What to do if Disk Utility can’t fix things

2 March 2016, 07:45


There are few worse error messages to see on your Mac than this one:

Error: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

It could appear when you’re using Disk Utility in a bid to try and fix a problem, and Disk Utility has simply shrugged its shoulders and given up.

Perhaps surprisingly, all is not necessarily lost. You might indeed need to wipe and reinstall but before that you can at least try a few other tricks.

Backup now!
Before attempting anything, however, you should backup your disk contents because it’s clear there’s a potentially huge issue and you’re living on borrowed time. If you haven’t already got one, beg, borrow or steal an external hard disk of sufficient size and attach it by USB, FireWire, Thunderbolt or Wi-Fi. Then use Time Machine, the OS X built-in backup software. Note that Time Machine only works with a handful of NAS – check the manual.

When the disk is attached Time Machine should detect it but if not open System Preferences, click Time Machine, and move the large switch to the On position. Then follow the instructions.

If you don’t fancy using Time Machine, apps like Carbon Copy Cloner will do a similarly good job.

Attempting a last-ditch repair
Reboot your Mac and, before the Apple logo appears, hold down Cmd+S. Release when the boot progress indicator appears. This will boot you into Single User mode and things will suddenly go very Linux, with a text-based display, as shown above. Don’t panic! Just wait until the flashing text cursor appears and type the following:

/sbin/fsck -fyd

If you see the following message at the end of the repair:

***** FILE SYSTEM WAS MODIFIED *****

… then type the command again. Repeat another two or three times until you have a message similar to this returned:

** The volume appears to be OK

Of course, you may never see this because even this trick might not be able to fix your disk. However, you might be able to make note of its output and google it to see if you can find a solution.

When you’ve finished in Single User Mode, type the following to reboot:

reboot

Note that you might not be able to enter Single User Mode if you have a firmware password set. You’ll need to temporarily disable it. Additionally, on a Retina display the text will be tiny – but still readable if you move closer to the screen!

Commercial rescue apps
You might want to try some of the commercial disk repairing apps like TechTool Pro but the quickest solution might be to do as Disk Utility suggests, which is to wipe the disk, and restore from a backup – or wipe the disk and reinstall OS X. Both options are available within OS X Recovery, accessible by holding down Cmd+R while booting your Mac.


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Leave a comment...

No Disk Warrior?

— Peter Gilbert · Mar 2, 02:16 PM · #

My mac was hanging on boot (progress bar would stop, then screen would go black).

Tried SMC/PRAM reset, booted into Recovery mode too and after opening disk utility and running the verification step it told me that the disk needed to be repaired. However, after running ‘disk repair’, I got an error that told me the disk couldn’t be repaired.

Anyway, booted into single-user mode and running the “last-ditch” fsck worked!

Thanks for the advice

— JJ · May 28, 11:33 AM · #

Hi all,
I’ve been experiencing some trouble with my MBP early 2011, running on Mavericks, but last night it completely gave up and is beyond repair by Disk utility, as I tried many advices from the web. There is clear a serious issue with HD so my last ditch effort was the fsck -fyd command on single mode. However, after 6hours I still don’t get the blinking cursor enabling me to type the command… I know I have to be patiente but I started to think over 6 hours is quite long.
As I’m no expert on this I started to think it is repeating the command over and over and they are basically:

hfs_mountfs: hfs_mountfs returned 22, rvp (0xffffff8038ba5f00) name (unknow device)
Cannot mount root, errno = 19

Bsd root: Disk 0s2, major 1, minor 3
Hfs: open_journal_device
?UMñ not found. Waiting 10sec.

hfs_mountfs: hfs_early_journal_init indicated external jnl

I’ve tried the single mode twice, the first time due to low bat it shut down, my bad, so I’ve agian with the power on and it is over 6 hours…
I’m tempted to stop it but I’m afraid to cause a greater damage on an already bad HD.
Please help…Thanks.

— Andrea · Aug 19, 06:04 AM · #

 
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