Disk Utility says that you can’t repair your boot volume because your Mac can’t be booted – or running – from the internal hard drive at the same time it needs to be repaired. It’s like trying to do a tune up on the engine of a car while it’s still running; it’s not good for the engine, and you might catch your fingers in the fan or burn them on the exhaust manifold.
OS X needs to have all of the files on the hard drive to be repaired to not be in use at the time the the disk is repaired. Think of trying to change a spark plug while the engine is running – at very least you’re going to get a shock. With OS X, if a file is in use by the operating system and the permissions are changed on it, more than likely OS X will crash or your Mac will freeze up or file damage can occur.
Boot from the DVD or the CD that came with your Mac. They are the software install discs, but they also have other utilities on them, such as Disk Utility, and an administrator password reset utility.
This is the way to start up your Mac from a DVD of CD from the Apple Knowledge Base:
1 – Insert the Mac OS X Install disc that came with your computer, then restart the computer while holding the C key.
2 – When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3 – Click the First Aid tab.
4 – Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5 – Select your Mac OS X volume.
6 – Click Repair. Disk Utility checks and repairs the disk.
When booting from a DVD or CD, your Mac will take a longer to start up because optical media is slower than hard drives, but give it a few minutes to grind away.
Using the repair features of Diak Utility are different than repairing or verifying disk permissions. if you want to repair permisisons, Apple recommends doing that without starting up from a different disk or installer CD or DVD, according to this article “About Disk Utility’s Repair Disk Permissions feature:”
When possible, disk permissions should be repaired while started up from a Mac OS X volume (hard disk) that contains updated Mac OS X software, instead of a Mac OS X installation disc. Mac OS X software updates may change permissions on some files to improve security. When this occurs, the version of Disk Utility on the Mac OS X volume is updated to account for the new permissions. Running Disk Utility while started from the Mac OS X volume ensures that the changes made by software updates are preserved.
Another article in the Apple Knowledge Base is Troubleshooting permissions issues in Mac OS X. This gives a good run down on what file permissions are, how they should be set by default and how they are repaired.
Disk Utility can do more than verify and repair disk file permissions and fix other disk problems. You can burn CDs with disk utility, though it can be faster and you have more options if you use other CD burners, such as Roxio’s Toast.
Just drag your files onto the icon of a blank CD you have in the drive, and then open the Finder window. You’ll see a “burn” button in the menu bar. If you happen to try to eject the CD without burning the files, you’ll be asked if you want to burn the disk.
Disk Utility can also make images of disks and burn Windows CDs, too. The Apple Knowledge Base article isMac OS X: About burning data onto CDs