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The Disk Utility program included with OS X can perform several Mac maintenance chores, including repairing disk permissions.

Q.In Mac OS X, what does the “Repair Disk Permissions” function of the Disk Utility app actually do?

A. OS X uses a system of disk permissions to control who and what have access to files and folders on the computer — and it essentially keeps a master list of what the permissions for each file should be. Among other things, having the correct permissions in place ensures that an installed program cannot modify read-only system files, and that one user’s personal files are kept private from others with user accounts on the same computer.

With time and use, actions like installing or uninstalling programs may inadvertently alter these permissions from their initial state. Incorrect permissions can occasionally cause erratic behavior like files that cannot be saved, programs that will not open or text that is scrambled. Repairing a Mac’s disk permissions is often advised as a basic troubleshooting step to fix these types of problems.

To do this, press the Command key and space bar on the keyboard, type “Disk Utility” in the Spotlight search box that appears and select the Disk Utility application when it pops up in the results list. With the Mac’s drive selected in the program’s window, click the First Aid tab and then the Repair Disk Permissions button.

As Disk Utility works to scan the system, it checks its original master list of permissions. In simple terms, if the program finds discrepancies, it changes those files’ permissions to match those on its master list.

During the process, you will see a list of messages about what is incorrect and what is getting repaired. Apple’s support site also has an entire document devoted to “Repair Disk Permissions messages you can safely ignore.” Disk Utility will display a “Permissions repair complete” message when the scan is finished.

The Dimming of Silverlight

Q.I occasionally get messages telling me to update “Silverlight.” Is this a real thing?

A. Silverlight is Microsoft’s platform for multimedia, similar to Adobe’s Flash software. Like Adobe Flash, Silverlight has its own plug-in for compatible browsers. If you come across a web page running Silverlight, you may see a message asking to install or upgrade the software for your browser.

Silverlight got a lot of use as the platform behind NBC’s online video streams of the 2008 Olympic Games, but Microsoft has since stopped further development of the software and did not include it in its new Edge browser for Windows 10. The company will support Silverlight in other browsers until 2021.

TIP OF THE WEEK Do you regularly need to note your car’s general location because of travel or local street-cleaning regulations? Plenty of third-party parking apps are available, but you can also mark the spot with tools built into your smartphone’s operating system.

Android users running the Google Now app can find their most recent parking spot saved with the app’s Parking Location card, which senses when a user gets out of a car after driving around. You do need to enable Google Now in the Google app and have “Driving” set as your customary mode of transportation. (To get to the Driving option, tap the three-lined More menu, select Customize, then select Everything Else and then “How do you usually get around.”)

If you do not use the Google app but have an iPhone with the Location Services feature turned on, open the Apple Maps app after parking the car and wait to see your current position appear on the screen as a blue dot. Tap the lowercase “i” in the bottom-right corner and choose Drop Pin to mark your spot for later reference. The Google Maps app for Android and iOS can also mark and save locations.