Mac OS X References for Restart

1. Try Safe Mode

To boot into Safe mode: Turn your computer off, then press and hold the Shift key while your computer boots. If your computer has hung on boot, shut it down by holding the power button until the machine switches off (around 10 seconds) first.

2. Recovery Mode and First Aid

To boot into Recovery mode: Turn your computer off, then press and hold Cmd + R while your computer boots.

If you have trouble booting into Recovery mode, perhaps due to problem with your drive, you can start recovery mode from the internet by holding Cmd + Option + R instead. Keep in mind this requires an internet connection and will take a lot longer, since macOS needs to download the image first.

Once you’ve booted into Recovery mode, you’ll see a few options. Launch Disk Utility and then isolate the drive that’s causing problems—it’s probably labeled Macintosh HD. Select it from the list on the left, then click First Aid followed by Run.

3. Use fsck in Single User Mode

File system consistency check (or fsck for short) is a longstanding Unix tool for checking and fixing drive problems.

Depending on the size of your volume, the type of drive you have installed, and the potential problem, fsck can take a while to complete. Patience and persistence is important if you want to fix your drive this way.

To run fsck, you’ll need to boot into Single User mode. This boot mode allows you to make changes to shared user resources. Single User mode doesn’t attempt to boot macOS; it only provides access to a Unix command line.

To boot into Single User mode: Turn your computer off, then press and hold Cmd + Swhen your computer boots. You’ll soon see a command line prompt. You can type fsck -fy to run fsck.