b0 error when installing Mac OS X

So you’ve installed Mac OS X, the computer has restarted, and you’re left with the following when the computer tries to boot from the hard drive:

b0 error

What does this mean? Simply that the partition isn’t active. Why the MacOS installer doesn’t automatically set the partition as active (especially when it’s the only partition) puzzles me. Maybe it has something to do with me installing OS X on a PC. Regardless, here is a fix I came across here.

There are a lot of people who experience a b0 error on their first boot up after installation. Or the bootloader immediately takes them back to the Windows installation (on dual boot).

These people probably forgot to set the MacOSX partition “Active”

A common mantra provided here to newbies for setting up for installation is:

  • Make the partition Primary
  • Make the partition ID=AF (signifies an HFS partition)
  • Make the partition Active

There is a built-in Unix utility in MacOSX that can be used to set your partition “Active”. It is called Fdisk

Setting Your Partition “Active” Using Fdisk

Words in bold below are things you must type (followed by Enter).

1. Boot your Mac OS X install dvd
2. Once the installer is running, go to the Utilities menu and open Terminal

3. Determine which disk your MacOSX partition is on

Type diskutil list

Verify which disk number holds your partition (disk0, disk1, etc.)


4. Start using Fdisk

Assuming the MacOSX disk is the first disk (“disk0”), then
type fdisk -e /dev/rdisk0 <== use “rdisk” with your disk number here !!

Ignore the error “fdisk: could not open MBR file …”


5. Determine which partition for MacOSX needs to be set “Active”

Type p

Verify which partition is for MacOSX (1, 2, 3, etc.)


6. Set the partition “Active”

Assuming it is partition 1, then
type f 1 <== use your partition number here !!


7. Save and exit

Type write

Type y (yes you are sure)

Type exit (to quit)


8. Remove the install DVD and reboot