Provided by: resolvconf_1.63ubuntu11_all
resolvconf - manage nameserver information
cat FILE | resolvconf -a IFACE.PROG
resolvconf -d IFACE.PROG
resolvconf --enable-updates | --disable-updates | --updates-are-enabled
| --create-runtime-directories | --wipe-runtime-directories
Overwrite (-a) or delete (-d) the nameserver information record
IFACE.PROG. Also run the update scripts in /etc/resolvconf/update.d/
if the nameserver information has changed and updating is enabled.
With -u, just run the update scripts if updating is enabled.
With -a, -d or -u schedule a delayed update if updating is not
Normally resolvconf is run only by hook scripts attached to network
interface configurers such as pppd(8) (for ppp interfaces), to DHCP
clients such as dhclient(8), to ifup(8) and ifdown, and to DNS caches
such as dnsmasq(8) (for the loopback interface). These hook scripts
furnish resolvconf with information about nameservers. For example,
dhclient receives one or more nameserver addresses during its
negotiation with the DHCP server; its hook script /etc/dhcp/dhclient-
enter-hooks.d/resolvconf pushes this information to resolvconf.
The ifup(8) program can be used to configure network interfaces
according to settings in /etc/network/interfaces(5). To make ifup push
nameserver information to resolvconf when it configures an interface,
add dns- lines to the relevant iface stanza in /etc/network/interfaces.
To add nameserver addresses add a line beginning with dns-nameservers.
dns-nameservers 126.96.36.199 188.8.131.52
Note that one or more addresses can be given, and note the `s' at the
end of the option name. (Contrast with the resolv.conf(5) option
nameserver.) For each other valid resolv.conf(5) configuration option,
you can include, in the stanza, one line beginning with that option
name with a dns- prefix. The resulting stanza might look like the
iface eth0 inet static
dns-nameservers 192.168.3.45 192.168.8.10
dns-search foo.org bar.com
See the resolvconf package's README file for more detailed information.
For more information about the dns-* options, e.g., dns-search, see
The administrator can run resolvconf from the command line to add or
delete nameserver information, but this is not normally necessary.
Nameserver information provided to resolvconf is stored for use by
subscribers to resolvconf's notification service. Subscribers 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.
The most important piece of software that subscribes to the
notification service is the set of functions that make up the GNU C
Library resolver(3). When nameserver information is updated, the
script /etc/resolvconf/update.d/libc writes a new resolver
configuration file to /run/resolvconf/resolv.conf and then runs the
scripts in /etc/resolvconf/update-libc.d/. To make the resolver use
the 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 never modified by
resolvconf(8). If you find that /etc/resolv.conf is not being updated,
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 with the GNU C Library
resolver) should work with resolvconf(8).
Subscribers 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/. 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/. Examples of packages that do this are
fetchmail(1) and squid(8).
Client hook scripts will find the files containing nameserver
information in the current directory.
Add or overwrite the record IFACE.PROG. 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.
Delete the record IFACE.PROG.
The string IFACE.PROG name 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 PROG,
the name of the interface configuration program, e.g., `eth0.dhclient'.
Following the addition or deletion of the record, run the update
scripts (if updating is enabled).
-u Just run the update scripts (if updating is 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 scripts.
Clear the flag.
Return 0 if the flag is set, otherwise return 1.
Create the directories where resolver information records and
other run-time files are stored.
Delete everything in the directories where resolver information
records and other run-time files are stored.
The following variables can be set in the default-override file
/etc/default/resolvconf. If the file does not exist you will have to
If set to "yes" then resolvconf will print a message when
/etc/resolv.conf is not a symbolic link to the
resolvconf(8)-generated resolv.conf file. Set to "no" to
prevent the printing of this message. The default is "yes".
If set to "yes" then the update.d/libc script will include no
more nameserver addresses after the first loopback address. In
IPv4 a loopback address is an address that starts with "127."
This is usually the preferable behavior if the nameserver at
127.* is a local caching nameserver since it inhibits
unnecessary changes to resolv.conf. When an interface is
brought up the local caching nameserver is informed by
resolvconf(8) of any new nameserver addresses and the additional
name service is made available to applications that make use of
the resolver and the local caching nameserver; the applications
themselves 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 this
truncation feature. The default is "yes". A deprecated synonym
for this variable is TRUNCATE_NAMESERVER_LIST_AFTER_127.
See the ENVIRONMENT VARIABLES section.
This is the location where nameserver information is stored. It
will be created if resolvconf is called with the
--create-runtime-directories option. Clients should not make
any assumptions about the hierarchy that is constructed under
Determines the order in which nameserver information records are
processed. See 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.,
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 if
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 the latter are always added to the end of
the dynamically generated resolv.conf.
Currently resolvconf does not check the sanity of the information
provided to it.
Written by Thomas Hood <email@example.com>.
Copyright (C) 2004, 2011 Thomas Hood
This is free software; see the source for copying conditions.
interface-order(5), resolv.conf(5), resolver(3).