resolvconf —
a
framework for managing multiple DNS configurations
resolvconf |
[-m
metric]
[-p]
[-x]
-a
interface[.protocol]
<file
|
resolvconf |
[-f]
-d
interface[.protocol] |
resolvconf |
[-x]
-il
pattern
|
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. For systems that support the
concept of persisting configuration when the carrier goes down, then it should
instead call
resolvconf with
-C interface.*
arguments to deprecate the matching interfaces and
-c interface.*
to activate the matching interfaces when the carrier comes up. This only
affects the order in which interfaces are processed.
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.
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.
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.
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.
- 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.
- /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.
resolver(3),
stdin(4),
resolv.conf(5),
resolvconf.conf(5)
This implementation of
resolvconf is called
openresolv and is fully command line compatible with Debian's resolvconf, as
written by Thomas Hood.
Roy Marples
<
[email protected]>
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.