Solving Mac Disk and Hardware Problems

Part 2 - Disk & Hardware Problems

• Directory Damage or Your Mac Won't Boot
• Repairing File Permissions
• Nonvolatile Memory (PRAM)
• Other Mac Tricks

Directory Damage or Your Mac Won't Boot

The disk directory is the table of contents for your hard drive. Directory errors build up slowly over time - or quickly after a crash. Such errors can cause problems opening or saving files, and if severe enough they can prevent your Mac from starting up, instead displaying the flashing question mark. Fixing the disk directory and boot blocks often helps resolve these kinds of problems.

Create a Fresh New Directory

DiskWarrior is my tool of choice to fix directory related problems. You will need to restart your Macintosh from the DiskWarrior CD to fix the internal hard drive. When DiskWarrior is ready, select your startup drive and click Rebuild Directory. Replace your existing directory when the process is complete, then restart normally to see if your problem is fixed.

Repair the Damaged Directory

Other disk utilities are worth trying when DiskWarrior doesn't help. Apple's Disk Utility has a Repair Disk function that sometimes gets you going - you can restart from your Mac OS X Install CD/DVD and run Disk Utility to fix your startup drive. At a more sophisticated level, TechTool Pro and Drive Genius let you test for various hardware damage and try to repair errors; both also come on a bootable CDs or DVDs.

Rebuild the Desktop (Classic Mac OS)

For Mac OS 9 and Classic users, Apple's Rebuild Desktop routine can help fix problems opening files in Mac OS 9 applications. For Classic Users running Mac OS X, use System Preferences --> Classic --> Advanced tab to rebuild the desktop. If you're booted in Mac OS 9, restart the Mac while holding down the Command (Apple) and Option keys (Cmd-Opt) simultaneously until you are asked if you want to Rebuild the Desktop.

Repairing File Permissions

File Permissions are security settings that permit or restrict access to files and folders by different users. This security helps prevent you from modifying special system files you shouldn't change and prevents other users from seeing the files inside your Home folder when you share a machine. The easiest way to view or set a file's permissions is to select the file (or folder) and choose Get Info in the Finder (File --> Get Info, or Cmd-I). The Ownership & Permissions area shows who can do what with that file.

While noble in intent, incorrectly set file permissions can sometimes prevent you from launching applications or saving files. They can also cause problems with OS updates. Apple is aware of this and provides a way to Repair Permissions that restores defaults and fixes many problems. Use Apple's Disk Utility, select your boot drive, then choose the First Aid tab (if necessary) and click Repair Permissions. Let the process run completely.

Tip: Repair Permissions before and after any System Software updates for best results.

Nonvolatile Memory (PRAM)

The contents of your computer's RAM are normally lost when you shut down, but some settings are saved when the power is off: the date and time, your network settings, choice of startup disk, etc. These settings are stored in a special type of RAM called Nonvolatile RAM (NV-RAM) or Parameter RAM (PRAM). A small battery on the motherboard powers this special RAM when the computer is turned off.

Zap the PRAM

Sometimes the PRAM gets corrupted, especially after a hard crash. Corrupt PRAM can prevent your Mac from booting and causes all sorts of strange errors. Resetting (or Zapping) the PRAM can fix problems like these: restart your Mac, and after it chimes hold down the Command (Apple), Option, P, and R (Cmd-Opt-P-R) keys simultaneously. After a few seconds the system will restart again and chime a second time. Now release keys the keys and boot normally.

Replace the Battery

Another problem could be that the PRAM backup battery may be dead. This is typically a 3.6V Li-ion battery which lasts about five years. If the date and time on your computer are wrong each time you unplug your Mac, it's time to replace the battery. The battery is accessible on most tower Macs, otherwise a Mac service center can do this for you.

Other Mac Tricks

Eject a Stuck CD or DVD

To eject a stuck CD or DVD, especially with a slot loading drive, try this: restart your Mac and hold down the mouse or trackpad button continuously until the disc ejects. The works 90% of the time.

Open Firmware

On PowerPC-based Macs you can also Boot into Open Firmware (which really impresses your friends and coworkers). Open Firmware is Mac's BIOS and provides a few additional options for sick systems. Restart your Mac, and after the chime hold down the Command (Apple), Option, O, and F (Cmd-Opt-O-F) keys simultaneously. Eventually the system will boot to a white screen with ok> prompt.

You can very thoroughly zap PRAM from this screen, even better than using Cmd-Opt-P-R. Type the following lines:

ok> reset-nvram <RETURN>
ok> reset-all <RETURN>

The system will then reboot.

You can also use Open Firmware to eject CDs/DVDs that won't eject any other way:

ok> eject cd <RETURN>

Sadly, the Intel-based Macs do not have Open Firmware, so equivalent tricks are still waiting to be found. 

Next: Maintaining Your Mac, Part 3: Effective Backup Strategies for Mac Users

This article was originally published on Adam's Oakbog website. It has been adapted and reprinted here with his permission.