Five Mac maintenance myths

You know you need to change the oil in your car every 3,000 miles, clean your house’s gutters every fall, and brush your teeth at least twice a day—but do you know what’s necessary to keep your Mac in good shape? For the most part, Macs run smoothly. But as with most machines, a little preventative maintenance goes a long way toward keeping things running smoothly.

This week, in our Essential Mac Maintenance series, I’ll show you what you need to do, starting today with how to Get Set Up. [Update: Check out how to Rev Up Your Routines.] But first, let’s talk about what you don’t need to do, despite what you may read in online forums or on email mailing lists. I call these things maintenance myths.

Myth #1: “You should repair permissions regularly.”

OS X’s permissions determine the access each user has to each item on a hard drive. If certain files have the wrong permissions, you can experience problems. So you’ll commonly hear that you need to use Disk Utility’s Repair Disk Permissions feature on your startup drive as a routine maintenance procedure.

But contrary to popular belief, repairing permissions—a procedure which simply resets permissions to a known state—works only on a particular subset of OS X system files. It doesn’t affect user files, nor does it affect third-party files or programs. In other words, it’s unlikely that regularly repairing permissions will prevent problems.

If you ever do have a problem with system-level permissions, your Mac will likely behave oddly, and you’ll usually be able to use the Repair Disk Permissions function then to fix the problem without any data loss or long-term effects. So I recommend repairing permissions as a troubleshooting tool rather than a maintenance task. For a comprehensive look at this topic, see Repairing Permissions: What you need to know.

Myth #2: “You need to run the Unix maintenance scripts.”

You may have heard about a collection of magical Unix maintenance scripts that OS X is supposed to run automatically. The story goes that because these scripts are scheduled to run in the middle of the night, putting your Mac to sleep or shutting it down prevents them from running—so you need to do so manually.

It’s true that there are Unix scripts that perform certain cleanup tasks in the early morning—one script every day, a second script once a week, and a third once a month. It’s also true that if you shut down your Mac every night, the scripts don’t run. However, the situation isn’t as dire as you might think. First, if you put your Mac to sleep at night, instead of shutting it down, Leopard is smart enough to run the missed scripts the next time you wake up your computer. (Tiger is supposed to do so, as well, although this automatic feature didn’t work as well.) Second, the tasks these scripts perform aren’t so important that a few missed executions will adversely affect your Mac.

The main script tasks involve cleaning out old log and temporary files and rebuilding Unix’s locate and whatis databases. If you’re a Unix geek, leave your Mac on (or asleep) on Friday nights so the weekly script can run at its normal Saturday-morning time. If you’re not a heavy users of locate or whatis, you’ll likely be fine running the scripts every few months just to clean up your log files. An easy way to run the scripts manually is by using Mike Vande Ven Jr.’s free Maintidget 1.3, a Dashboard widget that shows you the last time each script was run and lets you manually run one or all with a single click. There are also innumerable tweaking utilities that provide similar functionality

Myth #3: “You should periodically defragment your hard drive.”

If you save a file to your hard drive when there isn’t a large-enough block of contiguous free space for it, the file is broken into several smaller pieces. This is called file fragmentation. Some amount of file fragmentation is normal, especially as your hard drive gets full. But too much file fragmentation hinders performance—the more fragmented your drive is, the harder it has to work to read each file.

Because of this, people have long recommended defragmenting drives—regularly using a utility to rearrange file fragments on your hard drive so that each file resides in a contiguous block of hard-drive space—as routine maintenance. But with OS X, this procedure isn’t necessary for everyone, for several reasons. First, the Mac’s file system, HFS Plus, is quite good at avoiding file fragmentation. Second, the performance of today’s hard drives is so good that many users won’t notice even moderate fragmentation. Finally, OS X (10.3 and later) automatically defragments some files.

File fragmentation is an issue primarily for people with almost-full hard drives and people who work with very large files or large amounts of data (for example, video and some image files). If your drive is almost full, a better option is to free up space or upgrade to a larger drive. People who truly need to defragment—or optimize, which is defragmentation that also attempts to position particular types of files for optimal performance—can use utilities such as Prosoft Engineering’s $99 Drive Genius 2 or Micromat’s upcoming $98 TechTool Pro 5. (You may also hear about directory fragmentation. This is different from file fragmentation, and is addressed by utilities such as DiskWarrior.)

Note that you should always perform a complete backup of your drive before defragmenting it. In fact, an easy and relatively-safe way to defragment the files on your drive is to perform a clone backup using SuperDuper or Carbon Copy Cloner, erase the drive, and then restore the drive by cloning it from the backup.

Myth #4: “You should consistently clean your caches.”

To improve performance, OS X and some programs store frequently accessed data in cache files. (You’ll find these files in Caches folders located inside OS X’s various Library folders; there are also some caches files located in subfolders of /var/folders.) When the OS or a program needs this data, it can simply access the cache files instead of having to search for the original sources.

Many people recommend deleting cache files as regular maintenance, arguing that these files sometimes become corrupt. However, deleting cache files can have unwelcome consequences. Cache files exist because they improve performance; deleting them regularly means they won’t be available when normally accessed, and your Mac will have to recreate them from scratch. In addition, many of the most-frequently-accessed caches are regenerated automatically at startup or login, so there’s no need to manually delete them.

There are also more-specific drawbacks to deleting cache files. For example, deleting Leopard’s font cache files resets the disabled/enabled status of every font in Font Book. That’s not something heavy font users will appreciate if they’re not experiencing font-related problems. And the Metadata folder in ~/Library/Caches contains Spotlight information about some of your personal files, so deleting it means Spotlight will have to re-index that data.

As with repairing permissions, deleting cache files is better done as a troubleshooting step than as part of regular maintenance. If a cache file ever goes bad, it will likely cause problems with the program or function it’s associated with. For example, if your Web browser seems slow or crashes each time you launch it, there could be a problem with your browser’s cache files. Quitting the browser, deleting the cache files for that browser, and then re-launching the program may fix the problem. (Many browsers also have a built-in Empty Cache command.) If you’re having problems with fonts or garbled text, a corrupt font cache may be to blame. Mark Douma’s $10 Font Finagler 1.0 can verify and, if necessary, remove your font caches. If you suspect problems with system-level cache files, Northern Softworks’ $9 Leopard Cache Cleaner 4 can delete even caches you normally can’t access.

Myth #5: “You need to occasionally update prebinding”

In early versions of Mac OS X, you could speed up the launching of programs by updating the prebinding information stored by the OS; the procedure became a commonly recommended maintenance task. However, it hasn’t been necessary in years, and, in fact, offers no benefits under recent versions of Mac OS X. For more on the topic, see this description of the procedure.

[Senior Editor Dan Frakes has been writing about Mac maintenance and troubleshooting since the early days of the Power Macintosh.]