Tap-to-click in Debian

Tapping on a touchpad is a common alternative to clicking a mouse button because it is often more convenient given your hand's position. In Debian, this is often not enabled by default, but it can easily be enabled.

All the following commands should be run as root.

Stretch

In Stretch, the old Synaptics driver is being made obsolete in favour of the libinput driver, so first, you will want to uninstall the xserver-xorg-input-synaptics package, with the following command: # apt remove xserver-xorg-input-synaptics.

Then, make sure that the xserver-xorg-input-libinput package is installed: # apt install xserver-xorg-input-libinput.

Now, you need to override the default configuration by creating any file, such as /etc/X11/xorg.conf.d/40-libinput.conf and giving it the following content:

Section "InputClass"
	Identifier "libinput touchpad catchall"
	MatchIsTouchpad "on"
	MatchDevicePath "/dev/input/event*"
	Driver "libinput"
	Option "Tapping" "on"
EndSection

You can do this either by creating the file and entering the content manually (copy-paste into a text editor) or by executing the following command:

# echo 'Section "InputClass"
        Identifier "libinput touchpad catchall"
        MatchIsTouchpad "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
        Option "Tapping" "on"
EndSection' > /etc/X11/xorg.conf.d/40-libinput.conf

If the /etc/X11/xorg.conf.d/ directory doesn't exist, just create it.

This configuration can be further adapted to suit your preferences.

Now, simply restart your desktop manager, which could be, for example: # systemctl restart lightdm or # systemctl restart gdm3.

Jessie

In Jessie, you must simply override the default configuration by creating /etc/X11/xorg.conf.d/50-synaptics.conf and entering the following content:

Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
        Option "TapButton1" "1"
        Option "TapButton2" "3"

Again, this can be done manually, or with this command:

# echo 'Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
        Option "TapButton1" "1"
        Option "TapButton2" "3"' > /etc/X11/xorg.conf.d/50-synaptics.conf

Finally, reboot your system.

References and further reading

I had this problem myself. I solved it using information gleaned mainly from the answers in this Unix StackExchange thread and from the Debian Wiki page. The content on this page is a combination of content from those two sources.