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OSXFAQ Mac OS X Tip-of-the-Day 
Trouble-Shooting IV (Advanced) - Kernel Panics
By Adrian Mayo - Editor - OSXFAQ
About the Kernel and Extensions
Mac OS X's kernel is based on the Mach kernel and is called XNU. The
kernel is responsible for Mac OS X's pre-emptive multitasking, virtual
memory, protected memory, basic I/O, and such like. It controls all
other running processes, confining them to their own 'cell' so they
cannot interfere with each other or with the kernel itself. This
confinement is what gives Mac OS X a lot of its stability - an errant
process cannot make waves throughout the whole system.
Normal processes run with the processor (PowerPC) in an unprivileged
mode: this is the mechanism by which they are confined to their
individual cells. They are not allowed direct access to the machine
hardware.
The kernel runs in privileged mode and has full access to the hardware
- memory, disc drives, peripherals, etc. If the kernel crashes then
everything goes down. A stable kernel gives Mac OS X stability.
Most instability is caused by device drivers. Device drivers need
access to the hardware, and so need to run in privileged mode. They
are therefore implemented as extensions to the kernel, also known as
kernel extensions or .kext files, and run in 'kernel space'.
Kernel extensions can be divided into those supplied by Apple as part
of Mac OS X, and third party extensions usually installed when
additional hardware is added. Both types can be found in the folder
System:Library:Extensions. Most instability lies in third party
extensions.
When the kernel, or a device driver crashes, you experience what is
called a Kernel Panic. This can be recognised by:
- a white box of text in many language set on a dimmed screen
- complete unresponsiveness of the machine
A Kernel Panic may happen very occasionally, say one or twice a year.
If it happens regularly, suspect any newly-installed device drivers.
Trouble-Shooting Steps
Boot with only Apple-supplied extensions. Restart you Mac with the
space bar held down to perform a 'safe boot'. This skips non-Apple
startup items too.
If safe boot works, uninstall recently-installed third party drivers.
If there are no uninstall instructions, then locate the suspect
extension (/System/Library/Extensions), temporarily remove it, and
reboot.
Use the Terminal to delete the files /mach and /mach.sym. You will
need root permissions to do this. Normally these are deleted and
re-built automatically each time the machine is booted.
If the machine is very slow at booting or running, remove the extension
cache files:
/System/Library/Extensions.kextcache
/System/Library/Extensions.mkext
These will be re-built when the machine is rebooted.
Enjoy !! :-)
Panther 10.3.8
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