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.
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. That’s a lot better than the Mac OS X 10.0 and 10.1 effect: random text gibberish superimposing itself on your screen.
(In such situations, user panic might be the more applicable term, but that’s programmers for you.)
If you experience a kernel panic, it’s almost always the result of a hardware glitch—most often a bad memory (RAM) board, but possibly an accelerator card, graphics card, or USB hub that 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 OS X’s bad hair day. If you’re able to pinpoint the culprit, seek its manufacturer (or its website) on a quest for updated drivers, or at least try to find out for sure whether the add-on is compatible with 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 updates from the Support area of Apple’s website (if indeed OS X’s own Software Update mechanism doesn’t alert you to their existence).
There’s one other cause for kernel panics, by the way, and that’s moving, renaming, or changing the access permissions for OS X’s essential system files and folders—the Applications or System folder, for example. (See The Get Info Method for more on permissions.) This cause isn’t even worth mentioning, of course, because nobody would be that foolish.
In times of troubleshooting, Windows fans press an F-key to start up in Safe Mode. That’s how you 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, 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; as the progress bar suggests, OS X is actually scanning your entire hard drive for problems.
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 noncritical kernel extensions (drivers). All kinds of software nuggets load during the startup process. Some of them you choose yourself, like icons you add to the Login Items list in the System Preferences→Accounts pane. Others are normally hidden, including a large mass of kernel extensions, which are chunks of software that add various features to the basic operating system. (Kernel extensions live in your System→Library→Extensions folder.)
If you’re experiencing startup crashes, some non-Apple installer may have given you a kernel extension that doesn’t care for OS X 10.11—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 OS X actually needs to run, which are in your System→Library→Fonts folder).
Trashed your font cache. The font cache is a speed trick. OS X stores the visual information for each of your fonts on the hard drive so the system won’t have to read every single typeface off your hard drive when you open your Font menus or the Fonts panel.
When these files get scrambled, startup crashes can result. That’s why a Safe Boot moves all 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 handpicked startup items from opening—that is, whatever you’ve asked your Mac 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 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, or use certain microphones and speakers. (The next time you restart, all 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.
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).
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.
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 The Forgotten-Password Survival Guide.