How do I make modprobe changes permanent?

If you are using a generic synaptic touchpad, but it fails to respond to tapping or scrolling actions under a new installation, you can run the following two commands to immediately make it work:

modprobe -r psmouse
modprobe psmouse proto=imps

To make this change permanent, create a file such as touchpad.conf under /etc/modprobe.d/, and put the following line in it:

options psmouse proto=imps

Login as a super user (root) and open /etc/rc.local using nano or some other editor as shown below.

nano /etc/rc.local

and add the lines to the file

modprobe -r psmouse
modprobe psmouse proto=imps

Save Ctrl+O and Exit Ctrl+X and restart your system. It is done!