How to boot rMBP from external disc?

When the bootable disc is connected to your MacBook Pro with Retina Display via USB or Thunderbolkt, hold down the OPTION/Alt key right after the startup chime and select the item you want to boot from.

Mac OS X keyboard shortcuts

aware said:

Hi, i tried your method but rMBP only shows the option of boot from hd and boot from recovery. It does not show the external drive?

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What is on the disc in the external drive then?

aware said:

DMG image. It is a diagnostic tool.

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How did you burn the DMG? DMG files are not bootable, thus just burning the DMG as a file to a CD or DVD will not work getting a bootable disc.

Steps 7 and following should help you getting a bootable DVD: How To Make Copies of DVDs

aware said:

Hi, there are some steps i don't understand. Step 3 ask us to create new image from disc, the pic shown is for dvd but mine is downloaded dmg file. Should i create a new image from dmg? If i create a new image, what format and partitions should i choose?

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That is why I mentioned, that step 7 and following are the steps helping in your case. Maybe I should have clarified, that steps 1 to 6 can be ignored.

aware said:

Step 7 ask us to select a DVD disk image (.cdr) from column list on the left of the Disk Utility window, but mine is a dmg image. So i just burn dmg or do i need to convert to cdr?

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Further into that sentence it also teils you can Open an external image, it does not need to be a DMG.

Hi ,

I too have a question , maybe someone would help. :

So when you extract the “InstallESD.dmg” , then copy > then paste to "Source"
to make it bootable ( USB Flash Drive ).

Now is where I get confused , I have not done any of this yet , but buying any Mac and not "optimizing" it seems like a waste __ IMO.

So , now I have my USB F/D at the ready and my computer is OFF ( I go grab a cup-of-joe ) , then I plug the USB f/d into a USB port.

Here is where I`m stuck !! , I know stupid me , but what keys do I press to allow the USB drive to boot ?

If I did this I would need to get back to disc utilities to re-format the main drive and do a custom install.

Any and all help would be greatly appreciated , thanks in advance.

In the "old days" you could just but your install disc in and hold the "C" key,
then go to D-U to reformat and clean install.

Take care , Happy Holidays

Gary 

Jedi said:

Here is where I`m stuck !! , I know stupid me , but what keys do I press to allow the USB drive to boot ?

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The OPTION key.

aware said:

Sorry but i don't understand, what external image? I only got dmg file.

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The DMG is an image, a Disk ImaGe, that is the one you select.

Thanks , the Option Key

More later

Gary 