic   link   to
       /run/resolvconf/resolv.conf.  This  link  is  normally  created  on  installation  of  the
       resolvconf  package.  The link is never modified by the resolvconf program itself.  If you
       find that /etc/resolv.conf is not being updated, please check to make sure that  the  link
       is intact.

       The  GNU  C  Library resolver library isn't the only resolver library available.  However,
       any resolver library that reads /etc/resolv.conf (and most of them  do,  in  order  to  be
       compatible) should work fine with resolvconf.

       Subscriber  packages  that  need  to  know  only  when the resolver configuration file has
       changed  should  install  a  script  in  /etc/resolvconf/update-libc.d/  rather  than   in
       /etc/resolvconf/update.d/.   (For  example,  two packages that install update-libc.d/ hook
       scripts are fetchmail and squid.)  This is important for synchronization purposes: scripts
       in  update-libc.d/ are run after resolv.conf has been updated; the same is not necessarily
       true of scripts in update.d/.


       -a IFACE.PROG
              Add or overwrite the record IFACE.PROG then run the update scripts if  updating  is
              enabled.   When  this option is used the information must be provided to resolvconf
              on its standard input in the format of the resolv.conf(5) file.  Each line  in  the
              file must be terminated by a newline.

       -d IFACE.PROG
              Delete the record IFACE.PROG then run the update scripts if updating is enabled.

       The  string  IFACE.PROG may not contain spaces, slashes, an initial dot, an initial hyphen
       or an initial tilde.  It is conventionally formed from IFACE, the name  of  the  interface
       involved,  a  dot,  and  IPROG,  the  name  of  the interface configuration program, e.g.,

       -u     Just run the update scripts (if updating is enabled).

       -i     List interfaces providing DNS configuration.

       --list | -l
              Show DNS configuration  for  each  interfact  in  resolv.conf  format  without  any

       With -a, -d or -u:
              if  updating is not enabled, schedule a delayed update.  The delayed update will be
              carried out when updates are enabled.

              Set the flag indicating that resolvconf should run update scripts when  invoked  in
              the  future  with  -a, -d or -u.  If a delayed update was scheduled then run update

              Clear the flag.

              Return 0 if the flag is set, otherwise return 1.

              Print the resolvconf version.

       --help | -h
              Print a short usage notice.


       The following variables can be set in the configuration file /etc/default/resolvconf.   If
       the file does not exist you will have to create it.

              If set to "yes" then resolvconf will print a message when /etc/resolv.conf is not a
              symbolic link to the resolvconf-generated resolver configuration file.  Set to "no"
              to prevent the printing of this message.  The default is "yes".

              If  set  to  "yes"  then  the libc script will include no more nameserver addresses
              after the first nameserver address that is a loopback address.  (In IPv4 a loopback
              address  is  any  one  that  starts  with  "127.".  In IPv6 the loopback address is

              The advantage of truncating the nameserver list after a loopback  address  is  that
              doing so inhibits unnecessary changes to resolv.conf and thus reduces the number of
              instances in which the update-libc.d/ scripts have to be run.  When an interface is
              brought  up  or  down  the  local  caching  nameserver that listens on the loopback
              address is still informed of the change and adapts accordingly; the clients of  the
              resolver  which  use the local caching nameserver do not need to be notified of the
              change.  A disadvantage of this mode of operation  is  that  applications  have  no
              secondary  or  tertiary nameserver address to fall back on should the local caching
              nameserver crash.  Insofar as a local  nameserver  crash  can  be  regarded  as  an
              unlikely  event,  this  is a relatively minor disadvantage.  Set to "no" to disable
              truncation.  The default is "yes".

              A deprecated synonym for this variable is TRUNCATE_NAMESERVER_LIST_AFTER_127.


              See the ENVIRONMENT VARIABLES section.

              Determines the order of precedence of nameserver addresses and search domain names.
              See above and interface-order(5).

              File containing basic resolver information.  The lines in this file are included in
              the resolver configuration file even when no interfaces are configured.

              File to be prepended to the  dynamically  generated  resolver  configuration  file.
              Normally this is just a comment line.

              File  to  be appended to the dynamically generated resolver configuration file.  To
              append nothing, make this an empty file.  This file  is  a  good  place  to  put  a
              resolver options line if one is needed, e.g.,

                  options inet6

              Copy  of  the  /etc/resolv.conf  file  before the resolvconf package was installed.
              This file has no effect on the functioning of resolvconf; it is  retained  so  that
              /etc/resolv.conf can be restored to its original state if the resolvconf package is

              Note also that a copy of this file is included in  the  database  until  the  first
              reboot  after installation of the resolvconf package; this ensures that nameservers
              reachable before installation of resolvconf are still reachable after  installation
              of resolvconf even though at that point not all suppliers of nameserver information
              may have supplied their information to resolvconf(8).

              Note also  that  the  administrator  can  choose  to  create  a  symbolic  link  in
              /etc/resolvconf/resolv.conf.d/  from  tail  to  original  so  that  the contents of
              original are always added to the end of the dynamically generated file.


       Currently resolvconf does not check the sanity of the information provided to it.


       Written by Thomas Hood <> with contributions by Nathan Stratton Treadway.


       Copyright © 2004-2013 Thomas Hood.
       This is free software; see the source for copying conditions.


       interface-order(5), resolv.conf(5), resolver(3).

       Read the resolvconf package README file for more in-depth information.