[ previous ] [ Contents ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ next ]

HOWTO-Booting with Yaboot on PowerPC
Chapter 6 - Customizing Your Boot Configuration

To customize your yaboot installation, use any text editor such as vi or nano (or nano-tiny in the Debian installer) to edit the yaboot.conf file. If you used yabootconfig to create the initial yaboot.conf, it will already contain a basic configuration to boot the linux system.

The yaboot.conf has numerous options; see the yaboot.conf man page for details. I will briefly cover the most popular items here. The file controls both yaboot operation during the actual boot, and ybin operation while saving the configuration to the boot partition.

Lines in the file beginning with # are interpreted as comments. Each option or parameter must be specified on a separate line. Don't use any extra spaces within or following parameter definitions. Also, the file must have unix newlines; be sure to save as a unix type file if you create or edit it within Mac OS.

6.1 Linux Style Device Paths

For those unfamiliar with Linux device naming, partition paths are in the form of /dev/xxx# where xxx is the Linux device name and # represents the partition number. Typical Linux device names are:

       Name   Device Type
       ----   --------------------------------------------------
       hda    internal ide drive (primary controller, master disk)
       hdb    internal ide drive (primary controller, slave disk)
       hdc    secondary controller, master disk (often used for CD-ROM)
       hdd    secondary controller, slave disk (often used for Zip drive)
       sda    first SCSI disk (SCSI ID address-wise)
       sdb    second SCSI disk 
       scd0   first CD-ROM (or sr0)
       fd0    first floppy drive
       fd1    second floppy drive

6.2 OpenFirmware Device Paths

A utility for finding the OpenFirmware device path corresponding to a given Linux device path is provided: ofpath. ybin uses ofpath internally to convert Linux device names you use in yaboot.conf to OpenFirmware equivalents. Example: ofpath /dev/hda (should return hd:). You can also figure out OpenFirmware device paths yourself, see Recovering From Misconfiguration below.

6.3 Required Settings

The bootstrap partition is identified with boot=boot-partition, where boot-partition is the Linux-style path to the bootstrap partition. If you followed our partitioning recommendations on your internal hard disk, that would be boot=/dev/hda2.

For PowerMacs, a magicboot line such as magicboot=/usr/local/lib/yaboot/ofboot is also required. Several models cannot execute a straight ELF, and need a CHRP script (which this line in the yaboot.conf makes available).

The partition=, image=, and root= settings (under kernel image settings below) are also required.

6.4 Boot Menu Options

A CHRP script (ofboot) has been provided which ybin will modify using yaboot.conf settings, to display a very handy multi-OS boot menu.

If you are setting up a multi-OS boot menu, you'll need to identify the partitions where each OS lives. You can use Linux-style or OpenFirmware partition paths. Here are some examples illustrating the possibilities:


When using macosx=, if you have OS X installed on a UFS partition, then point the macosx to the OS X bootstrap partition, not the UFS root. Don't be tempted to use the OS X bootstrap partition for ybin, however — you still need a separate Apple_Bootstrap partition.

When using bsd=, on the other hand, point to the BSD root partition, not a bsd bootstrap partition. To use bsd=, you also need to have the bsd bootloader (ofwboot) available in /usr/local/lib/yaboot/ when running ybin.

If nothing is selected from the boot menu when it appears, the system launches yaboot to start Linux. To launch another OS when no key is pressed, add a defaultos= line, for example defaultos=macos or defaultos=bsd.

6.5 Kernel Image Settings

Kernel images to be launched by yaboot can be kept on any partition, in an ext2, ext3, XFS, ReiserFS, or HFS/HFS+ filesystem. Yaboot will need to know the kernel partition number and filesystem path.

The yaboot.conf file has two sections; most options are in the global section at the top of the file, and options pertaining to separate kernel images are grouped together below. Most kernel image options may be specified either globally or locally; a global option is overridden if it is re-specified in a kernel image section. Each kernel image section begins with an image=/ line specifying the filesystem path to that kernel image; the first image=/ line marks the end of the global section.

