Last Friday I was presented a unibody MacBook Pro with limited function of the new glass trackpad. Some gestures would work, but others wouldn’t. The first step in most any repair is to reset the SMC/PMU and PRAM, and then run Software Update, but these had no effect – even the trackpad firmware update didn’t help.

Knowing that the user on the machine was created by Migration Assistant, and that many problems like this are actually software based, I decided to create a new admin user on the machine. Turns out the trackpad worked fine under the clean user! Had the trackpad refused to work in the new user, I’d suspect hardware to be responsible; since the trackpad worked fine in the new user, I had to figure out what piece of the operating system was causing the failure.

First stop was the Preferences folder in the customer’s home folder. Looking through each and every one of the files, none jumped out at me as being possibly responsible for the behavior. After a bit of head scratching, I remembered that there are many invisible files on a Mac’s hard drive. These are files that begin with a period, like .GlobalPreferences.plist. But how to see these files if they’re invisible?

Well, the easiest way is through Terminal. To see a complete list of all files in a folder, type ls -a. The output for ~/Library/Preferences would show you several files near the top whose names begin with a period. In fact, .GlobalPreferences.plist was to blame here. I deleted it through the terminal using the rm command, restarted the computer, and all was well.

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