Resolve startup issues and perform disk

About live verification in Mac OS X 10.4.3 or later

In Mac OS X 10.4.3 or later, you can verify your startup disk while your Mac is started from it. This is known as live verification, and can be used in three different ways.

Option 1: Verify your disk using Disk Utility while started from the startup disk. To find out how to do this, see this article. Please note that live verification does not involve any disk repair, so if verification finds something that should be repaired, start up from your Mac OS X Install disc and use Disk Utility as described above in "Try Disk Utility."

Option 2 (advanced): Use the command line and the command-line utility, diskutil.

Note: Don't use this method to check non-startup volumes.

You should see messages such as the following during the disk check:

Could not unmount disk for verification, attempting live verify

Started verify/repair on volume disk0s3 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.

The volume Macintosh HD appears to be OK.

Mounting Disk

Verify/repair finished on volume disk0s3 Macintosh HD

Option 3 (advanced): Use the command line and the command.

Start up your computer and log in as an administrator.

Open Terminal (/Applications/Utilities).

At the prompt, type the following command and then press Return to determine your filesytem ID:

Look for lines of text that look like this:

Make a note of the first "disk" name that appears after /dev/, such as "disk0s3." This is your filesystem ID for your startup volume.

At the prompt, type the following command and then press Return:

Then type the following command, where "disk0s3" is your filesystem ID you noted in step 4, then press Return:

When prompted, enter your admin password, then press Return to begin the verification.

You should see messages like these during the disk check:

Advanced information

If you're interested in UNIX-style command-line syntax, here's a look at how a couple of flags used above can influence fsck:

The -y flag: Tells fsck that you want to answer "yes" to all questions about fixing, repairing, or salvaging information. This is the optimal approach, as answering "no" to any question causes fsck to stop. You cannot determine that all necessary repairs have been made until fsck completes and gives its final report.

The -f flag: Forces fsck to check filesystems that are marked as "clean".