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How to set the MBR?


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OK this is probably a silly question but I did not find a quick solution here on the forum.

How do I set the MBR on a disk to make it bootable.

I tried


bless --device /dev/rdisk0 --setBoot


It exits silently (I also tried the partition devices but then I got errors).


bless --getBoot returns

"Can't access "efi-boot-device" NVRAM variable


(NVRAM, isn't that where the BIOS stores its stuff? I certainly don't want OSX to write there!)


Anyway, I still get the "Error loading operating system" on boot, when I try booting from that disk. The disk is an external USB drive. I can boot into the system by adding an external USB DVD with the install dvd in it. IDE doesn't work on my system (ASUS P5B with JMicron ATA + IHC8 RAID = no bootable drive). I'm OK with the USB drive for now if I can get rid of the DVD drive. For that I need a working MBR.

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If you want to boot from your os x drive, you'd have to load with install dvd then start Terminal under utilities


type in---->

diskutil list

find your hard drive and the disk number usually rdisk0


next start fdisk


fdisk -e /dev/rdisk0


now you want to see a list of your partitions




now you want to make the partatition active (one with the HFS+ setting) notice the partition number



f 2


now you want to write the mbr





for yes, and exit by typing


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