The dnsmasq startup script is
/etc/init.d/dnsmasq. It's called by symlinks from the /etc/rcX.d/ directories, for example:
If you don't want it to start, you can remove the package with
sudo apt-get remove dnsmasq. Or you can leave it installed and just remove all symlinks from the /etc/rcX.d/ directories with the command:
update-rc.d -f dnsmasq remove.
You can also edit
/etc/default/dnsmasq and change "ENABLED=1" to "ENABLED=0" which will also tell it not to run in daemon mode.
Lastly, you can disable just the DHCP function by editing
/etc/dnsmasq.conf and adding lines for your interfaces that you don't want DHCP on by adding, for example: "no-dhcp-interface=eth0". You might do this if you still wanted to use the DNS functionality.
Note: sometimes dnsmasq is installed as
dnsmasq-base instead of
dnsmasq in order to work with other packages such as NetworkManager (when sharing an internet connection) or Libvirt (for giving addresses to virtual machines).