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.
Author: David Pogue / ISBN: 0-596-00941-0

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.

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.

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).

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?

• Checked your harddrive.
  The Shift-key business makes the startup process seem to take a very long time; behind that implacable Apple logo, Tiger is scanning your entire hard drive for problems. it's running the same disk check that's described on page 779.
  
  
• 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.

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.

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.

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.

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:

• Your Mac freezes during startup, either before or after the Login screen.
  
  
• The startup process interrupts itself with the appearance of the text-only command line.
  
  
• You get the "applications showing up as folders" problem.

Method 1: Disk Utility

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:

1. 1. Start up the Mac from the Tiger DVD or CD.

   The best way to do that is to insert the disc and then restart the Mac while holding down the C key.

   You wind up, after some time, at the Mac OS X Installer screen. Don't be fooled—installing Mac OS X is not what you want to do here. Don't click Continue!

2. 2. Choose Utilities→Disk Utility.

   That's the unexpected step. After a moment, the Disk Utility screen appears.

   TIP: You could also skip steps 1 and 2 by starting up from an external hard drive, like an iPod onto which you've installed Mac OS X. Just run its own copy of Disk Utility to check your Mac's hard drive.

3. 3. Click the disk or disk partition you want to fix, click the First Aid tab, and then click Repair Disk.

   The Mac whirls into action, checking a list of very technical disk-formatting parameters.

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.

NOTE Don't be alarmed. The message's last line says "Repair completed" whether or not any repairing was done at all.

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 # prompt—see 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.

TIP: You've probably gone to this trouble for the sake of running fsck, the Unix diskchecking program. But you can also use ls, cd, rm, or any of the other Unix commands described in Chapters 16 and 17.

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:

• The volume Macintosh HD appears to be OK. All is well. Type exit and press Return to proceed to the usual Login screen and desktop.
  
  
• File system was modified. A good sign, but just a beginning. You need to run the program again. One fsck pass often repairs only one layer of problems, leaving another to be patched in the next pass. Type fsck -y a second time, a third time, and so on, until you finally arrive at a "disk appears to be OK" message.
  
  
• Type exit at the prompt and press Return to get back to the familiar world of icons and windows.

Where to Get Troubleshooting Help

If the basic steps described in this chapter haven't helped, the universe is crawling with additional help sources.

Help Online

These Web sites contain nothing but troubleshooting discussions, tools, and help:

• MacFixIt (www.macfixit.com). The world's one-stop resource for Mac troubleshooting advice.
  
  
• Mac newsgroups (such as comp.sys.mac). A newsgroup is an Internet bulletin board, which you can access using a program like Microsoft Entourage or Unison (www.panic.com). If you're polite and concise, you can post questions to the multitudes here and get more replies to them than you'll know what to do with.
• Apple's help site (www.apple.com/support). Apple's help Web site includes downloadable manuals, software updates, frequently asked questions, and many other resources.
  
  
• It also has a Search box, which may look mild-mannered but is actually the mother of all troubleshooting resources: the Knowledge Base. This is the collection of 50,000 individual technical articles, organized in a searchable database, that the Apple technicians themselves consult when you call for help. You can search it either by typing in keywords or by using pop-up menus of question categories.

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.

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