Bless an HFS or HFS+ Boot File with grub-macbless

You will finish with the correct grub-macbless command for a mounted HFS or HFS+ volume, using either the PPC or x86 mode. This is a boot metadata operation, not a general-purpose file copy.

Allow about 10 minutes if the volume is already mounted and you know the file or directory to bless. You need the grub-common package, a readable HFS or HFS+ volume, and a path on that volume. The examples below use placeholders because the right path depends on your disk layout.

The local system used for this guide has GRUB 2.12-1ubuntu7.3, supplied by grub-common. Check your own installation before relying on the examples.

1. Check the installed command

Start with the version and help output. These commands only read local program information:

$ grub-macbless --version
grub-macbless (GRUB) 2.12-1ubuntu7.3
$ grub-macbless --help

The version line will differ on another distribution. The installed synopsis is grub-macbless [OPTION...] --ppc PATH|--x86 FILE. That distinction matters: PPC mode takes a path, while x86 mode takes a file.

2. Confirm the target volume and path

Identify the mounted volume and inspect the candidate path without changing it. Replace the placeholder with the mount point you have deliberately selected:

$ findmnt --target /mnt/MAC_VOLUME
$ ls -ld /mnt/MAC_VOLUME/PLACEHOLDER_PATH

findmnt is a useful boundary check: it helps catch a typo that would otherwise point at an ordinary Linux directory. The second command confirms that the path exists from Linux's point of view. The manpage does not define a special placeholder, default path or automatic volume discovery, so supply an explicit path every time.

Use the path exactly as it appears on the mounted filesystem. Quote it if it contains spaces:

$ ls -ld '/mnt/MAC_VOLUME/Library/PLACEHOLDER FILE'

3. Choose the Mac architecture

Choose one mode from the two documented operations. Use --x86 for an Intel-based Mac boot file:

$ sudo grub-macbless --x86 /mnt/MAC_VOLUME/PLACEHOLDER_BOOT_FILE

Use --ppc for a PowerPC-based Mac and provide the relevant path:

$ sudo grub-macbless --ppc /mnt/MAC_VOLUME/PLACEHOLDER_BOOT_PATH

The local manpage describes the command as blessing a Mac file or directory on HFS or HFS+. It does not say that the two modes are interchangeable. Do not select a mode from the machine running the command alone: select it for the Mac firmware and boot arrangement that will use the volume.

sudo is shown because mounted system volumes often require elevated access to update filesystem metadata. It is not a substitute for checking the target. If your account can perform the operation without elevation, omit sudo. Review the path displayed in your shell before accepting a privilege prompt.

4. Treat the operation as a metadata change

There is no dry-run, backup, unbless or undo option documented for grub-macbless. Blessing changes boot-related state on the target HFS or HFS+ volume. This is not normally destructive to the file contents, but a wrong target can alter the boot choice for the wrong installation.

Before running it on a recovery or production disk, make sure you have a usable backup or image of the volume. If you selected the wrong file or volume, stop using that volume as a boot source and restore the intended boot metadata from your backup or rerun the command against the correct, known-good target. Do not invent an inverse command: the installed manpage documents only --ppc, --x86, --verbose, help, usage and version options.

5. Capture the result

For a script or a change record, capture the command's status immediately. Add --verbose when you need the program to print progress or diagnostic messages:

sudo grub-macbless --verbose --x86 /mnt/MAC_VOLUME/PLACEHOLDER_BOOT_FILE
status=$?
printf 'grub-macbless exit status: %s\n' "$status"
exit "$status"

Keep the exact command, GRUB version, target mount point and selected architecture in your change record. A successful command invocation is not proof that the firmware will boot the result. The machine may have other requirements, including the right filesystem support, firmware mode and a complete bootloader installation.

If the command reports an error, do not retry with the other architecture as a reflex. First check the mount, path, filesystem type, permissions and the target's intended firmware. Use grub-macbless --usage or grub-macbless --help to confirm the options provided by your installed build.