Prevent Mac Disasters

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Even Perfect Disks Have Imperfect Permissions

The Repair Disk Permissions function works by comparing each folder’s actual permissions with a master list of the expected permissions for that folder. If there’s a difference between the actual and the expected, Repair Disk Permissions modifies the folder to match the master list.

But there’s a glitch in the process—if you run Repair Disk Permissions and then immediately run it again, you should get a clean bill of health, since everything was just repaired. But you won’t. Instead, you’ll probably see this in the output section: “We are using special permissions for the file or directory ./System/Library/ Filesystems/cd9660.fs/cd9660.util. New permissions are 33261.”

You can safely ignore this message.

To Defrag or Not to Defrag

Although some maintenance procedures are no-brainers, others are debatable. Take defragmenting your hard drive. Mac OS saves files in small pieces across your hard drive, rather than in contiguous chunks of free space. The fuller your hard drive is, and the more you’ve saved and deleted files over time, the worse file fragmentation can be. It can slow down hard-drive access times, since your hard drive has to work harder to find all the pieces of each file. And the disk directory for a fragmented volume is much more complex than one for a relatively fragment-free drive, which can increase the chances of directory problems.

Defragmenting joins fragmented files and moves them to contiguous blocks of free space on a drive. Although it sounds like a good idea, there’s disagreement about whether it’s necessary in OS X. With OS X 10.3 and later, if you have disk journaling enabled (it’s enabled by default), OS X performs a limited degree of defragmentation of smaller files during the normal course of operation. Many users shouldn’t give fragmentation a second thought.

But if you work with extremely large files—for example, huge Photoshop images or digital video files—you may find that a defragmented drive performs better. Although there are a few utilities for defragmenting volumes in OS X, my favorite is TechTool Pro 4. (Warning: Before defragmenting any volume, verify the integrity of the drive and back up any important files. The process involves copying and deleting most of the files on the drive, so any problems can result in data loss.)—DAN FRAKES

Run, Scripts, Run!

OS X uses Unix maintenance scripts to keep your hard drive tidy. These are run by the Unix scheduling utility cron, but only if your Mac is awake in the wee hours of the morning. If it isn’t, you’ll need another way to execute these actions.

If you’re someone who remembers to rotate your mattress regularly, you’ll do fine with the free MacJanitor, from Brian Hill, which lets you manually run each script—or all three—at the click of a button whenever you like. If you’d rather not have to remember such mundane tasks, Macaroni, from Atomic Bird, will check, each time you start or wake up your Mac, to see whether the scripts were run on schedule; it will automatically run any tardy script for you.

But if you’re a geeky user who wants to decide exactly when these scripts run and to understand exactly what’s going on behind the scenes, check out “Easy Mac Maintenance”. This step-by-step article shows you how to use the free utility CronniX to edit your Mac’s system crontab and reschedule the maintenance scripts.—DAN FRAKES

Tip: Find Corrupt Preference Files Fast

To simplify using the plutil utility in Terminal, select File: Save As, give the file a name (such as Check My Permissions), and pick a location. In the When Opening This File section, select Execute Command In A Shell, click on the Execute This Command (Specify Complete Path) button, and enter either of the commands in this section. Click on Save, and you’ve got a clickable file. In the future, simply double-click, enter your password when prompted, and press return.

Tip: Detect Available Hard-Drive Space

Although software warns you of impending hardware failures, it won’t help you with the primary cause of poor hard-drive performance: full disks. Keep at least 10 percent of your boot drive free. To see how much space you have available, highlight the boot drive in the Finder and press Command-I (Get Info).

Tip: Routine Maintenance Reminder

Set up a repeating event in iCal or Outlook and call it Mac Maintenance. When the reminder pops up, take a routine-maintenance break.

When you run Disk Utilities’ Repair Disk Permissions feature, you’ll see messages explaining which files and folders had incorrectly set values.
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