When simple measures such as restarting your Mac fail to make things right, you’ll probably need to call in Disk Utility’s First Aid tools. Here’s how to use them.
Launch Apple’s Disk Utility You’ll find Disk Utility in /Applications/Utilities. Click on the First Aid tab and select the name of the volume you want to fix from the list on the left side of the window (see “Patch Things Up”).
Turn on Journaling To make it easier for First Aid to do its job, make sure journaling is enabled for your disk volumes. The journaling feature (introduced in OS X 10.3) keeps track of changes to files on your drive. If a crash occurs, this helps the utility restore the drive to its previous, stable state.
If journaling is already enabled, the Enable Journaling button in the toolbar will be dimmed. If it’s not dimmed, click on the button. This won’t fix your current problem, but it’s a good preventative measure.
Verify or Repair? Disk Utility gives you two options: Verify and Repair. When you verify, the utility checks for problems but doesn’t make any repairs, even if problems are found. This can be useful if you’re not yet sure you want to risk modifying your disk (perhaps because you want a chance to back up your data first, just in case).
Patch Things Up Use Disk Utility’s First Aid tab to repair disk permissions or make more-general disk repairs. If the Repair Disk button is dimmed, as it is here, you’ve selected your startup volume. You need to reboot from your OS X DVD or an external FireWire drive to make repairs.
If you’re using OS X 10.4.3 (or later) and you think the problem is with your startup disk, you might also choose to verify. It’s annoying but true—you can’t repair a disk that you’re using. A new Live Verification feature, however, lets you verify even the startup volume, so you can see whether problems exist before you have to bother with rebooting from another volume or your OS X installation disk.
Live Verification works only for volumes with journaling enabled, which is another reason to enable it. Also, like any new fea-ture, Live Verification has some bugs. In particular, false error messages occasionally appear. For example, you can ignore an “Incorrect size for file temp” error message.
Choose Your Medicine Now decide whether you need to run Repair Disk Permissions or Repair Disk. They are quite different, so you may want to run both.
Repair Disk Permissions fixes faulty permissions settings for all files installed by OS X’s Installer utility. OS X uses Unix permissions settings to determine your read and write access to files. If programs or documents won’t open or are acting oddly, a permissions problem is often the culprit. You can repair disk permissions only on disks with OS X installed.
On the other hand, you can run Repair Disk on any volume, even one without OS X installed. This tool attempts to repair problems in a disk’s directory, which keeps track of where everything on the disk is stored. This kind of repair can fix almost any ailment, from an inability to open a document to a complete failure to start up.
If you selected Repair Disk, and Disk Utility claims to have found errors but fixed them, select Repair Disk again, just to make sure. If Disk Utility finds errors it can’t fix, you’ll need a more powerful repair utility, such as Alsoft’s DiskWarrior or Micromat’s TechTool Pro (see “The Mac Medicine Cabinet”).
If the Repair Disk Button Is Dimmed When you choose the current startup volume, the Repair Disk button will be dimmed. The easiest way to fix this problem is to insert the Tiger DVD (or the Tiger Install DVD that came with your Mac) and hold down the C key while your Mac starts up. This will make it boot from the system software on the DVD instead of the software on your hard drive. Select Disk Utility from the Utilities menu. Now you’ll be able to choose your regular startup volume from the list and click on Repair Disk.
[ Contributing Editor Ted Landau continues to search for new ways to get into and out of trouble. For more troubleshooting tips, see his book Ted Landau’s Mac OS X Help Line: Tiger Edition (Peachpit Press, 2006). ]