How to set the MBR?

[MacFeast]

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.

[xtreme571]

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

 

p

 

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

and enter f PARTITIONNUMBER

 

f 2

 

now you want to write the mbr

write

 

hit

Y

for yes, and exit by typing

exit