[ydl-gen] Uninstall 4.01

[Eric Dunbar]

On 3/13/06, Kenneth Browne <kbrowne at alumni.umass.edu> wrote:
> Eric Dunbar wrote:
> > On 3/12/06, Kenneth Browne <kbrowne at alumni.umass.edu> wrote:
> >
> >> Hello,
> >>  I have a G4-400 with  OSX on one disk and  YDL 4.01 on the other. Most
> >> times when booting into either OS there seems to be an exceeding long
> >> delay while the machine tries to sort out the two hard disks. When I
> >> boot into OSX "searching local drives" takes forever although I
> >> eventually get booted and all is OK. The YDL disk does not show up on
> >> the OSX desktop, which makes me think the drive is on the verge of
> >> failure. I say "on the verge" because at times the boot process goes
> >> normally. Other times, when I try to boot YDL the system just hangs at
> >> the Yaboot prompt. (It should boot through to Linux with no intervention
> >> if everything is working.)
> >>
> >> Here's my question: If I just want to ditch YDL can I simply set the OSX
> >> disk as my boot disk and remove the offending YDL hard disk, or is there
> >> a Master Boot Record (Ya-bootloader) somewhere on the Mac disk that
> >> needs to be removed?
> >>
> >
> > AFAIK you don't even need to bother setting the OS X disk as your
> > startup disk (to use Mac parlance) as your Mac should search all
> > attached drives for a bootable partition if it can't find the default
> > boot partition.
> >
> > However, just to be on the safe side I'd boot into OS X and set it as
> > startup disk (so, yes, you can do precisely what you planned to do).
>
> These are the questions that have me wondering...

Good. Thinking is always a good thing to do before acting!

> > PS Where is the yaboot boot partition? On the YDL HD or the Mac OS X
> > HD?

> exactly! If it's on the Mac OS X disk will it interfere with using the
> Mac as a Mac only? Isn't yaboot the tiny piece of software that gets
> stuck in the MBR?  If  it's on the Mac  hdd  I would expect it to
> continue offering me a choice of  booting into Mac or Linux even after
> the Linux  disk  is nowhere to be found!

Ok, quick lesson in Mac booting conventions (I don't guarantee that I
will use the correct terminology in all cases, but it'll be "close
enough").

1. The Mac's PRAM stores a pointer to the default boot partition. If
it doesn't have a default boot partition stored in PRAM* (e.g. after a
PRAM reset) then the Mac will default by trying to boot the "first"
bootable partition on the first bootable device. If it doesn't find a
bootable partition in the first partition your Mac will continue to
try booting every subsequent partition and if it runs out of
partitions on the first device will do the same thing to all other
devices attached to your computer.

*i.e. you reset the PRAM by holding down command-option-P-R at boot
time (and heard a second chime)

2. You can set the default boot device TO A MAC OS-containing
partition using the Mac OS X Startup Disk Preferences Pane found in
the System Preferences application. You CANNOT set a non-Mac OS
partition to be the boot partition using the Mac OS X Startup Disk
Preferences Pane!!!

NOTE: If you set a Mac OS X partition to be the Startup Disk you will
LOSE the ability to boot using your yaboot bootloader until you use
the YDL CD and ybin (see instructions at terrasoftsolutions.com) to
set the yaboot bootloader partition as your startup disk (i.e. startup
partition).

3. The yaboot bootloader is effectively a bootable partition, just
like all your Mac OS containing partitions.

4. There is one situation in which you can regain the use of yaboot
after having set a Mac OS partition to be the startup disk using the
Startup Disk preferences pane: if your yaboot boot loader is the
_first_ real partition on your HD then resetting the PRAM will reset
the default startup disk pointer to point to the yaboot partition.

NOTE: there are always a few non-data partitions on a Mac disk and you
should NEVER manually mess with those unless you REALLY, REALLY,
REALLY know what you're doing.


As for your expectation that yaboot will "continue offering me a
choice of booting into Mac or Linux even after the Linux disk is
nowhere to be found!"