Yaboot must know the device, partition number, and filesystem path for the kernel image that is to be loaded and started. However, device= is usually not necessary, because if you don't specify it yaboot assumes it will find the kernel on the same device it was booted from, which is quite often true. You should always supply the kernel partition number, for example partition=3, and of course the image path (for example image=/boot/vmlinux ). If your kernel image is at the root level of the partition, don't forget to include the leading slash when specifying the image path (image=vmlinux will probably fail).

It's worth noting that yaboot locates the kernel image within a partition's filesystem without regard to where that partition will eventually be mounted within the Linux root filesystem. So, for example, if you've placed a kernel image or symlink at /boot/vmlinux, but /boot is actually a separate partition on your system, then the image path for yaboot will just be image=/vmlinux.

You must also specify the Linux partition path for the root partition, for example root=/dev/hda3. This parameter is passed to the kernel when it starts up to let it know where its root filesystem is located. Many other options are available to pass additional boot parameters to the kernel (append=), specify initial ramdisk size (ramdisk=), load a ramdisk image (initrd=), and others. Refer to the yaboot.conf man page for details on kernel image options.

Here's a simple but complete example yaboot.conf with one kernel image section:

       # Where's the bootstrap partition
       # CHRP script spec
       # Dual boot with Mac OS
       # How long to wait at the OS boot menu (seconds)
       # How long to wait at the boot: prompt (tenths of a second)
       # Globally identified root partition
       # The device where the kernel lives
       # Kernel image section begins here
       # Specify the filesystem path to the kernel image, symlinks are OK
           # Specify the partition number where this path is valid
           # Add a label, you can type this at the boot: prompt to load this kernel
           # Specify the type of root fs mounting, read-only allows fsck to run
       ## You must run ybin for changes to take effect!!!!!!!

To netboot a kernel image via tftp, use image=/tftpboot/vmlinux (the path on the tftp server) and device=enet: (substituting the tftp boot server IP address).

Normally the first image specified in the yaboot.conf will be the image booted if no entry is made at the boot: prompt. To have another image loaded by default, add a default=label line in the global section.

6.6 Optional and Cool Settings

Yaboot and your multiboot menu can throw a splash of color into your life! Use fgcolor= and bgcolor= lines to set your screen to wake you up in the morning with black, blue, light-blue, green, light-green, cyan, light-cyan, red, light-red, purple, light-purple, brown, light-gray, dark-gray, yellow, and white. Make fgcolor and bgcolor the same if you'd really like a challenge.

Add any or all of enableofboot, enablenetboot, or enablecdboot to add the respective options to your OS boot menu: boot from OpenFirmware, the network, or CDROM.

Use Set delay= (in seconds) to determine how long the multiboot OS menu should wait before booting the default OS. timeout= (in tenths of seconds) to set how long yaboot should wait at the boot: prompt for you to choose a kernel image before booting the first image in the file or the default= image.

Booting password protection is available using a password= line. When you add password=, a password will be required for all booting. Automatic booting is not possible unless a restricted line is added.

If restricted is added in the global section, kernel images defined in yaboot.conf may be booted as long as no arguments are added at the boot: prompt. This is useful for unattended booting, while preventing the instant rootshell problems of console access (though OpenFirmare passwords are also needed to make this really secure, along with locking the case). To boot an undefined image, or any image with additional arguments, a password will be required.

The password= line may either be a plaintext password or an MD5 hash (the same format as the Linux /etc/shadow file). To make an md5 hash use the following perl snippet:

         $ perl -e 'printf("%s\n", crypt("secret", "\$1\$saltstrg"))'

The saltstrg should be a random string, for example one generated by

         makepasswd --chars=8

[ previous ] [ Contents ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ next ]

HOWTO-Booting with Yaboot on PowerPC

Version 1.00, Oct 28 2001

Chris Tillman