B.6. 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 egofsckis 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.
B.6.1. 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 fix the disk it'son(except for permissions repairs, described at the
beginning of this appendix).That's why you have to restart the computer from the
Leopard installation disc (or another startup disk), and run Disk Utility from there. The
process goes like this:
1. Start up the Mac from the Leopard DVD.
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 isnotwhat you want to do here. Don't click Continue!
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 yourMac'shard drive.
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 begoodnews. 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).
B.6.2. Method 2: fsck at the Console
Disk Utility isn't of much use when you can't find the Leopard DVD, when your DVD
driveisn'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 programfsck, for which Disk Utility
is little more than a pretty faceplate.
Like any Unix program,fsckruns at the command line. You launch it from the all-text,
black Unix screen by typingfsckand pressing Enter. (As discussed in the box on the
facing page, you can also usefsck -f.)
You can't, however, just runfsckin 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.
B.6.2.1. 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.
POWER USERS' CLINIC
Journaling vs. fsck
Mac OS X 10.5 comes withjournalingturned on. As noted on Section A.6
journaling means that the Mac keeps a diary about every tiny bit of hard drive
activity. In event of a crash or freeze, the Mac knows precisely what was going
on at the time, and precisely which files might have been damaged.
In theory, then, you'll never need fsck at all. After all, there's nothing to check.
The Mac's journaling software is always on top of things—and, if the journal
indicates that there was trouble saving a file, Mac OS X can finish or undo the
change.
Even Apple concedes, however, that in the real world, things can still go wrong,
even with journaling turned on.
That's why, when you attempt to usefsckas described on these pages, a message
will inform you that, hey, you don'tneedto repair your disk. Thanks to
journaling, there's no damage to repair.
If you decide to proceed on the off chance that something's gone wrong behind
your journal's back, just use the-fflag to force the disk check, like this: fsck -f.
Note, however, that you may see a series of phony error messages when you do
this. If you see any of these messages, you should ignore them:
• "Volume bitmap needs minor repair"
• "Invalid volume free block count" or "block count changed from XX to
YY"
• "Volume header needs minor repair"
• "Incorrect block count for file"
If you see anyothererror messages, though, let fsck go ahead and repair them.
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.
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.
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.3.)
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.
FREQUENTLY ASKED QUESTION
Viruses? What Viruses?
One great thing about the old Mac OS was that there were hardly any viruses to
worry about—all of the nasties seemed to be written for Windows. But now that
we're using Unix, which has been around for 30 years and has a huge user base,
is it time to worry again?
Nope. There are even fewer viruses for Unix than for the Mac OS.
You still need to be careful with Word and Excel macro viruses, of course. If
you open a Word or Excel attachment sent by email from someone else, and a
big fat dialog box warns you that it contains macros, simply click Disable
Macros and get on with your life. And you still need an antivirus program for
Windows if you run it on your Mac (Chapter 8).
Otherwise, you have little to worry about. After six years, there hasn't been one
single Mac OS X virus outbreak—partly because virus writers have a smaller
"audience" in Mac fans, and partly because Mac OS X is more difficult to hack.
Sleep well.
At the localhost # prompt, type fsck -y (note the space before the hyphen) and press
Enter. (The y means "yes," as in "yes, I want you to fix any problems automatically.") If
the Mac refuses because journaling is turned on (Section A.6), you can also typefsck -fy
to force the disk check.
Tip: You've probably gone to this trouble for the sake of running fsck, the Unix disk-
checking program. But you can also use ls, cd, rm, or any of the other Unix commands
described in Chapter 16.
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. Onefsck pass often repairs only one layer of problems, leaving
another to be patched in the next pass. Type fsck -ya second time, a third time, and
so on, until you finally arrive at a "disk appears to be OK" message.
Typeexit at the prompt and press Return to get back to the familiar world of icons
and windows.
TROUBLESHOOTING MOMENT
The Reinstall
When some component is missing, your troubleshooting steps have failed, and
Mac OS X continues to act up, consider reinstalling Mac OS X.
That's not a big deal at all. It involves inserting the Leopard DVD, restarting the
Mac, pressing the C key as the computer starts up, and proceeding with the