resolvconf - manage nameserver information

cat FILE | resolvconf -a INTERFACE

resolvconf -d INTERFACE

resolvconf -u

Overwrite (-a) or delete (-d) the nameserver information record for network interface INTERFACE and run the update scripts in /etc/resolvconf/update.d/.

With -u, just run the update scripts.

Normally resolvconf is run only by hook scripts attached to network interface configurers such as pppd(8) (for ppp interfaces), to DHCP clients such as dhclient3(8), to ifup(8) and ifdown, and to DNS caches such as dnsmasq(8) (for the loopback interface). However, the administrator can also run resolvconf from the command line to add or delete auxiliary nameserver information.

Nameserver information provided to resolvconf is stored for use by subscribers to resolvconf's notification service. Subscribers that need to know when nameserver information has changed should install a script in /etc/resolvconf/update.d/ (... or in /etc/resolvconf/update-libc.d/: see below). For example, DNS caches such as dnsmasq(8) and pdnsd(8) subscribe to the notification service so that they know whither to forward queries.

The most important piece of software that subscribes to the notification service is the set of functions that make up the GNU C Library resolver(3). When nameserver information is updated the script /etc/resolvconf/update.d/libc writes a new resolver configuration file to /etc/resolvconf/run/resolv.conf and then runs the scripts in /etc/resolvconf/update-libc.d/. To make the resolver use the dynamically generated resolver configuration file the administrator should ensure that /etc/resolv.conf is a symbolic link to /etc/resolvconf/run/resolv.conf. This link is never modified by /sbin/resolvconf. If you find that /etc/resolv.conf is not being updated, check to see that the link is intact.

The GNU C Library resolver library isn't the only resolver library available. However, any resolver library that reads /etc/resolv.conf (and most of them do, in order to be compatible with the GNU C Library resolver) should work with resolvconf.

Subscribers that need to know only when the resolver configuration file has changed should install a script in /etc/resolvconf/update-libc.d/ rather than in /etc/resolvconf/update.d/. (This is important for synchronization purposes: scripts in update-libc.d/ are run after resolv.conf has been updated; the same is not necessarily true of scripts in update.d/.) Examples of packages that do this are fetchmail(1) and squid(8).

Hook scripts will find the files containing nameserver information in the current directory.

-a INTERFACE

Add or overwrite the record for network interface INTERFACE. When this option is used the information must be provided to resolvconf on its standard input in the format of the resolv.conf(5) file. Each line in the file must be terminated by a newline.

-d INTERFACE

Delete the record for network interface INTERFACE.

The INTERFACE name may not contain spaces, slashes or initial dots, hyphens or tildes.

Following the addition or deletion of the record, resolvconf runs the update scripts as described in the CLIENTS section.

-u

Just run the update scripts.

/etc/resolvconf/run

This is either a directory where nameserver information can be stored or a symbolic link to such a directory. Clients should not make any assumptions about the canonical location of this directory or the hierarchy that is constructed under it.

/etc/resolvconf/interface-order

Determines the order in which nameserver information records are processed. See interface-order(5).

/etc/resolvconf/resolv.conf.d/base

File containing basic resolver information. The lines in this file are included in the resolver configuration file even when no interfaces are configured.

/etc/resolvconf/resolv.conf.d/head

File to be prepended to the dynamically generated resolver configuration file. Normally this is just a comment line.

/etc/resolvconf/resolv.conf.d/tail

File to be appended to the dynamically generated resolver configuration file. To append nothing, make this an empty file.

Currently resolvconf does not check the sanity of the information provided to it.

Written by Thomas Hood <jdthood@yahoo.co.uk>.

Copyright © 2004 Thomas Hood

This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

interface-order(5), resolv.conf(5), resolver(3).