cat FILE | resolvconf -a IFACE.PROG
resolvconf -d IFACE.PROG
resolvconf --enable-updates | --disable-updates | --updates-are-enabled
The resolvconf package comprises a simple database for run-time nameserver information and a simple framework for notifying applications of changes in that information. Resolvconf thus sets itself up as the intermediary between programs that supply nameserver information and applications that use that information.
Information is added to or removed from the database using the resolvconf program. See the OPTIONS section below for a discussion of the available options.
Normally the resolvconf program is run only by network interface configuration programs such as ifup(8), ifdown, NetworkManager(8), dhclient(8), and pppd(8); and by local nameservers such as dnsmasq(8). These programs obtain nameserver information from some source and push it to resolvconf.
To add a nameserver IP address, add an option line consisting of dns-nameserver and the address. To add multiple nameserver addresses, include multiple such dns-nameserver lines.
dns-nameserver 192.168.1.254 dns-nameserver 18.104.22.168
To add search domain names, add a line beginning with dns-search.
dns-search foo.org bar.com
The dns-nameservers option is also accepted and, unlike dns-nameserver, can be given multiple arguments, separated by spaces.
The dns-domain option is deprecated in favor of dns-search.
The resulting stanza might look like the following example.
iface eth0 inet static address 192.168.1.3 netmask 255.255.255.0 gateway 192.168.1.1 dns-nameserver 192.168.1.254 dns-nameserver 22.214.171.124 dns-search foo.org bar.com
N.B.: On a machine where resolvconf has just been or is about to be installed and which previously relied on a static /etc/resolv.conf file,
Nameserver information provided to resolvconf is stored for use by subscribers to resolvconf's notification service. Subscriber packages 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. Client hook scripts will find the files containing nameserver information in the current directory.
The dynamically generated resolver configuration file always starts with the contents of /etc/resolvconf/resolv.conf.d/head and ends with the contents of /etc/resolvconf/resolv.conf.d/tail. Between head and tail the libc script inserts dynamic nameserver information compiled from, first, information provided for configured interfaces; second, static information from /etc/resolvconf/resolv.conf.d/base. Specifically, it writes:
To make the resolver use this dynamically generated resolver configuration file the administrator should ensure that /etc/resolv.conf is a symbolic link to /run/resolvconf/resolv.conf. This link is normally created on installation of the resolvconf package. The link is never modified by the resolvconf program itself. If you find that /etc/resolv.conf is not being updated, please check to make sure 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) should work fine with resolvconf.
Subscriber packages 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/. (For example, two packages that install update-libc.d/ hook scripts are fetchmail and squid.) 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/.
The string IFACE.PROG may not contain spaces, slashes, an initial dot, an initial hyphen or an initial tilde. It is conventionally formed from IFACE, the name of the interface involved, a dot, and IPROG, the name of the interface configuration program, e.g., "eth0.dhclient".
The following variables can be set in the configuration file /etc/default/resolvconf. If the file does not exist you will have to create it.
Note also that a copy of this file is included in the database until the first reboot after installation of the resolvconf package; this ensures that nameservers reachable before installation of resolvconf are still reachable after installation of resolvconf even though at that point not all suppliers of nameserver information may have supplied their information to resolvconf(8).
Note also that the administrator can choose to create a symbolic link in /etc/resolvconf/resolv.conf.d/ from tail to original so that the contents of original are always added to the end of the dynamically generated file.
Currently resolvconf does not check the sanity of the information provided to it.
Written by Thomas Hood <email@example.com> with contributions by Nathan Stratton Treadway.
Copyright © 2004-2013 Thomas Hood. This is free software; see the source for copying conditions.
interface-order(5), resolv.conf(5), resolver(3).
Read the resolvconf package README file for more in-depth information.