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bless is the command used on Mac OS X to make volumes bootable.
This page discusses the bless command and its applicability in a PureDarwin system.
It is a work in progress; please contribute.

What is bless

bless is a command line tool on Mac OS X and Darwin to make volumes bootable.
It also includes libbless, a library which is used by other applications (such as installers) to make volumes bootable.
The bless project is available as Open Source from Apple.

"Worlds" supported by bless


The bless command is used to set up the "efiboot" boot loader on Intel-based Macintosh systems which use EFI as their firmware.
(to be written)


The bless command was used to set up the "boot" boot loader on generic BIOS-based systems in older versions of Darwin.

bless-24 was known to work with BIOS-based machines.
It appears that bless-37.1.4 from 2006 was the latest version that contained BIOS code.
Later versions of bless are no longer capable of blessing a volume so that it works on BIOS-based machines.
 *  Revision 1.21  2006/01/02 22:27:28  ssen
 *  <rdar://problem/4395370> bless should not support BIOS systems
 *  For RC_RELEASE=Leopard, keep BIOS support, but preprocess it out
 *  for Herbie and the open source build
(Maybe the BIOS-related portions of the code should be patched back in by PureDarwin.)

(to be written)


Was used to set up the "BootX" boot loader on "New World" and "Old World" PowerPC computers which used OpenFirmware as their firmware. Not relevant for PureDarwin.

Using bless

The usage of the bless command varies depending on which "world" you are targeting. Please refer to the bless manpage that comes with the bless command.

bless alternatives

A method to make a disk bootable on BIOS and EFI machines without using the bless command is described on the boot page.