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I'm curious about the installation procedure used when you Dual Boot two versions of OS X.

From what I understand, when you install a fresh OS X system the installer copies all the required files across (from the installation DVD in this case) to the filesystem, and then "does some stuff " to make the installation bootable and appear on the boot screen when you hold down the Option key. What exactly (in all the lovely/gory UNIX/Darwin detail) is this "stuff "?

My situation is this: I have two fully working OS X installations on two laptops. I would like to transfer the 2nd installation across to the 1st laptop and dual boot the two installations on that first laptop instead. I therefore figure I could copy (dd?) across everything from / on the 2nd installation into a new HFS+ partition on the 1st laptop. Then somehow I ask the system to make that partition bootable so it will show up in the boot menu. How can I do this?

I appreciate there are two questions there but I assume (perhaps incorrectly) that they ultimately have the same answer. I have also read this SU question, but I want to do the entire process by hand, not with a 3rd party tool - more for education than utility.

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up vote 1 down vote accepted

I haven't tested this, but if you use dd to copy the entire raw volume, that should copy the boot blocks along with the filesystem contents, so nothing else should be necessary to make the volume bootable.

But I wouldn't recommend dd, as it can't cope with minor details like the source and destination volumes not being exactly the same size. It's also painfully slow unless you use the raw device entries (i.e. /dev/rdiskN instead of /dev/diskN).

Instead, I'd recommend the asr tool for copying the volume; it's smarter, and more adaptable. You can also use the Restore tab in Disk Utility (which actually uses asr to do the job). I'm pretty sure that asr also takes care of bootability, although it's been a while since I used it in this mode.

If whatever method you use doesn't make the volume properly bootable, I think all you need to do is bless the folder that contains the booter file, which is generally in /System/Library/CoreServices:

sudo bless --folder /Volumes/whatever/System/Library/CoreServices
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Make certain the drive is correctly formatted with a GUID partition table - See this article:

Use Disk Utility to clone your drive - See this article:

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