Crash Survival

Sooner or later your Mac will crash. Software often fails, sometimes for inexplicable reasons, or simply because an application or system file conflicts with another piece of software. Hopefully, after a crash, your computer will start up as usual, although you may have to reinstall the application or replace the document that was open at the time of the crash.

You can often fix disk damage by restarting your computer from the Mac OS X Installer CD, running the Disk Utility application, selecting First Aid and clicking on Repair Disk. If the problem remains, you should zap the PRAM by restarting the machine and holding down -Shift-P-R until you hear three chimes. If this doesn’t work, disconnect any external hardware or special expansion cards and try starting up once more. Failing this, you’ll have to use Disk Utility to format the drive and then reinstall your software and data. Of course, this assumes that you’ve got a full backup of the drive.

You did do a backup, didn’t you?

The Startup Process

When a Mac is turned on the startup initialisation process begins. The power-on self-test (POST) procedure checks the machine’s hardware, including its RAM. If successful, the Mac produces the familiar C major chord, the ‘Quadra sound’ or some other friendly noise. The Startup Manager in the Mac’s ROM then searches for a startup disk. If there’s a valid system, the Boot Blocks are read from the startup disk and the system is loaded into memory.

A POST failure, which usually results in an unpleasant sequence of sounds or notes, is caused by problems with the system, a virus or a hardware fault. First, switch the machine off and disconnect all peripheral devices, including external disk drives, and try again. If that fails, remove any additional hardware, such as expansion cards, and start once more. Following this, try starting from the Mac OS X Installer CD. Sadly, if this doesn’t work you may have to visit an engineer.

In some instances the POST is successful but a valid system or data isn’t found on any drive, in which case you may have to reinstall the system. However, this kind of problem can also be caused by damage to the formatting of your startup drive, which can sometimes be repaired by starting from the Mac OS X Installer CD and using the Disk Utility application.

To summarise: if crashes keep happening at startup you should try each of the following in turn:-

  1. Use Disk Utility, as described above
  2. Check for viruses
  3. Disconnect external devices
  4. Remove extra expansion cards
  5. Reinstall the system
  6. Zap the PRAM

Hardware Control

During startup you can press various key combinations to change the machine’s behaviour, such as:-

Key(s)Effect
ShiftSafe mode (kernel extensions and login items disabled)
OptionShows Startup Manager (for selecting alternative startup disk)
-Shift-Option-DeleteStarts up from alternative drive
-Shift-P-RZaps Parameter RAM (PRAM) *
-Option-O-FCommand line •
-SSingle-user mode
-XForces startup in OS X if machine also supports OS 9.x
CStarts up from CD-ROM
TFireWire Target Disk mode (machine acts as drive for another Mac)

* Keys must be held until second startup sound occurs

Type eject cdat to force out a CD

Whilst in use, your computer can be controlled using the following keys:-

Key(s)Effect
Ctrl-EjectShows Restart/Shut Down dialogue
(pressed quickly)Shows Restart/Shut Down dialogue
(held for 5 seconds)Emergency Shut Down *
-Interrupt (for debugging) †
-Ctrl-Reset (Emergency Restart) *
Shift-fn-Ctrl-Reset (Emergency Restart) on some PowerBooks *
-Shift-Option-Reset (Emergency Restart) on iMacs *
-Option-EscapeForces application to quit •

* Changes in unsaved documents are lost and system damage may occur

Special software required for continued use of computer, otherwise system can be damaged

Changes in unsaved documents are lost: other applications can be used

Some machines also have hardware Interrupt or Reset buttons that have a similar effect to some of these combinations. The Interrupt button, often at the rear of the computer and designated by a circular symbol, intercepts the operation of the processor. The Reset button is often adjacent to the Interrupt button and usually designated by a triangular symbol.

  Solving Problems

Many computer problems are caused by corrupted data or faulty formatting on the internal drive.

Diagnoses

Before assuming that you have disk problems you should look at other possibilities. For example, if your Mac starts normally but you have difficulties with particular documents or applications, then the problem may be related to corrupt files, in which case your drive is probably intact.

In this situation, the first line of attack is to find and remove the offending items. If your problem’s limited to one document you could try repairing it with special utilities, although you’re likely to end up trashing it. If the trouble is restricted to one application, whatever document you’re working on, the application itself may be damaged (in which case you should install it again) or it may be incompatible with your version of Mac OS X or some additional software.

