How to Repair Your Mac’s Disk Using Safe Mode, fsck, and More

By | April 7, 2022

There’s no need to panic if your Mac won’t start. Ignore the heart-wrenching feeling that fixing your computer will take a long time. macOS includes a few simple fixes that can help get things done right away.

You don’t need to take your machine to a service center for repair. Save your time and money by trying to fix it yourself. If you regularly back up with Time Machine, you will not lose much.

Let’s take a look at how to restart a Mac that refuses to start.

Before We Begin

These tips are for instances where your Mac refuses to boot. You may see a black screen, you may get an error message, or your computer may hang on a white Apple logo. If your machine is working fine, this troubleshooting guide is not for you.

You can, however, run First Aid on your drive at any time in macOS. If you suspect a problem with your startup drive is due to performance issues or erratic behavior, running First Aid should certainly be painless.

To run First Aid on your startup volume, launch Disk Utility and select Macintosh HD (assuming you haven’t renamed your startup volume). Click First Aid followed by Run to scan for problems and try to fix them.

Try Safe Mode

By attempting to boot into Safe mode, macOS will scan and repair any errors it finds on the disk. Safe mode boots your operating system with only the bare minimum needed to run it.

No third party kernel extensions will boot, login items are skipped, and it clears certain caches. Simply booting into safe mode, you’ll check for problems and get rid of any trash that might be causing them.

To boot into Safe mode: Shut down your computer, then press and hold the button Shift when your computer boots up. If your computer is stuck on boot, shut it down by holding down the power button until the machine shuts down (about 10 seconds) first.

If your computer boots up properly, try restarting and booting as usual. If your computer hangs again, try using Verbose mode by holding Cmd + V on startup and checks to see if a certain kernel extension is causing the problem. You can then restart into Safe mode, remove the problem extension, and try again.

Recovery Mode and First Aid

If Safe mode doesn’t fix your problem, Recovery mode is your next best bet. Every Mac ships with Recovery mode, which lives on a separate partition on the startup disk. This mode allows you to repair/restore your drive, access Terminal, and reinstall macOS.

To boot into Recovery mode: Shut down your computer, then press and hold Cmd + R when your computer boots up.

If you are having trouble booting into Recovery mode, it may be due to a problem with your drive, you can start recovery mode from the internet by holding down Cmd + Option + R As a replacement. Keep in mind this requires an internet connection and will take longer, as macOS will need to download the image first.

After booting into Recovery mode, you will see several options. Launch Utility Disk and then isolate the drive causing the problem – probably labeled Macintosh HD. Choose from the list on the left, then click First Aid followed by Run.

Use fsck in Single User Mode

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

Depending on the size of your volume, the type of drive you have installed, and potential problems, fsck can take a while to complete. Patience and persistence are essential if you want to repair your drive this way.

To run fsck, you must boot into Single User mode. This boot mode allows you to make changes to shared user resources. Single User Mode does not attempt to boot macOS; it only provides access to the Unix command line.

To boot into Single User mode: Shut down your computer, then press and hold Cmd + S when your computer boots. You will immediately see a command line prompt. You can type fsck -fy to run fsck.

Notes: If you have encrypted your drive, you will need to select the relevant user account and enter your password to decrypt it. If you set a firmware password on your Mac, Single User mode is not available to you.

It is important to wait for fsck to finish before you restart your computer again. If you stop the process while making changes to your drive, you may experience data loss. When the process is complete, you will see one of the following messages:

** The volume Macintosh HD could not be repaired.
*****The volume was modified *****

If you see this message, you must run fsck -fy again. There’s no harm in trying a few times, as the process makes changes to your drive with each pass.

** The volume Macintosh HD was repaired successfully.
*****The volume was modified *****

This is a more encouraging message, but you’re not done yet. Run fsck -fy again.

** The Macintosh HD volume appears to be OK.

This is what you want to see. fsck has checked the drive and made no changes.

When you get all-clear, it’s time to restart your Mac by running the command Exit.

Still Can’t Boot Your Mac

If you really want to try fixing the problem yourself, you should turn to Technician-level Apple Service Diagnostics to learn as much information as possible about the problem.

Recovering Files From Your Mac’s Corrupt Disk

If your disk is damaged beyond repair, there is a chance that you will lose some of your data. The first step to try is to create a drive image, to which you will need to connect a spare external drive that is at least as large as the startup disk you are trying to save.

Boot your Mac into Recovery mode with Cmd + R at startup, then run Disk Utility. In the menu bar at the top of the screen select File> New Image> Image from “Macintosh HD” (or whatever the name of your drive is).

Specify your external drive and start the process. This may take a while, and if the drive is damaged, it may even fail miserably. If the process is successful, you will create a DMG file of your old drive which you can mount and configure as you see fit.

Copying Files Manually

If that fails, you will have to copy your files manually. You can do this in Recovery mode, but you have to launch Terminal at startup instead of Disk Utility. To do so:

  • Connect the external drive you want to use as a destination for your files.
  • Restart your Mac in Recovery mode by holding down Cmd + R at startup, then select Terminal.
  • Use command cp -r to copy your files to an external drive. As an example: cp -r /Volumes/Macintosh HD/Users/[username]/Documents /Volumes/Backups/

Let’s break down the above command: cp is the copy command, and -r runs this command recursively. That means it will copy all the directories in the directory you specify, then the directories within, and so on.

The first path is the location of the file you want to copy. Notice the backslash () in the path name, which you use to specify a location that has a space in its name. The second path is the location of your external drive, which will always be at /Volumes/ with whatever label you provide (in the example above, the drive is called Backup).

The problem with this approach is that you have to remember where your files are. You also need to hope that they are not stored on a partially damaged drive. With your files safe, you can move on to repairing your Mac and reinstall macOS.

The Importance of Backing Up Your Mac

Hope you can recover your drive or any important files you may need. Even with a successful restore, and plenty of tools at your disposal, there’s nothing quite like the peace of mind a recent backup provides.