After installing a new version of Ubuntu 17.10 I've found that my touchpad doesn't work properly. It doesn't click when I tap.
It took for a while to figure out that a new version switched from "xorg-synaptics" to "libinput". And for some interesting reasons "libinput" doesn't have tap to click enabled by default. So long story is short, here is a recipe to enable it:
1. Add following option to touchpad section in "/usr/share/X11/xorg.conf.d/40-libinput.conf"
Option "Tapping" "true"
2. Reboot and enjoy your touchpad again.
