Through no fault of your own, your Mac may one day decide not to work, displaying anything from odd behaviour to a truculent refusal to do pretty much anything. Don't be tempted to reach straight for the phone and book it in for a spot of expensive repair; try these two simple steps first. They solve most problems with Mac OS X.
First, a reminder: always maintain a backup of your data. Better still, backup your data in multiple ways to multiple locations. For example, you may wish to use Backup as supplied to subscribers to Apple's .Mac service to save your address and calendar data to your iDisk automatically at 5 o'clock and your iPhoto library to DVD every two weeks, and then make a full backup of your system to an external hard disk using Mike Bombich's excellent Carbon Copy Cloner tool once a month.
STEP 1 CHECK THE DISK STRUCTURE
Many problems your Mac may have arise from it not knowing where files are on your hard disk. This would be no more than irritating if it was just your own documents that went missing, but if your Mac can't find vital system files, problems can creep in.
Restart your Mac and hold down the Apple and S keys as soon as you hear the startup chime. Continue to hold down both keys until you see a black screen with white text, like this one:
Don't panic! For seasoned Mac users, this looks terrifying, but you won't be here for long. (And don't worry if your screen doesn't look identical to the one above; the text displayed will differ from system to system.)
Wait until the text stops scrolling and you get the localhost:/ root# prompt as shown above. Carefully enter the relevant command for your operating system, noting spaces, then press Return:
Mac OS X 10.0 – Mac OS X 10.2.8
/sbin/fsck -y
Mac OS X 10.3 and later
/sbin/fsck -fy
Your Mac will then begin to check where files are on the disk and making repairs to the directory where necessary. If all goes well, you'll get a message like the one below:
If you don't get a line telling you that your disk appears to be OK – even if it tells you that repairs were completed successfully – you need to run the tests again, and keep cycling until your Mac reports that the disk is fine. With Mac OS X 10.4, it will do this automatically, but with earlier versions of Mac OS X, you'll have to tell your Mac manually to run the check again. The easiest way to do this is to press the up arrow on your keyboard which will simply repeat the last command entered, then press Return again.
Once your hard disk 'appears to be OK' type the following command, then press Return:
shutdown -r now
Your Mac will then restart back into the familiar Mac operating system, from where you can carry out step two.
Note that you can accomplish the same thing booting from your system CD or DVD and using Disk Utility to Verify Disk; Apple encourages users of Mac OS X 10.4 to use Disk Utility for directory structure repair where possible.
For more information on this technique, read Apple's technical document on the subject.
STEP 2 REPAIR PERMISSIONS (Mac OS X 10.2 and later)
Your Mac uses a system of permissions to track who can do what to the files it holds. This may sound innocuous – and usually is, especially if we're just talking about your own documents – but the permissions of some files important to the running of your Mac can become corrupted. If this happens, and your Mac can't access files it needs in order to accomplish certain tasks, it will start behaving erratically. Repairing these permissions is easy though. Launch Disk Utility (it's in the Utilities folder in your Application folder) then click on your hard disk. Assuming it has Mac OS X installed on it, you'll be able to click on the Repair Disk Permissions button.
Your Mac will then go through the files on the hard disk, checking to see that permissions are set correctly on each, and making amendments if necessary. In doing this, it checks off your files against receipts stored in your top-level Library folder. It's good practice to repair permissions after installing software, especially after performing any system upgrade using Software Update or installer CDs.
For more information about permissions, read Apple's technical document on the subject.
HAPPY MAC AGAIN
Together, these two simple steps should solve many of the problems you're likely to encounter in day-to-day use of your Mac. If it's still playing up after you've done both, you'll need more professional help, but you're likely to be pleasantly surprised.
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