Ubuntu Manpage: resolvconf — a framework for managing multiple DNS configurations

NAME

     resolvconf — a framework for managing multiple DNS configurations

SYNOPSIS

     resolvconf -I
     resolvconf [-m metric] [-p] [-x] -a interface[.protocol] <file
     resolvconf [-f] -d interface[.protocol]
     resolvconf [-x] -il pattern
     resolvconf -u
     resolvconf --version

DESCRIPTION

resolvconf manages resolv.conf(5) files from multiple sources, such as DHCP and VPN clients.
Traditionally, the host runs just one client and that updates /etc/resolv.conf. More modern
systems frequently have wired and wireless interfaces and there is no guarantee both are on
the same network. With the advent of VPN and other types of networking daemons, many things
now contend for the contents of /etc/resolv.conf.

resolvconf solves this by letting the daemon send their resolv.conf(5) file to resolvconf
via stdin(4) with the argument -a interface[.protocol] instead of the filesystem.
resolvconf then updates /etc/resolv.conf as it thinks best. When a local resolver other
than libc is installed, such as dnsmasq(8) or named(8), then resolvconf will supply files
that the resolver should be configured to include.

resolvconf assumes it has a job to do. In some situations resolvconf needs to act as a
deterrent to writing to /etc/resolv.conf. Where this file cannot be made immutable or you
just need to toggle this behaviour, resolvconf can be disabled by adding resolvconf=NO to
resolvconf.conf(5).

resolvconf can mark an interfaces resolv.conf as private. This means that the name servers
listed in that resolv.conf are only used for queries against the domain/search listed in the
same file. This only works when a local resolver other than libc is installed. See
resolvconf.conf(5) for how to configure resolvconf to use a local name server and how to
remove the private marking.

resolvconf can mark an interfaces resolv.conf as exclusive. Only the latest exclusive
interface is used for processing, otherwise all are.

When an interface goes down, it should then call resolvconf with -d interface.* arguments to
delete the resolv.conf file(s) for all the protocols on the interface.

Here are some options for the above commands:-

-f Ignore non existent interfaces. Only really useful for deleting interfaces.

-m metric Set the metric of the interface when adding it, default of 0. Lower metrics
take precedence. This affects the default order of interfaces when listed.

-p Marks the interface resolv.conf as private.

-x Mark the interface resolv.conf as exclusive when adding, otherwise only use the
latest exclusive interface.

resolvconf has some more commands for general usage:-

-i pattern List the interfaces and protocols, optionally matching pattern, we have
resolv.conf files for.

-l pattern List the resolv.conf files we have. If pattern is specified then we list the
files for the interfaces and protocols that match it.

-u Force resolvconf to update all its subscribers. resolvconf does not update the
subscribers when adding a resolv.conf that matches what it already has for that
interface.

--version Echo the resolvconf version to stdout.

resolvconf also has some commands designed to be used by it's subscribers and system
startup:-

-I Initialise the state directory /run/resolvconf. This only needs to be called
if the initial system boot sequence does not automatically clean it out; for
example the state directory is moved somewhere other than /var/run. If used,
it should only be called once as early in the system boot sequence as possible
and before resolvconf is used to add interfaces.

-R Echo the command used to restart a service.

-r service If the service is running then restart it. If the service does not exist or is
not running then zero is returned, otherwise the result of restarting the
service.

-v Echo variables DOMAINS, SEARCH and NAMESERVERS so that the subscriber can
configure the resolver easily.

-V Same as -v except that only the information configured in resolvconf.conf(5) is
set.

INTERFACE ORDERING

     For resolvconf to work effectively, it has to process the resolv.confs for the interfaces in
     the correct order.  resolvconf first processes interfaces from the interface_order list,
     then interfaces without a metic and that match the dynamic_order list, then interfaces with
     a metric in order and finally the rest in the operating systems lexical order.  See
     resolvconf.conf(5) for details on these lists.

PROTOCOLS

     Here are some suggested protocol tags to use for each resolv.conf file registered on an
     interface:-

     dhcp         Dynamic Host Configuration Protocol.  Initial versions of resolvconf did not
                  recommend a protocol tag be appended to the interface name.  When the protocol
                  is absent, it is assumed to be the DHCP protocol.

     ppp          Point-to-Point Protocol.

     ra           IPv6 Router Advertisement.

     dhcp6        Dynamic Host Configuration Protocol, version 6.

IMPLEMENTATION NOTES

     If a subscriber has the executable bit then it is executed otherwise it is assumed to be a
     shell script and sourced into the current environment in a subshell.  This is done so that
     subscribers can remain fast, but are also not limited to the shell language.

     Portable subscribers should not use anything outside of /bin and /sbin because /usr and
     others may not be available when booting.  Also, it would be unwise to assume any shell
     specific features.

ENVIRONMENT

     IF_METRIC
     If the -m option is not present then we use IF_METRIC for the metric.

     IF_PRIVATE
     Marks the interface resolv.conf as private.

     IF_EXCLUSIVE
     Marks the interface resolv.conf as exclusive.

FILES

     /etc/resolv.conf.bak
     Backup file of the original resolv.conf.

     /etc/resolvconf.conf
     Configuration file for resolvconf.

     /lib/resolvconf
     Directory of subscribers which are run every time resolvconf adds, deletes or updates.

     /lib/resolvconf/libc.d
     Directory of subscribers which are run after the libc subscriber is run.

     /run/resolvconf
     State directory for resolvconf.

HISTORY

     This implementation of resolvconf is called openresolv and is fully command line compatible
     with Debian's resolvconf, as written by Thomas Hood.

AUTHORS

     Roy Marples <roy@marples.name>

BUGS

     Please report them to http://roy.marples.name/projects/openresolv

     resolvconf does not validate any of the files given to it.

     When running a local resolver other than libc, you will need to configure it to include
     files that resolvconf will generate.  You should consult resolvconf.conf(5) for instructions
     on how to configure your resolver.