How to make a Mac harddrive partition non bootable

Question

Just recently added an SSD drive replacing the optical drive. Carbon Copy the whole partition and now left with 2 bootable drives. How do I make the old partition no longer bootable? I've changed the default boot using Startup Disk utility, but want to make the partition completely non bootable

Thanks

Answer 1

Your SSD drive may already be non bootable. Let's suppose your SSD drive is mounted in /Volumes/SSD. Then open a Terminal (in Applications>Utilities) and type:

bless --info /Volumes/SSD/

If the output looks similar to this:

finderinfo[0]:      0 => No Blessed System Folder
finderinfo[1]:      0 => No Blessed System File
finderinfo[2]:      0 => Open-folder linked list empty
finderinfo[3]:      0 => No alternate OS blessed file/folder
finderinfo[4]:      0 => Unused field unset
finderinfo[5]:      0 => No OS 9 + X blessed X folder
64-bit VSDB volume id:  0x844F837C9317318A

the drive won't be able to boot.

As a comparison, this is what the output for a bootable drive would look like:

bless --info /

finderinfo[0]:     62 => Blessed System Folder is /System/Library/CoreServices
finderinfo[1]: 327769 => Blessed System File is /System/Library/CoreServices/boot.efi
finderinfo[2]:      0 => Open-folder linked list empty
finderinfo[3]:      0 => No alternate OS blessed file/folder
finderinfo[4]:      0 => Unused field unset
finderinfo[5]:     62 => OS X blessed folder is /System/Library/CoreServices
64-bit VSDB volume id:  0xD9A24BFA7A5E7EDC

The command bless includes option --unbless to unset volume bootability (from man bless):

--unbless directory Use the HFS+ volume mounted at directory and unset any persistent blessed files/directories in the HFS+ Volume Header.

So if you find out in the output above that your drive is bootable, "unbless" it:

sudo bless --unbless /Volumes/SDD/