To make your scrollbar always visible, write this in terminal:
sudo gsettings set com.canonical.desktop.interface scrollbar-mode normal
gsettings
is to get/set system settings, and you're setting the scrollbar-mode
to normal, you need sudo
because you're making changes to the system.
To reset to default behaviour:
sudo gsettings reset com.canonical.desktop.interface scrollbar-mode
You can also achieve the same via Unity tweak tool. If you do not have it installed you can install it:
sudo apt-get install unity-tweak-tool
Then under System menu go to Scrolling > Under Scrollbars, change from overlay to Legacy.
There's no current way to set the 'overlay' to always appear. Setting your scrollbars to normal
turns the 'hover to show' off.