The plot thickens. Reference, of course, my previous posts on this subject here.
I had narrowed the culprit down specifically to /System/Library/Caches/, which seems to somehow become corrupt after some major system maintenance or modification (i.e., install of a new kernel extension or cache clean up) on my old G4 AGP (Sawtooth).
Some others on the Apple forums had suggested it could possibly be due to my Acard 6280M IDE PCI adapter, which I MAY have ruled out by updating to the latest driver (version 1.5.7.); I’m not 100% sure. I did have some troubles updating to the new Acard driver, but I eventually got it working as well as the previous version of the Acard driver I was using.
However, after reinstalling (once again) Tiger 10.4.5 from the backup I had made and migrating (again, avoiding the root files and folders--which I no longer believe is related to the problem), I installed Applejack and proceeded to clean all the caches in single-user mode to test for problem reproducibility. The system rebooted fine after the Applejack session, but I immediately rebooted again from the Finder and experienced the hang at the gray Apple screen.
Since I had narrowed the problem to /System/Library/Caches/, I decided to go through the contents systematically to find the culprit file or folder. As Murphy’s Law would have it, the very last folder I deleted (after many reboots, gray screens, and safe boots to delete files) was this folder:
After deleting this folder, the system booted normally, so I may need to delete this folder after every kernel extension install or system maintenance that involves cache cleaning.
What fun! This obviously MUST be related to my hardware setup in some way, but I don’t know which part for the life of me (maybe it is the Acard, but I can’t understand why). I do have these system.log messages (the first of which I always had in Panther but never had any real issues booting):
Mar 5 09:51:04 localhost kernel: WARNING: ATA Drive claims FLUSH CACHE EXT feature support but does not claim Extended LBA feature support
The above message obviously directly involved the Acard adapter.
Mar 5 09:51:04 localhost kernel: Extension "com.apple.driver.PioneerSuperDrive" has no kernel dependency
The next message listed above is a new one for me. No clue...
So there’s obviously some issue with hardware, because my Mac Mini doesn’t behave this way on Tiger (and obviously for most of the Apple world). My old AGP has been so heavily upgraded that it may no longer be capable of running newer OSs (likely issues with either the Acard or my Giga Designs Dual Processor upgrade card).
Anyway, at least I’ve narrowed it down some to a kernel issue with some part of the hardware.