B.9. Fixing the Disk

B.8. Startup Problems

Not every problem you encounter is related to running applications. Sometimes trouble strikes before you even get that far. The following are examples.

B.8.1. Kernel Panic

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 effect ”random 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.

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Tip: This advice goes for your Macintosh itself. Apple periodically updates the Mac's own "drivers" in the form of a firmware update . You download these updaters from the Support area of Apple's Web site (if indeed Mac OS X's own Software Update mechanism doesn't alert you to its existence).

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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.

B.8.2. 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?

• Checked your hard drive . The Shift-key business makes the startup process seem to take a very long time; behind that implacable Apple logo, Tiger is actually scanning your entire hard drive for problems. It's running the same disk check that's described on Section B.9.1.

• Brought up the login screen . When you do a safe boot, you must click your name and enter your password, even if you normally have Automatic Login turned on.

• Turned off your kernel extensions . All kinds of software nuggets load during the startup process. Some of them, you choose yourself (icons you add to the Login Items list in the System Preferences Accounts pane). Others, you don't normally see: a large mass of kernel extensions , which are chunks of software that add various features to the basic operating system. (Apple's kernel extensions in your System Library Extensions folder; others may be in your Library StartupItems folder.)

  If you're experiencing startup crashes, some non-Apple installer may have given you a kernel extension that doesn't care for Mac OS X 10.4 ”so in Safe Mode, they're all turned off.

• Turned off your fonts . Corrupted fonts are a chronic source of trouble ”and because you can't tell by looking, they're darned difficult to diagnose. So just to make sure you can at least get into your computer, Safe Mode turns them all off (except the authorized, Apple-sanctioned ones that it actually needs to run, which are in your System Library Fonts folder).

• Trashed your font cache . The font cache is a speed trick. Mac OS X stores the visual information for each of your fonts on the hard drive, so that the system won't have to read in every single typeface off of your hard drive when you open your Font menus or the Font panel.

  When these files get scrambled, startup crashes can result. That's why a Safe Boot moves all of these files into the Trash. (You'll even see them sitting there in the Trash after the startup process is complete, although there's not much you can do with them except walk around holding your nose and pointing.)

• Turned off your login items . Safe Mode also prevents any Finder windows from opening and prevents your own hand-picked startup items from opening ”that is, whatever you've asked Tiger to auto-open by adding them to the System Preferences Accounts Login Items list.

  This, too, is a troubleshooting tactic. If some login item crashes your Mac every time it opens, you can squelch it just long enough to remove it from your Login Items list.

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Tip: If you don't hold down the Shift key until you click the Log In button (after entering your name and password at the login screen), you squelch only your login items but not the fonts and extensions.

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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.

B.8.3. 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).

B.8.4. 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.

B.8.5. Forgotten Password

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.