Ubuntu Desktop 12.04 uses dnsmasq to perform DNS lookups, but it is not configured to cache these results. (I have checked this by using dig to resolve names and I do not see a large improvement in the response time after the first lookup.) How do I configure the NetworkManager-controlled dnsmasq to cache the results of DNS lookups?

in 12.04 dnsmasq is started by NetworkManager with hard-coded (i.e. not configurable) parameter --cache-size=0.

manpages for dnsmasq says setting cache-size to zero disables caching. If you want to enable caching, you will probably have to disable the dnsmasq-plugin for NetworkManager to prevent NetworkManager from starting dnsmasq and start your own instance of dnsmasq with cache-size greater then zero.

here you can read how to disable dnsmasq-plugin for NetworkManager: https://askubuntu.com/a/131422/71057

In Ubuntu 12.10 you can enable the cache of the NetworkManager-controlled dnsmasq instance by putting the line

cache-size=1000

(with your preferred number of names instead of 1000) in a new file in /etc/NetworkManager/dnsmasq.d/. To activate this change you must then do

sudo stop network-manager
sudo killall dnsmasq
sudo start network-manager

or reboot.

I didn't want to upgrade from 12.04, but still wanted dnsmasq managed by NetworkManager with caching enabled, but as the other answer said, --cache-size=0 is hard-coded and can't be changed with configuration.

So what I ended up doing was the following, as root:

mv /usr/sbin/dnsmasq /usr/sbin/dnsmasq.real

and then creating a new file, /usr/sbin/dnsmasq with the following content:

#!/bin/bash
args=$(echo "$@" | sed 's/--cache-size=0/--cache-size=1000/')
/usr/sbin/dnsmasq.real $args

make sure you chmod +x /usr/sbin/dnsmasq, and change the cache-size from 1000 to whatever you want, enjoy your LTS release with a DNS cache!

I was able to enable DNS caching in Linux Mint 13 (based on Ubuntu 12.04) using the method described in the first answer. I created a file /etc/NetworkManager/dnsmasq.d/cachedns containing the line cache-size=100, then restarted network-manager. Even though dnsmasq is executed by network-manager with a hard-coded --cache-size=0 on its command line, setting the cache-size in a config file overrides that value. You can verify that it works by doing this:

sudo killall -USR1 dnsmasq
tail /var/log/syslog

You should see a line that looks like this in the syslog, showing the cache size:

dnsmasq[17808]: cache size 100, 0/2 cache insertions re-used unexpired cache entries.

To re-enable the cache (with a NetworkManager version that has the /etc/NetworkManager/dnsmasq.d directory), it is actually sufficient to drop a file in that directory with content "cache-size=X" (with X being 150 for the default dnsmasq would have). The files in there override the hard-coded parameters given on the commandline.

In Ubuntu 14.04, I had to edit /etc/default/dnsmasq and set ENABLED=1

I also put cache-size=1000 there and in all the other dnsmasq config files that I found.