If your Mac is only displaying the blue screen when you start up, or you can log in but the desktop fails to appear, you may have a problem with your startup drive. The usual course of action is to run Disk Utility to attempt to repair the startup drive, but you can't do that if your Mac doesn't start, right? Well, here's what you can do.
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When a Mac fails to start up normally, one of the common troubleshooting practices is to verify and repair the startup drive. A startup drive that is experiencing problems is likely to prevent your Mac from starting, so you may find yourself in a catch 22. You need to run Disk Utility’s First Aid tools, but you can’t get to Disk Utility because your Mac won’t start.
There are three methods of getting around this problem.
- Booting from a different device: This can be another drive that has a bootable system on it, or your OS X Install DVD, which also contains the Disk Utility tools or the Recovery HD which is a special partition on your startup drive that has been present since OS X Lion and later.
- Safe Mode: This is a special booting method that forces your Mac to perform an automatic disk check and repair as it tries to start up.
- Single User Mode (fsck): This is another special startup method that allows you to run command line utilities, such as fsck, which can verify and repair hard drives.
Boot From Alternate Device
The easiest solution by far is to boot from a different device. The three most popular options are another bootable startup drive, an emergency startup device, such as a bootable USB flash device, or a current OS X Install DVD.
To boot from another hard drive or a USB flash device, hold down the option key and start up your Mac. The Mac OS startup manager will appear, allowing you to select the device to boot from.
To boot from your OS X Install DVD, insert the DVD into your Mac, and then restart your Mac while holding down the letter c key.
To boot from the Recovery HD, restart your Mac while holding down the command (cloverleaf) and R keys (command+r).
Once your Mac finishes booting, use Disk Utility’s First Aid feature to verify and repair your hard drive.
Boot Using Safe Mode
To start up in Safe Mode, hold down the shift key and then start your Mac. Safe Mode takes a while, so don’t be alarmed when you don’t see the desktop right away. While you’re waiting, the operating system is verifying the directory structure of your startup volume, and repairing it, if necessary. It will also delete some of the startup caches that may also be preventing your Mac from starting successfully.
Once the desktop appears, you can access and run Disk Utility’s First Aid tool just as you normally would. When First Aid is finished, restart your Mac normally.
Please note that not all applications and OS X features will work when you boot into Safe Mode. You should use this startup mode only for troubleshooting and not for running day-to-day applications.
Boot Into Single User Mode
Start your Mac and immediately hold down the command key plus the letter s key (command+s). Your Mac will start up in a special environment that looks like an old-fashioned command line interface (because that’s exactly what it is).
At the command line prompt, type the following:
Press return or enter after you type the above line. Fsck will start and display status messages about your startup disk. When it finally finishes (this can take a while), you will see one of two messages. The first indicates that no problems were found.
The second message indicates that problems were encountered and fsck attempted to correct the errors on your hard drive.
If you see the second message, you should repeat the fsck command again. Continue to repeat the command until you see the “volume xxx appears to be OK” message.
If you don’t see the volume OK message after five or more attempts, your hard drive has serious problems that it may not be able to recover from.
I'm trying to recover an apparently corrupted disk. It appears that through improper shutdown the drive has been somehow killed. It's the main partition of a Macbook Pro.
I've used dd to copy the drive to an external hard drive, and now I'm trying to mount it under linux (Ubuntu) to retrieve whatever I can. (I can also try from another Mac.)
Info on the disk image from file image.dmg
image.dmg: Macintosh HFS Extended version 4 data (mounted) last mounted by: 'FSK!', created: Wed Nov 18 08:21:40 2144, last modified: Mon Mar 6 18:54:12 2147, block size: 4096, number of blocks: 121886744, free blocks: 69886793
Trying mount -t hfsplus -o loop image.dmg /mnt resulted in
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
from dmesg
hfsplus: Filesystem was not cleanly unmounted, running fsck.hfsplus is recommended. mounting read-only.
hfsplus: invalid extent max_key_len 53348
hfsplus: failed to load extents file
running fsck.hfsplus -dr image.dmg yields
** image.dmg (NO WRITE)
Using cacheBlockSize=32K cacheTotalBlock=1024 cacheSize=32768K.
CheckForClean - found bad journal signature
Invalid Volume Header
** Checking HFS Plus volume.
Invalid B-tree node size
(3, 0)
** The volume needs to be repaired.
volume type is pure HFS+
primary MDB is at block 0 0x00
alternate MDB is at block 0 0x00
primary VHB is at block 2 0x02
alternate VHB is at block 975093950 0x3a1ec0be
sector size = 512 0x200
VolumeObject flags = 0x07
total sectors for volume = 975093952 0x3a1ec0c0
total sectors for embedded volume = 0 0x00
Something is wrong with the superblock or with the B-node tree. I've seen recommendations for DiskWarrior out there, but I it has a high price for no guarantee that it will work, so I thought I'd try my hand at it with free approaches first.
Any any any (useful) info would be greatly appreciated! Thanks!
3 Answers
In the end DiskWarrior worked... it took several iterations of repair, but it managed to restore the node list enough for me to mount it and transfer off as much as was salvageable (which wasn't everything). Then I reinstalled through the usual OSX reinstallation. Thanks for the tips.
If you've a Firewire port and access to another Mac (also with a Firewire port) you may be able to mount your disk on the other Mac using Target Disk Mode, depending on how seriously hosed your drive is.
It may just be a case of corrupted system files preventing startup and it's entirely possible your drive will be accessible once it's mounted on another machine.
Try the disk repair from Disk Utility In the recovery partition, or install DVD.
Mac Dd Tool For Corrupt Dvd Soft
I read that the Linux hfs driver has not been updated for the latest OSX, so test a known working partition first.
Mac Dd Tool For Corrupt Dvd Styler
Assuming you did not enable drive encryption you can pull files off the img without mounting it with dd or smarter tools, alt list.
simple txt dd example;
If the drive was encrypted (new os x only) there will be no text at all in the img.
Be sure to check SMART data before using the disk again