resolvconf.openresolv - Man Page

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 its 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 metric 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.

/usr/lib/resolvconf

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

/usr/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 <roy@marples.name>

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.