Lombard PowerBook G3 Won't Boot Off 8.6 CD

[Tim Seufert]

On Dec 15, 2003, at 10:10 AM, Chris Horn wrote:

> My only guess as to why it won't boot into Mac OS off the CD now is 
> that
> the Mac OS boot CD needs to set up some swap space (Virtual Memory) or
> something on the disk, but the partitioning is wrong for it.

A MacOS 8.6 CD shouldn't need a hard drive at all to boot.  For that 
matter I'm fairly sure even OS X boot CDs don't try to set up swap, at 
least not until after installation has begun.  (One of the functions of 
an OS X boot CD is to repair damaged partitions, so it can't mount any 
HD partitions read/write until the user decides to install to one of 
them.)

> FWIW - I also can't boot off the YDL CDs that I used to install YDL 
> just a
> couple of weeks ago.  This leads me to believe that something more 
> serious
> is wrong with the machine than just not booting off it's OS 8.6 CD.

Forgive me if you've mentioned trying it already, but you might want to 
try removing and reseating the CD-ROM or DVD-ROM drive in your Lombard. 
  If you're still able to boot Linux you should also see if it can mount 
the YDL CDs.

> Does putting Linux on the machine fundamentally change any of the boot
> process?  I know that Yaboot has replaced whatever on the MBR, so 
> could my
> problem be related?

No, Linux doesn't fundamentally change the boot process.  I'll try and 
give you a capsule summary of what's going on because that may help you 
to diagnose your problem.

There actually isn't even a MBR to replace, because Open Firmware is 
smart enough in New World Macs that it knows how to read any arbitrary 
file from a HFS or HFS+ filesystem.  Thus, the yaboot bootloader is a 
file installed on a small HFS partition created for the purpose of 
bootstrapping Linux.  The only difference between that partition and 
any other HFS partition is that the partition's type in the partition 
table is set to "Apple_Bootstrap" instead of "Apple_HFS", which 
prevents MacOS or MacOS X from automatically mounting it but doesn't 
keep OF from seeing it.

After installing yaboot onto its little partition and "blessing" it 
(setting up some special directory and file attributes to make OF 
recognize the yaboot file as a valid file to boot from), Linux simply 
points the Open Firmware "boot-device" variable (which is stored in 
nonvolatile RAM, not on disk) at that partition.  This is the same 
stuff MacOS does to get OF to boot a bootable MacOS partition.

If the boot-device variable is blank or points to a partition which 
isn't set up correctly, OF will search all available disks (including 
CDs) for HFS/HFS+ partitions with bootable files, and will boot the 
first one it comes to.

If you hold down C immediately after powering up or rebooting, OF will 
try to boot a CD first regardless of the boot-device setting.  About 
the only way Linux (or any other OS) could keep CD booting from working 
is to screw up OF variables other than boot-device badly enough to 
prevent OF from using the CD.  Linux typically never alters anything 
other than boot-device so this is unlikely.  (Also, if that was your 
problem I'd have expected the firmware reset tricks to fix it.)

Speaking of firmware resets, one thing that hasn't been mentioned so 
far is the reset button.  It's on the back of the computer between the 
VGA and modem ports.  It may or may not help...