After my Open Firmware tip last week several patients wrote in about starting up in Single User Mode or Verbose mode. But, before I explain, I'd like to mention that several patients said that Open Firmware tip was "just the ticket," and that it cured a nagging ailment for them. Only one or two of you reported failure, and nobody reported ill effects. So I think it's a keeper.

Anyway, several patients asked if I knew any other startup tricks for OS X and I realized that I do but you might not. So here is the most important one of all (followed by one that's more or less a stupid Mac OS X trick to me...).

Single User Startup and File System Check (fsck)

This one is a must-know - if you don't know about it, here it is. I do this every time I have a freeze or crash, just in case. Running fsck is similar to running Disk Utility's First Aid, only better. First, it doesn't require a CD, so it's faster than the Disk Utility way. Second, when it's done running, you don't have to reboot if you know the magic word (hint: it's "exit.")

Any time you think your Mac isn't acting quite right, give it a try. Disk Utility and fsck are supposed to do the same exact thing, but there are times when fsck may be preferred. For example:

• Your CD-ROM drive is broken or otherwise unavailable.
• Your Mac OS X Install CD is not handy.
• You are a UNIX hound, and you like the command line.

Apple implies that Disk Utility runs the same tests and repairs disks the same way as fsck. But my experience has been different. Several times in the past few months, Disk Utility has given my hard disk a clean bill of health, but when I ran fsck immediately thereafter, it found and repaired multiple issues. So I prefer to run it first, then Disk Utility if necessary.

Apple says you should run the Disk Utility application on the Mac OS X CD before fsck, but I am going to go against the grain by stating that I believe your chance of success is greater if you run fsck first.

To run fsck, you first need to start up your Mac in single-user mode. Here's how:

• 1. Restart your Mac.
• 2. Immediately press and hold the Command and "S" keys.

You'll see a bunch of text begin scrolling on your screen. In a few more seconds, you'll see the Unix command line prompt (#). Congratulations. You're now in single-user mode. I bet you've never seen your Mac screen look like that before. (I wish I could show you a screen shot of it, but as far as I can tell, it's not possible. And photos of it are ugly.)

Now that you're at the # prompt, here's how to run fsck:

• 1. Type: "fsck - - y" (that's fsck-space-minus-y).
• 2. Press Return.

The fsck utility will blast some text onto your screen. If there's damage to your disk, you'll see a message that says:

***** FILE SYSTEM WAS MODIFIED *****

If you see this message--and this is extremely important--repeat Steps 1 and 2 again and again until that message no longer appears. It is normal to have to run fsck more than once -- the first run's repairs often uncover additional problems..

When fsck finally reports that no problems were found, and the # prompt reappears:

• 3. Type: "reboot" to restart,
• or type "exit" to start up without rebooting.
• 4. Press Return.

Your Mac should proceed to start up normally to the login window or the Finder.

Note that the above passage was copied and pasted directly from Chapter 8 of my latest book, Dr. Mac: The OS X Files, with my express permission. I hate to type the same thing twice.

Anyway, that second tip? It's called Verbose Mode and it makes your Mac flow a bunch of that lovely UNIX text across your screen before jumping to Aqua and revealing its GUI... This one's fun to do in front of Mac users unfamiliar with OS X. Hold down Command-V during startup. As soon as you see white text on a black background, you can release the keys. After a few minutes of spewing text, your Mac will all of a sudden grow a colorful user interface. It's wacky. I can't tell much from the words but I would bet UNIX gurus could tell you what it's all about. If you care. As for me, I know enough about it to be dangerous and that's enough for me.

To discuss this tip (or anything you like) in Dr. Mac's OSXFAQ Forum, click Here:

Bob LeVitus is a leading authority on Mac OS and the author of 39 books, including Mac OS X For Dummies and The Little iTunes Book.