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