resolvconf.8.in

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.Dd April 21, 2025
.Dt RESOLVCONF 8
.Os
.Sh NAME
.Nm resolvconf
.Nd a framework for managing multiple DNS configurations
.Sh SYNOPSIS
.Nm
.Fl I
.Nm
.Op Fl m Ar metric
.Op Fl p
.Op Fl x
.Fl a Ar interface Ns Op Ar .protocol
.No < Ns Pa file
.Nm
.Fl C Ar pattern
.Nm
.Fl c Ar pattern
.Nm
.Op Fl f
.Fl d Ar interface Ns Op Ar .protocol
.Nm
.Op Fl x
.Fl iLlp Ar pattern
.Nm
.Fl u
.Nm
.Fl Fl version
.Sh DESCRIPTION
.Nm
manages
.Xr resolv.conf 5
files from multiple sources, such as DHCP and VPN clients.
Traditionally, the host runs just one client and that updates
.Pa /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
.Pa /etc/resolv.conf .
.Pp
.Nm
solves this by letting the daemon send their
.Xr resolv.conf 5
file to
.Nm
via
.Xr stdin 4
with the argument
.Fl a Ar interface Ns Op Ar .protocol
instead of the filesystem.
.Nm
then updates
.Pa /etc/resolv.conf
as it thinks best.
When a local resolver other than libc is installed, such as
.Xr dnsmasq 8
or
.Xr named 8 ,
then
.Nm
will supply files that the resolver should be configured to include.
.Pp
.Nm
assumes it has a job to do.
In some situations
.Nm
needs to act as a deterrent to writing to
.Pa /etc/resolv.conf .
Where this file cannot be made immutable or you just need to toggle this
behaviour,
.Nm
can be disabled by adding
.Sy resolvconf Ns = Ns NO
to
.Xr resolvconf.conf 5 .
.Pp
.Nm
can mark an interfaces
.Pa resolv.conf
as private.
This means that the name servers listed in that
.Pa 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
.Xr resolvconf.conf 5
for how to configure
.Nm
to use a local name server and how to remove the private marking.
.Pp
.Nm
can mark an interfaces
.Pa resolv.conf
as exclusive.
Only the latest exclusive interface is used for processing, otherwise all are.
.Pp
When an interface goes down, it should then call
.Nm
with
.Fl d Ar interface.*
arguments to delete the
.Pa resolv.conf
file(s) for all the
.Ar protocols
on the
.Ar interface .
For systems that support the concept of persisting configuration when
the carrier goes down, then it should instead call
.Nm
with
.Fl C Ar interface.*
arguments to deprecate the matching interfaces and
.Fl c Ar interface.*
to activate the matching interfaces when the carrier comes up.
This only affects the order in which interfaces are processed.
.Pp
Here are some options for the above commands:-
.Bl -tag -width pattern_opt
.It Fl f
Ignore non existent interfaces.
Only really useful for deleting interfaces.
.It Fl m Ar 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.
.It Fl p Op Ar pattern
Marks the interface
.Pa resolv.conf
as private if the
.Fl a
command is given, otherwise private interfaces matching
.Ar pattern
are listed.
.It Fl x
Mark the interface
.Pa resolv.conf
as exclusive when adding, otherwise only use the latest exclusive interface.
.El
.Pp
.Nm
has some more commands for general usage:-
.Bl -tag -width pattern_opt
.It Fl i Op Ar pattern
List the interfaces and protocols, optionally matching
.Ar pattern ,
we have
.Pa resolv.conf
files for.
.It Fl L Op Ar pattern
List the
.Pa resolv.conf
files we have,
post-processed by the
.Xr resolvconf.conf 5
configuration.
If
.Ar pattern
is specified then we list the files for the interfaces and protocols
that match it.
.It Fl l Op Ar pattern
List the
.Pa resolv.conf
files we have.
