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 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 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.
When an interface goes down, it should then call
resolvconf with
-d interface arguments to delete the
resolv.conf file for the
interface.
Here are some more options that
resolvconf has:-
-I
Initialise the state directory /var/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.
-f
Ignore non existant interfaces. Only really useful for deleting interfaces.
-i pattern
List the interfaces, 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 that match it.
-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.
-u
Force resolvconf to update all it's 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 options designed to be used by it's subscribers:-
-v
Echo variables DOMAINS, SEARCH and NAMESERVERS so that the subscriber can configure the resolver easily.