Preferences Files

Problems with a particular application can be caused by a corrupted preferences file. These reside in the Preferences folder in your home folder and usually have a filename extension of .plist. If necessary, try quitting the application, dragging the relevent file out of the folder and running the application again. If it now works normally you should dispose of the file, although your preferences for that application will be lost. If nothing changes, you should put the file back.

Mac OS X Permissions

Mac OS X is based on Unix, which employs permissions to restrict the access to certain files to specific users. Unfortunately, things can go wrong, preventing your applications from using your own files, which can lead to various problems. You can check your machine’s permissions by running Disk Utility, going to First Aid and clicking on Verify Disk Permissions. If errors are reported you should click on Repair Disk Permissions to put things right.

  Repairing Disks

To repair your drive properly you must have a CD containing a valid version of Mac OS X as well as the appropriate disk utilities. Ideally you should use the Mac OS X Installer CD, although a third-party drive may require alternative software. Note that additional drives that require special software may fail to mount when you start up from the Installer CD.

Having acquired a suitable CD you should proceed as follows:-

  1. Start the machine from your chosen CD.
  2. Run Disk Utility, click on First Aid and on Repair Disk, doing this several times, if necessary.
  3. Reinstall Mac OS X, if you want to be on the safe side.
  4. Zap the PRAM.
  5. Check the PRAM batteries, if possible.

This is only a guide. For example, if you’ve just installed a new drive you should check this first. If you’ve recently added additional software you should check to see it it’s suitable for your machine and your version of Mac OS X. Note, however, that the removal of some software can be very difficult, often requiring you to install the system from scratch.

  Recovering Files

Having got the drive to work you’ll need to check that your files are intact. If all files are present and correct you’ve nothing to worry about. However, if some are missing, or you’ve had really serious problems, you should erase the disk and start again: but only do this if you’ve got a complete set of backup disks!

Sometimes the original data isn’t visible on a drive because the files are damaged or the disk’s directory is faulty. If you haven’t got any backup don’t erase the disk. Instead, you can use a recovery utility, such as DataRescue X (ProSoft) or VirtualLab Data Recovery (BinaryBiz) to reconstruct the files. These applications normally require you to transfer the recovered files to another drive, thereby avoiding the possibility of damaging any other data on the original disk.

  Crashes

Software fails when a request generates an unexpected result. This can occur when one application intrudes into the memory space allocated to another program: this is commonly known as an exception error or invalid page fault. Such an event is rare in Mac OS X, since the system dynamically controls the memory assigned to each application.

Sometimes a program tries to execute an unrecognised command, known as an illegal operation, or a bug in the program creates a silly computation (perhaps dividing a number by zero), or it gets stuck in a software loop. As a result, it can freeze, ignoring any actions and leaving you with a locked, missing or empty dialogue, an immovable or non-existent pointer or a locked menubar clock. However, you should be able to use at least one of following key combinations:-

KeysEffect
-.Stops current operation
-SSaves current open document
-Option-EscapeForces the application to quit

You shouldn’t need to restart your computer after forcing an application to quit. However, if the system itself collapses you may see a perpetually spinning beach ball, indicating a kernel panic, which means a restart is inevitable.

Minimising Crashes

If you suffer from regular crashes, whatever the application, you should:-

  1. Check that any third-party kernel extension files are suitable for your system
  2. Check for viruses
  3. Reinstall Mac OS X
  4. Zap the PRAM

Viruses

Viruses are portions of executable computer code, created by intelligent but misdirected individuals who get some kind of pleasure from upsetting other people’s computers. Generally speaking, viruses are conveyed via applications, although they are also found in documents that contain macros, such as Word files and in Web files that contain Java commands.

If you don’t have access to the Internet, use reputable software and rarely exchange files with others, you’re unlikely to experience a virus. Other users should take the following precautions:-

Shut Down and Restart

Wherever possible, you must shut down or restart your computer using one of the following methods:-

  1. Pressing and clicking the required button.
  2. Pressing Ctrl-Eject and clicking the required button.
  3. Logging out and clicking on Shut Down or Restart in the login window.
  4. Choosing Shut Down or Restart in the Apple menu and clicking on the required button.

On shut down the the computer clears its memory (RAM), apart from the 256 bytes of Parameter RAM (PRAM) that’s used by the system to memorise special information. A restart implements a software reset, directing the processor back to its starting point without clearing the main RAM, although any corrupt data is later overwritten in normal use.

Reference

Mac OS X Bible, Panther Edition, Sam A Litt, et al, Wiley Publishing Inc, 2004

©Ray White 2004.