HOWTO-Booting with Yaboot on PowerPC
Chapter 9 - Recovering From Misconfiguration

If you have a problem booting, don't panic. Yaboot can boot any installed Linux kernel and system from the boot: prompt.

9.1 Resetting the NVRAM

Hold the Command-Option-p-r keys all together at startup to reset all nvram parameters to their factory defaults. Hold the keys until you hear the startup chime two or three times. If the setup recommendations were followed, the yaboot installation will be be the first bootable partition and OpenFirmware will boot it automatically. It should be noted that MacOS settings such as virtual memory, startup disk, and screen resolution will also be reset to their defaults.

9.2 Loading Yaboot

If a boot: prompt isn't presented, then yaboot isn't being loaded. You can load it manually from OpenFirmware. Holding the Command-Option-o-f keys all together after pressing the power-on key will give you an OpenFirmware prompt

         0 >

(Command is the key with the cloverleaf and/or apple engraved on it).

At the OF prompt, you will need to use OpenFirmware paths for most of the boot configuration items. You can determine most OpenFirmware paths from the OF prompt using a few OF commands, then construct an OF boot command to directly boot your kernel.

The full OpenFirmware path consists of three parts in the format

         device-name:partition-number,/filesystem-path

The OF command devalias will list all the device aliases effective on your system. You may see some of these:

       Name      Device Type
       ----      --------------------------------------------------
       hd        internal ide drive (primary controller, master disk)
       ultra1    internal ide drive (primary controller, slave disk)
       ide0      ide drive (secondary controller, master disk)
       ide1      ide drive (secondary controller, slave disk)
       cd        CD-ROM 
       zip       Zip drive
       fw        FireWire interface
       fd        Floppy drive
       enet      Ethernet interface

Append the partition number of the boot partition (in our recommendation, 2) and then follow that with ,yaboot to boot the yaboot file on the boot partition.

         0 > boot hd:2,yaboot

Hit return, and yaboot should be loaded and display its boot: prompt. If you don't know the partition number, just start at 2 and work your way up until you hit it.

9.3 Manually Loading a Kernel Image

Once you have the boot: prompt, you can enter a label defined in your yaboot.conf to boot that kernel image. Or instead of a label, you can enter a full OpenFirmware path. A typical kernel path might be

         boot: hd:3,/vmlinux

To pass parameters to the kernel, add them on to the boot: prompt line after the kernel label or path. You'll need to specify root= as a minimum, but you can add any kernel parameters desired. Here's an example;

         boot: hd:3,/vmlinux root=/dev/hda3 ro

HOWTO-Booting with Yaboot on PowerPC