A: Properly repairing the macOS directory isn't quite as easy today as it was in previous systems, but still doable by the end user.
First, let's discover what is a directory.
We can think of a computer storage device (hard drive, flash drive, solid state drive, thumb drive, etc.) as the digital equivalent of a book. Data in a book is stored on pages, data in a storage device is stored on tracks - thin segments of magnetized area.
To locate data in a book, we typically refer to the table of contents. The table of contents for a storage device is its directory.
The directory can become corrupted in many ways–voltage surges and sags, static electric discharge between the user and computer, excessive temperature, physical shock, solar flare, and more. When the directory becomes damaged, the operating system may have problems finding a file, opening an application or file, or even booting.
macOS includes a utility to diagnose and repair most directory damage–Disk Utility. It is located in the Boot Drive / Utilities folder. However, using Disk Utility while booted into your computer may not repair all of the directory damage. This is akin to a doctor performing brain surgery on herself. At some point, things go dark for both patient and doctor!
In previous versions of the system, Disk Utility could only scan for directory problems while booted, without the option to repair. To perform a repair required booting from another drive.
In current versions of macOS, although Disk Utility can perform some repair while booted, a bit more work is needed for full repair. To do this:
- Power off the Mac.
- Power on the Mac.
- Immediately (within a half second or so), press and hold down the option + command + R keys. This will boot the computer into Internet Recovery mode, not the normal operating system. Continue holding the keys until you see an Apple logo center screen.
- At the utilities window, select Disk Utility. Disk Utility opens.
- In the sidebar, select your normal boot drive.
- If the boot drive name is grey, from the toolbar (not menu bar), select Mount, and then enter your username and password.
- From the toolbar, select the First Aid button.
- At the Would you like to run First Aid prompt, select Run.
- When diagnostics and repairs complete, select the Done button.
- From the Apple menu, select Restart. Your computer will restart.
- Log in as normal.
The next question is when should directory repair be performed? There is no best practices provided by Apple, but my recommendation is:
- Once a month as routine maintenance.
- As the second step whenever your computer is running poorly. The first step being a power-cycle (Apple menu > Shut Down, wait a minute, power on and log in).