Yes, IF AND ONLY IF the yaboot is installed as a partition on the Mac
OS HD. HOWEVER, yaboot is PROBABLY installed with the YDL install on
your Linux HD!

I don't know the first thing about PC clones and your references to
mbr probably mean something in that world but I don't think the mbr
concept applies to Mac booting.

Basically Apple (and other PPC vendors) use a class of software called
OpenFirmware. This hardcoded software initializes basic services for
the computer and takes care of determining which partition gets to
control loading.

If a Mac OS X partition gets to boot then the computer just boots Mac
OS X. If yaboot gets to boot first, yaboot then decides whether to
boot a Mac OS X or whether to act as a bootloader for Linux.

Notes:
1. You can set a different default OS to boot with yaboot, i.e.
instead of defaulting to boot to Linux you can have the default be OS
X and the alternate be Linux (that's what I do on my Mac mini with
Ubuntu).

Back to your expectation again...

The way yaboot gets installed is with Linux. On Mac HDs you normally
create a partition alongside your Mac OS X partition using the
conventional Mac OS X formatting utility (if you want a dual boot on a
single drive) or you create a single "partition" using the Linux
formatter if you want to have one OS per HD.

The Linux installer then subdivides that "mega" partition into smaller
Linux partitions (i.e. /, /home, /tmp, etc.), the first of which is
_usually_ a small 1 MB yaboot partition that is HFS(+) format to allow
the Mac's OpenFirmware to load the yaboot bootloader. This is probably
what happened in your install!

Thus, to remove Linux, all you have to do is (a) set Mac OS X as the
startup disk using the System Preferences Startup Disk Preferences
Pane and (b) physically remove the Linux HD.

PS The reason I suggest step (a) first is that it makes sure that Mac
OS X will boot (it probably would anyway, but, given that you've had
problems you may as well be safe than sorry).

> > Also, what do you mean with set OS X as your boot disk? Do you
> > mean to set it as the default yaboot boot partition or the default Mac
> > startup disk?
> >
> >
> Right now yaboot will boot through to YDL unless I type "x" when yaboot
> appears. That suggests to me that yaboot is on the Mac disk because
> sometimes that's where the whole process stops...I suspect because they
> YDL disk can't be found!

Here's what you might want to do (and post the results to the forum):

Either from Mac OS X or from Linux fire up pdisk:

Mac OS X:
sudo pdisk -l

>From YDL:
su
/sbin/pdisk -l

This should spit out the layout of all your attached HDs.

This is my single HD:

Mac-mini:~ erdunbar$ sudo pdisk -l

Partition map (with 512 byte blocks) on '/dev/rdisk0'
 #:                type name                   length   base     ( size )
 1: Apple_partition_map Apple                      63 @ 1
 2:     Apple_Bootstrap untitled                 1954 @ 64
 3:     Apple_UNIX_SVR2 untitled             10228516 @ 2018     (  4.9G)
 4:     Apple_UNIX_SVR2 swap                   517434 @ 10230534 (252.7M)
 5:           Apple_HFS Apple_HFS_Untitled_2 67392176 @ 10747968 ( 32.1G)
 6:          Apple_Free Extra                      16 @ 78140144

Device block size=512, Number of Blocks=78140160 (37.3G)
DeviceType=0x0, DeviceId=0x0

(in Linux the HD will be at /dev/hd[a..e] instead of /dev/rdisk[0..9])

> When I say 'set OS X as my boot disk I'm referring to the "startup disk"
> as you mentioned above!
>
> When all this is done with I think I will stay away from dual boot
> systems and perhaps get myself a G3 clamshell just for YDL! I originally
> got started with YDL on a PPC 5500 with a G3 upgrade processor, but
> found YDL couldn't take advantage of the processor upgrade so the PPC
> 5500 is sitting out in the garage.

Dual boot systems are great and not at all problematic (usually). It's
possible that your G4 might need a PRAM battery replacement as well.

Hope this helps!

Eric.