NAME¶
resolvconf
—
a framework for managing multiple DNS
configurations
SYNOPSIS¶
resolvconf |
[ -m
metric ]
[-p ]
[-x ]
-a
interface[.protocol ]
<file |
resolvconf |
[ -f ]
-d
interface[.protocol ] |
resolvconf |
[ -x ]
-il
pattern |
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(3) 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.
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.
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.
SEE ALSO¶
resolv.conf(5),
resolvconf.conf(5),
resolver(3),
stdin(3)
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.