If
.Ar pattern
is specified then we list the files for the interfaces and protocols
that match it.
.It Fl u
Force
.Nm
to update all its subscribers.
.Nm
does not update the subscribers when adding a resolv.conf that matches
what it already has for that interface.
.It Fl Fl version
Echo the resolvconf version to
.Em stdout .
.El
.Pp
.Nm
also has some commands designed to be used by its subscribers and
system startup:-
.Bl -tag -width pattern_opt
.It Fl I
Initialise the state directory
.Pa @VARDIR@ .
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
.Pa /var/run .
If used, it should only be called once as early in the system boot sequence
as possible and before
.Nm
is used to add interfaces.
.It Fl R
Echo the command used to restart a service.
.It Fl r Ar service
If the
.Ar 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.
.It Fl v
Echo variables DOMAINS, SEARCH and NAMESERVERS so that the subscriber can
configure the resolver easily.
.It Fl V
Same as
.Fl v
except that only the information configured in
.Xr resolvconf.conf 5
is set.
.El
.Sh INTERFACE ORDERING
For
.Nm
to work effectively, it has to process the resolv.confs for the interfaces
in the correct order.
.Nm
first processes interfaces from the
.Sy interface_order
list, then interfaces without a metric and that match the
.Sy dynamic_order
list, then interfaces with a metric in order and finally the rest in
the operating systems lexical order.
See
.Xr resolvconf.conf 5
for details on these lists.
.Sh PROTOCOLS
Here are some suggested protocol tags to use for each
.Pa resolv.conf
file registered on an
.Ar interface Ns No :-
.Bl -tag -width pattern_opt
.It dhcp
Dynamic Host Configuration Protocol.
Initial versions of
.Nm
did not recommend a
.Ar protocol
tag be appended to the
.Ar interface
name.
When the protocol is absent, it is assumed to be the DHCP protocol.
.It ppp
Point-to-Point Protocol.
.It ra
IPv6 Router Advertisement.
.It dhcp6
Dynamic Host Configuration Protocol, version 6.
.El
.Sh 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.
.Pp
Portable subscribers should not use anything outside of
.Pa /bin
and
.Pa /sbin
because
.Pa /usr
and others may not be available when booting.
Also, it would be unwise to assume any shell specific features.
.Sh ENVIRONMENT
.Bl -ohang
.It Va IF_METRIC
If the
.Fl m
option is not present then we use
.Va IF_METRIC
for the metric.
.It Va IF_PRIVATE
Marks the interface
.Pa resolv.conf
as private.
.It Va IF_EXCLUSIVE
Marks the interface
.Pa resolv.conf
as exclusive.
.El
.Sh FILES
.Bl -ohang
.It Pa /etc/resolv.conf.bak
Backup file of the original resolv.conf.
.It Pa @SYSCONFDIR@/resolvconf.conf
Configuration file for
.Nm .
.It Pa @LIBEXECDIR@
Directory of subscribers which are run every time
.Nm
adds, deletes or updates.
.It Pa @LIBEXECDIR@/libc.d
Directory of subscribers which are run after the libc subscriber is run.
.It Pa @VARDIR@
State directory for
.Nm .
.El
.Sh SEE ALSO
.Xr resolver 3 ,
.Xr stdin 4 ,
.Xr resolv.conf 5 ,
.Xr resolvconf.conf 5
.Sh HISTORY
This implementation of
.Nm
is called openresolv and is fully command line compatible with Debian's
resolvconf, as written by Thomas Hood.
.Sh AUTHORS
.An Roy Marples Aq Mt roy@marples.name
.Sh BUGS
Please report them to
.Lk http://roy.marples.name/projects/openresolv
.Pp
.Nm
does not validate any of the files given to it.
.Pp
When running a local resolver other than libc, you will need to configure it
to include files that
.Nm
will generate.
You should consult
.Xr resolvconf.conf 5
for instructions on how to configure your resolver.