How do I repair system disk WITHOUT a CD?

in Genius Bar edited January 2014
So I heard a weird noise coming from the bottom left corner of my powerbook (12 inch, 1.33 GHz). It sounded like the top of a glass bottle clicking. Not a good noise. So immediately I opened disk utility and verified disk. After hanging for about 3 minutes, this is what it told me:

Verifying volume ?Macintosh HD?

Checking HFS Plus volume.

Checking Extents Overflow file.

Checking Catalog file.

Checking multi-linked files.

Checking Catalog hierarchy.


Checking Extended Attributes file.

Checking volume bitmap.

Checking volume information.

Volume Header needs minor repair

The volume Macintosh HD needs to be repaired.

Error: The underlying task reported failure on exit

1 HFS volume checked

\tVolume needs repair

OK, so hopefully its minor repair (**cross fingers**)

But my OS X install CD is at my parents house, in another city! How can I repair the disk without the CD? I'm afraid to use my laptop at all until I repair the disk.

Is there anything I should do in the meantime?

Thank you all, even if you're just reading and have no idea how to help me.


  • Reply 1 of 8
    chychchych Posts: 860member
    You can boot into single user mode and run fsck (file system check, same as disk utility check/repair disk). See this website:
  • Reply 2 of 8
    I had a look at the site and it's pretty intimidating. I'm not at all experienced in Unix or even Terminal, so I'm afraid of really messing things up.

    So basically, if I want to repair the disk, I start up in Single User Mode, and I'll be greeted with a prompt? Then I just type:

    sudo diskutil repairDisk /Volumes/Data

    Which should:

    Repair the file structure on the volume "Data" (note: this unmounts the volume during repair)?

    Is there any risk in doing this?
  • Reply 3 of 8
    chychchych Posts: 860member
    You basically start up in single user mode (hold cmd+s during startup).

    Use the command 'fsck' to repair your disks, by entering in:

    fsck -yf

    Then give it a while for it to check and repair the disk. If it says that the filesystem has been 'modified', run fsck again until it says 'Disk checked OK'. To get out, just type in 'reboot'. This shouldn't be dangerous, and your disks shouldn't be mounted at all in single user mode.
  • Reply 4 of 8
    kickahakickaha Posts: 8,760member
    And not mounted, means not writable.

    Just boot into single user mode, and you'll see a message that tells you to do two things: check disk with fsck, and mount the disk for use with mount. Just do the former. If it says it repaired an error, try it again, until it reports all AOK, then type 'boot' to continue the boot process. ('reboot' works as well, but 'boot' just continues from that point on - saves a few seconds. You can also hit Ctrl-D to 'log out' of single-user mode, and continue the boot process.)

    fsck is the underlying tool that Disk Utility uses, so this is *exactly* the same as running Disk Utility on your boot drive, except that you have the added safety of not being able to write to it accidentally, other than what fsck does.

    If at any point you get nervous, just enter the 'boot' command, and it'll continue as if you had rebooted normally. No harm, no foul.
  • Reply 5 of 8
    chychchych Posts: 860member
    I was under the impression that disks have to be unmounted for fsck to be able to write to the disk, as disk utility unmounts a disk when you run it's repair.
  • Reply 6 of 8
    kickahakickaha Posts: 8,760member
    Exactly. When you first boot into single-user mode, the main drive is *not* mounted. The message above the first prompt tells you to run fsck to check the drive, then mount it for continued use.

    Just do the first, skip the second, and you've checked your drive without the need for a boot CD.
  • Reply 7 of 8
  • Reply 8 of 8
    Or you could take out the drive and mount it in an additional machine

    I think fsck is a bit easier though
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