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I have a Mac Pro 2,1 2x6-Core Xeon@2.66 GHz and am trying to boot from several ISO images written to USB sticks. I have tried the dd-based methods as recommended by Ubuntu, with no luck. In every case the stick fails to be recognized at boot time. I have also tried booting from a rEFIt CD (which I can do) but the loader there doesn't identify the USB stick in the front of the machine.

Is it possible the MacBooks are so different from the Mac Pros that these instructions wouldn't apply? Does anyone have a reproducible method for creation bootable USB sticks on a Mac Pro and then booting from them?

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Try selecting those volumes from a running mac to "bless" the volumes after the data is written. The manual page for bless will show you the syntax to run it after dd if desired. –  bmike Aug 5 '11 at 1:06
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2 Answers 2

up vote 2 down vote accepted

If your volume isn't showing in the Startup Manager but is showing in the startup disk preference pane, then it's likely the image just needs a Folder Mode bless.

This will modify that filesystem on the USB drive to ensure that other macs see it as ready to go when booting with option pressed to get to the startup manager.

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This is a huge help - I'll start here. Thank you! –  fbrereto Aug 5 '11 at 20:24
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I don't know much about booting Linux on a Mac, but you should be able to start up with the option key. It may take awhile to start up, but you should get a screen that allows you to choose what disk to boot from. Hope that helps!

EDIT: Check out this Apple Support Doc here.

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Daviesgeek is correct - the option key enters the startup manager. The mac scans all available network ports for boot servers, all busses for drives with blessed volumes get checked and all the OS that meet the minimum requirements will be shown visually on the grey screen. –  bmike Aug 5 '11 at 1:04
    
@bmike: The Ubuntu distro is an ISO9660 image, which when burned to a CD works fine. What I'd like to know is how to get such images to work on a USB stick? What does it take to bless an ISO9660 image on a USB stick? If it can't be done with the image as-is, what would it take to bless it? –  fbrereto Aug 5 '11 at 18:17
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Bless has 6 modes - but the one you want is Folder Mode. That modifies the file system permanently so when it gets burned or copied perfectly, it still looks "tasty" to the startup manager. The other modes work on NVRAM of the current mac. The man page is great. developer.apple.com/library/mac/#documentation/Darwin/Reference/… –  bmike Aug 5 '11 at 18:29
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