Do you use the trackpad on your Mac laptop for clicking (via the Trackpad Gestures section of the Trackpad tab in the Keyboard & Mouse System Preferences panel)? I do, and for me, it’s one of those things that quickly becomes natural—if I’m ever using someone else’s machine and they haven’t enabled this feature, I’ll often be tapping on the trackpad in frustration, wondering what’s wrong with it.
Outside of using someone else’s Mac, though, there’s a spot on your own machine where trackpad tapping is disabled: the login window. Granted, there are many great ways to navigate the login window—you can use the mouse, obviously, but you can also type a letter in someone’s user name to select it, press Return, enter the password, and press Return again. (This is the method that I usually use.) However, tapping on the trackpad is so ingrained in my brain now that I sometimes find myself tapping, wondering why nothing is happening.
The reason that tapping doesn’t work at the login window is because the setting to enable it is a user-level setting, and the login window is (obviously) not being run as any one user. You can, however, make trackpad taps work in this screen with a simple Terminal command. Open Terminal (in Applications -> Utilities), enter the following command, and press Return:
defaults write /Library/Preferences/.GlobalPreferences com.apple.mouse.tapBehavior -int 1
(That’s all one line, though the backslash should let you copy and paste it without difficulty. If you do type it by hand, remove the backslash, leaving the space after .GlobalPreferences.) The next time you logout (or call up the login window via Fast User Switching), you’ll find that trackpad tapping works as it does everywhere else.
Note that there’s one side effect to this change: all new user accounts will be created with trackpad tapping enabled. However, you can go to the Keyboard & Mouse System Preferences panel for the new user and uncheck the Clicking box on the Trackpad tab. This change, again because it’s a user-level change, will only affect the new user, so trackpad tapping will still work at the login window.
If you’d ever like to disable this in the future, repeat the above command, but put a 0 at the end instead of a 1.