source: appendices/ppc/macmiscellany.xml@ 7ee33b91

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<appendix id="appendixe" xreflabel="Appendix E">
  <?dbhtml dir="appendices"?>
  <?dbhtml filename="macmiscellany.html"?>

  <title>Open Firmware and Mac issues.</title>

    <para>This appendix documents some of the features of ppc macintoshes,
    and in particular the requirements of coexisting with Mac OS's (OSX or
    the old OS9).  It is only relevant to NewWorld hardware.</para>

  <variablelist>

    <varlistentry>
      <term><emphasis role="bold">Open Firmware and blessed partitions</emphasis></term>
      <listitem>
        <para>The Open Firmware (OF) is the code in ROM or nvram which controls
        how the machine boots.  If booting automatically, it will boot from the
        first valid blessed partition it finds (this is a simplification,
        but it is adequate for normal purposes).</para>

        <para>It can only read apple filesystems (hfs, hfs+, or hfsx depending
        on the version of the firmware).  For disks under linux, the blessing
        is done by ybin when it installs yaboot (the loader) and yaboot.conf.</para>

        <para>Mac OS's have a tendency to look at other hfs{,+,x} filesystems
        on the disk, and unbless them if they do not match their expectations.
        Unblessing makes them unbootable. Fortunately, a filesystem of type
        <literal>Apple_Bootstrap</literal> can be read as hfs by the OF, but will
        be ignored by Mac OS.</para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><emphasis role="bold">Partitioning</emphasis></term>
      <listitem>
        <para>Macintoshes use their own partition format - this means that other
        machines are unlikely to be able to read or write to macintosh partitions
        (in particular, fdisk does not understand them). The format allows a large
        number of individual partitions, and the native Mac tools have a tendency
        to insert small "filler" partitions between the real partitions. Under
        linux, using more than 15 partitions can be problematic (shortage of device
        nodes), so the normal approach is to use the Mac tools to create an area
        of freespace at the <emphasis>front</emphasis> of the disk, then put the
        Mac OS partition(s) after it and (re-)install the Mac OS.  The
        freespace can then be partitioned using <command>parted</command> or the
        older <command>mac-fdisk</command>.</para>

        <warning>
        <para>The Macintosh resizing and partitioning tools are destructive and will
        delete all data when a partition is resized.</para>
        </warning>

        <para>For the Linux partitions, you will need a bootstrap partition - this
        can normally be a mere 800KB in size (the smallest hfs partition available)
        although the Fedora installer  has been known to insist on 800MB.  This has
        to be in front of the Mac OS partition.  The bootstrap is
        <emphasis>never</emphasis> mounted as a regular partition and should not
        be confused with a <literal>/boot</literal> partition.  Other partitions
        are as normal (at least one rootfs, perhaps swap, perhaps others).</para>

        <para>If you follow this advice, partition 1 will be the apple partition
        map, partition 2 will be the bootstrap at the start of the disk, the
        linux partitions will follow, and then the mac partition(s) - under OSX
        the first mac partition will be number 3, under OS9 it would have a higher
        number.</para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><emphasis role="bold">OSX or OF upgrades</emphasis></term>
      <listitem>
        <para>If the machine is dual-booted with OSX, the mac kernel or the OF
        will probably be upgraded at some point.  This appears to either unbless
        the bootstrap,  or else just point the OF boot device to the mac partition
        - so, the linux system will no longer be bootable.</para>

        <para>Therefore, you will need to know which partition contains the bootstrap
        so that you can boot it from OF (on an apple keyboard, hold down
        option-command-o-f (that is, alt-apple-o-f) while booting then enter a
        command like:</para>

<screen><userinput role="nodump">boot hd:2,yaboot</userinput></screen>

        <para>This will allow you to select a linux boot, and from there you
        will have to rerun <command>ybin</command>.</para>

        <para>The "OS chooser" menu that yaboot typically loads is stored in the
        OF and will not be available after a Mac kernel or firmware upgrade until
        <command>ybin</command> has been rerun.</para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><emphasis role="bold">Yaboot's requirements</emphasis></term>
      <listitem>
        <para>Yaboot is the boot loader for linux, sometimes referred to as
        the second stage loader.  It reads the yaboot.conf file on the bootstrap
        partition to find which linux system(s) should be available, and
        attempts to load the required kernel.</para>

        <para>The bootstrap man page warns that the path to the kernel should
        contain no more than one directory for reliability.</para>

        <para>Yaboot has to be able to understand the filesystem, so that it
        can find the kernel.  It understands hfs (not useful for linux, it is
        not case-sensitive), ext2 (and therefore it can read ext3), reiser3,
        and xfs.  If you want to use a different type of filesystem for '/'
        you will have to create a separate boot partition with a supported
        filesystem, and use that to hold the kernels.</para>

      </listitem>
    </varlistentry>

    <varlistentry>
      <term><emphasis role="bold">Requirements if starting from OSX</emphasis></term>
      <listitem>
        <para>Older versions of OSX (panther, leopard) can write to ext2
        filesystems using version 1.3 of ext2fsx.  The upgrade to tiger broke
        this, and version 1.4 of ext2fsx only supports reading.  Users of
        current OSX will therefore have to find some other way of creating
        a suitable filesystem and populating it, such as a Live CD or rescue CD.
        </para>
      </listitem>
    </varlistentry>

  </variablelist>

</appendix>