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Note: this article is taken from MAC OS X Tiger: The Missing Manual Copyright © 2005 Pogue Press, LLC. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media, www.oreilly.com.
Not every problem you encounter is related to running applications. Sometimes trouble strikes before you even get that far. The following are examples.
When you see the cheerful, multilingual dialog box shown in Figure B-2, you've got yourself a kernel panic—a Unix nervous breakdown.
(In such situations, user panic might be the more applicable term, but that's programmers for you.)
Figure B-2. A kernel panic is almost always related to some piece of add-on hardware. And look at the bright side: At least you get this handsome dialog box in Tiger. That's a lot better than the Mac OS X 10.0 and 10.1 effectrandom text gibberish super-imposing itself on your screen.
Kernel panics are increasingly rare. If you see one at all, it's almost always the result of a hardware glitch—most often a bad memory (RAM) board, but possibly an accelerator card, graphics card, SCSI gadget, or USB hub that Mac OS X doesn't like. A poorly seated AirPort card can bring on a kernel panic, too, and so can a bad USB or FireWire cable.
If simply restarting the machine doesn't help, detach every shred of gear that didn't come from Apple. Restore these components to the Mac one at a time until you find out which one was causing Mac OS X's bad hair day. If you're able to pinpoint the culprit, seek its manufacturer (or its Web site) on a quest for updated drivers, or at least try to find out for sure whether the add-on is compatible with Mac OS X.
There's one other cause for kernel panics, by the way, and that's moving, renaming, or changing the access permissions for Mac OS X's essential system files and folders—the Applications or System folder, for example. (See Section 12.10 for more on permissions.) This cause isn't even worth mentioning, of course, because nobody would be that foolish.
Safe Mode (Safe Boot)
In times of troubleshooting, Mac OS 9 fans press the Shift key at startup to turn off the extensions. Windows fans press an F-key to start up in Safe Mode. Either way, the idea is the same: to turn off all nonessential system-software nubbins in an effort to get a sick machine at least powered up.
Although not one person in a hundred knows it, Mac OS X offers the same kind of emergency keystroke. It can come in handy when you've just installed some new piece of software and find that you can't even start up the machine, or when one of your fonts is corrupted, or when something you've designated as a Login Item turns out to be gumming up the works. With this trick, you can at least turn on the computer so that you can uninstall the cranky program.
The trick is to press the Shift key as the machine is starting up. Hold it down from the startup chime until you see the words "Safe Boot," in red lettering, on the login screen.
Welcome to Safe Mode.
What have you accomplished?
Once you reach the desktop, you'll find a long list of standard features inoperable. You can't use DVD Player, capture video in iMovie, use a wireless network, use certain microphones and speakers, or use your modem. (The next time you restart, all of this goodness will be restored, assuming you're no longer clutching the Shift key in a sweaty panic.)
In any case, the beauty of Safe Mode is that it lets you get your Mac going. You have access to your files, so at least the emergency of crashing-on-startup is over. And you can start picking through your fonts and login items to see if you can spot the problem.
Gray Screen During Startup
Confirm that your Mac has the latest firmware, as described earlier. Detach and test all your non-Apple add-ons. Finally, perform a disk check (see below).
Blue Screen During Startup
Most of the troubleshooting steps for this problem (which is usually accompanied by the Spinning Beachball of Death cursor) are the same as those described under "Kernel Panic" above. But there's one other cause to examine: a corrupted font file in your Mac OS 9 System Folder.
To test for this problem, restart the Mac in Mac OS 9 (if your Mac can do that), open its System Folder (that's the folder called System Folder, not just System), and drag the Fonts folder to the desktop. Restart in Mac OS X. If the startup proceeds smoothly, you know you've got a damaged font file in that Fonts folder.
If you or one of the other people who use your Mac have forgotten the corresponding account password, no worries: Just read the box on Section 12.5.
Fixing the Disk
The beauty of Mac OS X's design is that the operating system itself is frozen in its perfect, pristine state, impervious to conflicting system extensions, clueless Mac users, and other sources of disaster.
That's the theory, anyway. But what happens if something goes wrong with the complex software that operates the hard drive itself?
