Re: InstallESD.dmg & BaseSystem.dmg

[Jeff Gaines]

On 23/07/2011 in message <1k4vd83.ruse8aqjnn69N%me...@privacy.net> R wrote:

>And What is the purpose of the BaseSystem.dmg package? The
>installer for Snow Leopard does not contain a disk image like that.

Is it what goes in the hidden partition Lion creates for recovery purposes?

--
Jeff Gaines Wiltshire UK
If it's not broken, mess around with it until it is

[David Empson]

R <me...@privacy.net> wrote:

> The Lion installer app contains two disk images (at least). There is
> InstallESD.dmg and within that BaseSystem.dmg. Both contain
> a boot.efi file and, for example, System and Library directories.
>
> 'find' does not find 'mach_kernel' in BaseSystem.dmg, when the
> latter is mounted. But the commonly used method for creating a
> VMWare Lion installer doesn't copy 'mach_kernel' from the root
> directory of the mounted InstallESD.dmg. And yet, sure enough,
> when Lion is installed in a VM 'mach_kernel' is there in '/'. So
> where does it come from?

>
> And What is the purpose of the BaseSystem.dmg package? The
> installer for Snow Leopard does not contain a disk image like that.

BaseSystem.dmg is a compressed disk image that contains the OS and
applications used by the Lion Recovery volume. They are also used if you
boot from InstallESD.dmg (burned to DVD or written to a USB flash
drive).

The only obvious difference between InstallESD.dmg and the Lion Recovery
volume is the latter is missing the installer packages for Lion.

From a quick glance, it appears that the process works like this:

1. EFI boots from the system on the volume to which InstallESD.dmg has
been copied (or the Lion Recovery partition). This involves boot.efi and
mach_kernel.

2. Something early in the boot process mounts BaseSystem.dmg at / and
transfers control to the next stage of the boot loader on that volume.
The real volume is remounted on a different drive, so it is still
accessible. mach_kernel might be getting copied after that point.

3. BaseSystem.dmg takes over and presents the user interface for the
utilities, or starts installing Lion automatically.

I'm not sure how the automatic installation is handled, nor how it deals
with getting the install packages from a different drive - must be
something like a soft link or alias, or perhaps something passed in via
NVRAM.

BaseSystem.dmg is in the order of 2 GB expanded, so using a compressed
disk image saves a lot of space for the recovery partition.

--
David Empson
dem...@actrix.gen.nz