/etc/X11/xorg.conf.d/50-synaptics.conf:
Section "InputClass"
Identifier "touchpad catchall custom"
Driver "synaptics"
MatchIsTouchpad "on"
# This option is recommend on all Linux systems using evdev, but cannot be
# enabled by default. See the following link for details:
# http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
MatchDevicePath "/dev/input/event*"
Option "TapButton1" "1"
Option "TapButton2" "2"
Option "HorizTwoFingerScroll" "1"
EndSection
… e desabilite o daemon do mouse do Gnome via
dconf write /org/gnome/settings-daemon/plugins/mouse/active false
Reinicie o xorg.