Fortunately, Mac OS X comes with its own disk-repair program. In the familiar Mac universe of icons and menus, it takes the form of a program in Applications→Utilities called Disk Utility. In the barren world of Terminal and the command line interface, there's a utility that works just as well but bears a different name: fsck (for file system check).
In any case, running Disk Utility or its alter ego fsck is a powerful and useful troubleshooting tool that can cure all kinds of strange ills, including these problems, among others:
The easiest way to check your disk is to use the Disk Utility program. Use this method if your Mac can, indeed, start up. (See Method 2 if you can't even get that far.)
Disk Utility can't check the disk it's on (except for permissions checks, described at the beginning of this appendix). That's why you have to restart the computer from the Tiger installation disc (or another startup disk), and run Disk Utility from there. The process goes like this:
If you see the message, "The volume 'Macintosh HD' appears to be OK," that's meant to be good news. Believe it or not, that cautious statement is as definitive an affirmation as Disk Utility is capable of making about the health of your disk.
Disk Utility may also tell you that the disk is damaged, but that it can't help you. In that case, you need a more heavy-duty disk-repair program like Drive 10 (www.micromat.com) or DiskWarrior (www.alsoft.com).
Method 2: fsck at the Console
Disk Utility isn't of much use when you can't find the Tiger DVD, when your CD drive isn't working, or when you're in a hurry to get past the startup problems that are plaguing your machine. In these cases, you'll be glad that you can boot into the Mac's raw Unix underlayer to perform some diagnostic (and healing) commands.
Specifically, you'll be glad that you can run the Unix program fsck, for which Disk Utility is little more than a pretty faceplate.
Like any Unix program, fsck runs at the command line. You launch it from the alltext, black Unix screen by typing fsck and pressing Enter. (As discussed in the box on the facing page, you can also use fsck -f.)
You can't, however, just run fsck in Terminal. You have to run it when the usual arsenal of graphic-interface programs—like the Finder and its invisible suite of accessory programs—isn't running.
Figure B-3. In console mode, your entire screen is a command line interface. Unix jockeys can go to town here. Everyone else can timidly type fsck -y after the localhost:/root # promptsee this prompt on the very last line?and hope for the best.
Single-user mode (⌘-S at startup)
The Terminal program is the best known form of Mac OS X's command line, but it's not the only one. In fact, there are several other ways to get there.
In general, you don't hear them mentioned except in the context of troubleshooting, because the Terminal program offers many more convenient features for doing the same thing. And because it's contained in a Mac OS X–style window, Terminal is not so disorienting as the three methods you're about to read.
All of these techniques take you into console mode, shown in Figure B-3. In console mode, Unix takes over your screen completely, showing white type against black, no windows or icons in sight. Abandon the mouse, all ye who enter here; in console mode, you can't do anything but type commands.
To get there in times of startup troubleshooting, press ⌘-S while the Mac is starting up. (If you're stuck at the frozen remnants of a previous startup attempt, you may first have to force-restart your Mac; see the tip on Section B.4.)
Instead of arriving at the usual desktop, you see technical-looking text scrolling up a black screen as the Mac runs its various startup routines. When it finally stops at the localhost # prompt, you're ready to type commands. You're now in what's called single-user mode, meaning that the Unix multiple-accounts software has yet to load. You won't be asked to log in.
At the localhost # prompt, type fsck -y (note the space before the hyphen) and press Enter. (They means "yes," as in "yes, I want you to fix any problems automatically.") If the Mac refuses because journaling is turned on (Section B.8.5), you can also type fsck-fy to force the disk check.
Now the file system check program takes over, running through five sets of tests. When it's complete, you'll see one of two messages:
Where to Get Troubleshooting Help
If the basic steps described in this chapter haven't helped, the universe is crawling with additional help sources.
These Web sites contain nothing but troubleshooting discussions, tools, and help:
Help by Telephone
Finally, consider contacting whoever sold you the component that's making your life miserable: the printer company, scanner company, software company, or whatever.
If it's a Mac OS problem, you can call Apple at 800-275-2273 (that's 800-APL-CARE). For the first 90 days following your purchase of Mac OS X (which, as far as Apple knows, is the date of your first call), the technicians will answer your questions for free.
After that, unless you've paid for AppleCare for your Mac (a three-year extended warranty program), Apple will charge you to answer your questions. Fortunately, if the problem turns out to be Apple's fault, they won't charge you.