How to Repair a Mac Disk with fsck from Single User Mode

Aug 7, 2013 - 9 Comments

Using Disk Utility through Recovery Mode is the preferred and primary tool for repairing disks on the Mac platform, but if Disk Utility is either unavailable or not able to repair a drive, then Single User Mode and the command line tool fsck should be your next choice.


The fsck tool is bundled with every Mac, but because it’s accessible exclusively through the command line it may appear complex and sound more intimidating than it really is. Fear not though, because using fsck is actually quite simple, and there are several cases where it can repair a problem with a drive that Disk Utility was unable to.

How to use Single User Mode and fsck to repair a disk

  • Boot the Mac into Single User Mode by holding down Command+S during system boot after you hear the boot chime, you know you will have successfully entered Single User Mode because you will see a bunch of white text on a black background scroll by
  • When the Single User boot sequence has finished, you’ll find a small command prompt at the bottom of the screen prefixed by a hash sign (#), when you see that type the following command exactly:
  • fsck -fy

  • Once fsck completes, if you see a “File system was modified” message, then you should run “fsck -fy” again until you see a message stating “The volume (name) appears to be OK” – this is standard procedure of using fsck
  • Type “reboot” to leave Single User Mode and boot the Mac back into OS X as usual

Once OS X is booted again, it can be a good idea to confirm all is well by going back to Disk Utility and running the “Verify” tool to check on the drives health.

Keep in mind that if the ‘fsck’ tool continuously fails or reports errors and Disk Utility is a no go as well, the hard drive itself very well may be failing and on its last legs, so be sure to initiate a back up all of your critical data using Time Machine or your backup method of choice, and aim to get the drive replaced sooner than later.

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Posted by: Paul Horowitz in Command Line, Mac OS X, Tips & Tricks


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  1. jeniffer brolaney says:

    amazing!! thank you sooo much! i was so mad cuz i bought a used macbook from a private seller and she/he left it logged in. i couldnt download anything. i couldnt change anythiny. for heavens sake i couldnt even get in! anyways thanks! haha(:

  2. Dimitris says:

    That was easy. The Mac is telling you that once in S.U. Mode!
    The trick is how you find the partitions (names) you might have and fsck them.

  3. Mikko says:

    This was a splendid advice. I used it for a Yosemite system disk.
    The first run of fsck was disappointing:
    ** The volume Macintosh HD could not be repaired.
    *****The volume was modified *****
    But the second run was very promising:
    ** The volume Macintosh HD was repaired successfully.
    *****The volume was modified *****
    And the third run confirmed
    ** The volume Macintosh HD appears to be OK.
    Thank you very much!

  4. Himadri says:

    Thanks a ton…!!!

    This was really an excellent approach… worked for me on my Macbook Pro HD with lately upgraded to OS X Yosemite…I tried to fix the issue using Disk Utility, but it failed to repair the disk…Then I tried with ‘fsck -fy’ and the first time it showed it’s charm….!!!

  5. Allan Ferreira says:

    Fixed!!! Thanks

  6. olka says:

    Thanks, saved my day!

  7. Khnz says:

    Hi mate

    Can you help me out with my MacBook Pro? I try to boot fsck on my mac according to your suggestion when it failed to show the HDD. When I put fsck in, it said command not found. What should I do?
    Thank you

  8. Feno1 says:

    sbin/fsck -fy absolutely worked for me on MB Pro. Well done and thanks for sharing.

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