NAME¶

resolvconf — a framework for managing multiple DNS configurations

SYNOPSIS¶

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 key 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.

At it's heart, resolvconf is a key/value store for resolv.conf files. Each entry must have a unique key and should be expressed as interface.protocol so that it's easy to tell from where the resolv.conf file came from. This also allows using pattern matching such as interface.* to match all protocols running on the interface. For example, a modern system will likely run DHCP, RA and DHCPv6 which could be from separate programs or one program running many protocols. However, this is not a fixed requirement, resolvconf will work with any key name and it should be treated as an opaque value outside of resolvconf.

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 a resolv.conf as private and optionally non-searchable. 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 and if non-searchable then the domain/search listed are excluded from the global search list defined in /etc/resolv.conf. 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 a resolv.conf as exclusive. Only the latest exclusive key is used for processing, otherwise all are.

When a configuration source goes away, such as an interface going down or a VPN stopping, it should then call resolvconf with -d key arguments to clean up the resolv.conf it added previously. For systems that support the concept of persisting configuration when the source is suspended, such as the carrier going down, then it should instead call resolvconf with -C key arguments to deprecate the entry -c key to activate the entry when it comes back again. This only affects the order in which the resolv.conf entries are processed.

Here are some options for the above commands:

-f

Ignore non existent resolv.conf entries. Only really useful for deleting.

-m metric

Set the metric of the resolv.conf entry when adding it, default of 0. Lower metrics take precedence. This affects the default order of entires when listed.

-p [pattern]

Marks the resolv.conf as private if the -a command is given, otherwise resolv.conf entries having their key matching pattern are listed. If an extra -p is given then the resolv.conf is marked as non-searchable as well.

-x

Mark the resolv.conf as exclusive when adding, otherwise only use the latest exclusive key.

resolvconf has some more commands for general usage:

-i [pattern]

List the keys stored, optionally matching pattern, we have resolv.conf files for. If the -L option is given first, then the keys will be list post-processed.

-L [pattern]

List the resolv.conf files we have, post-processed by the resolvconf.conf(5) configuration. If pattern is specified then we list the files for the keys which match it.

-l [pattern]

List the resolv.conf files we have. If pattern is specified then we list the files for the keys which match it. 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 key.

--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 entries.

-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.

RESOLV.CONF ORDERING¶

For resolvconf to work effectively, it has to process the resolv.conf entries in the correct order. resolvconf first processes keys from the key_order list, then entries without a metric and that match the dynamic_order list, then entries 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

dhcp

Dynamic Host Configuration 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 resolv.conf as private.

IF_NOSEARCH

Marks the resolv.conf as non-searchable.

IF_EXCLUSIVE

Marks the resolv.conf as exclusive.

FILES¶

/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.

NOTES¶

Domain labels are assumed to be in ASCII and are converted to lower case to avoid duplicate zones when given differing case from different sources.

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.

SEE ALSO¶

resolver(3), stdin(4), resolv.conf(5), resolvconf.conf(5)

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