In Mac OS X, what is First Aid, and when and how should I use it?

What is First Aid?

First Aid is a utility included in Mac OS X for checking and repairing file system errors. It is part of the Disk Utility program.

When should I use First Aid?

If your computer is crashing frequently, displaying cryptic error messages, or exhibiting unusual behavior, you can use First Aid as a first step to check for defects and, in many cases, repair them. If, however, your volume has suffered severe corruption, you may need to use other utility programs or repair methods.

Even if you are not getting errors, it is a good idea to run First Aid periodically. This preventive maintenance will help keep small problems from developing into bigger ones.

How do I run First Aid?

Note: For help with correcting permissions problems rather than file system errors, see Using Mac OS X, how do I repair permissions, and what does that do?

To check your startup disk, you must run First Aid from your software installation CD or DVD. Insert the disc, restart your computer, and hold the  c  key down while restarting to force your computer to boot from the CD or DVD. Follow the instructions on the screen, and when the menu bar appears, from the Utilities (Mac OS X 10.5), Disk Utilities (Mac OS X 10.4), or Installer (Mac OS X 10.3) menu, select Disk Utility. In the column on the left, select the volume you want to repair, and then on the right, click the First Aid tab. You may select multiple volumes by holding down the Cmd key while clicking the volumes.

Click Verify Disk to begin a verification process (a simple check for errors), or Repair Disk to verify and repair any problems on the selected volume(s). You can stop the scan at any time by clicking Stop Verify or Stop Repair.

Disk First Aid results

The results of a verification and/or repair will be posted in the window. You should run First Aid repeatedly until you see the following message at the end of the scan, where diskname is the name of your disk:

"The volume "diskname" appears to be OK."

Note: Some volumes can be verified but not repaired. For example, the startup disk, the volume where Disk Utility resides, a write-protected disk (such as a CD-ROM or a locked floppy), or a disk that has open files can all be verified, but not repaired. Disk First Aid will warn you if one of these conditions exists when you select a volume.

What if First Aid found problems it cannot repair?

Occasionally, at the end of a scan, a message similar to the following will appear:

"Scan complete. Problems were found, but Disk First Aid cannot repair them."

This indicates that some of your files may be more severely damaged. To repair this damage, you can either back up your disk and reformat, or obtain a more comprehensive disk repair program. Two such programs are DiskWarrior from Alsoft, and TechTool Pro from Micromat Computer Systems.

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