Enable horizontal scrolling in Ubuntu

There’s a way through dconf Editor; so:

1. open dconf Editor through the Dash;
2. go to org > gnome > settings-daemon > peripherals > touchpad;
3. check horiz-scroll-enabled, as you see in the screenshot.

Edit: Dconf Editor was pre-installed on 13.04, where I first faced the problem; but on 13.10 and 14.04 it’s easier to use gsettings, see Samuel Cavazos’s answer.

Alternative way: run this in your command line

synclient HorizTwoFingerScroll=1

Or just run

gsettings set org.gnome.settings-daemon.peripherals.touchpad horiz-scroll-enabled "true"

in a terminal