Steps to boot a fresh PowerPC32 install of Debian from GRUB on installer CD

[Alex Perez <aperez@alexperez.com>]

If you've successfully gotten 32-bit PowerPC Debian installed using one 
of the recent Debian Ports snapshot CDs (I used 
https://ftp.acc.umu.se/cdimage/ports/snapshots/2020-11-09/debian-10.0.0-powerpc-NETINST-1.iso) 
but have no installed bootloader (grub install fails), here's what you 
can do to temporarily boot in to this installed environment:

1) After the install completes, re-boot _with the installation CD still 
in the drive_
2) Break in to GRUB, and type 'c' to get to a grub command line
3) Run the following commands from the GRUB CLI, substituting 
apple3/sda3 for the appropriate volume where /boot was installed to.

insmod part_apple
insmod ext2
'linux (ieee1275/hd,apple3)/boot/vmlinux root=/dev/sda3'
initrd (ieee1275/hd,apple3)/boot/initrd.img
boot
...and your machine will boot to the installed environment.

I then installed the 'git' Debian package, and cloned the yaboot4 git repo:

git clone --recurse-submodules https://github.com/rsaxvc/yaboot4

...and then compiled it with 'make'

...and then did a 'sudo make install'

...and then manually edited /etc/yaboot.conf with correct arguments:

image=/boot/vmlinux
        label=Linux
        root=/dev/sda3
        initrd=/boot/initrd.img
        read-only

...then ran 'ybin' and rebooted. And it results in a working environment.