I was able to boot from my external HD formatted in Mac OS Extended until I partitioned it with Disk Utility. According to Disk Utility the Mac partition is still bootable but the drive no longer shows up in Select Startup Disk or when I reboot the Mac with option key. Is there a way to make it show up as a bootable disk again without having to reformat it? I'm using OS10.9.5
Below is the output from diskutil list.
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 499.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_HFS Samsung Mac 251.1 GB disk1s2
3: Apple_Boot Recovery HD 650.0 MB disk1s3
4: Microsoft Basic Data Samsung PC 248.1 GB disk1s4
Information from sudo blessed for the external HD:
finderinfo[0]: 152860 => Blessed System Folder is /Volumes/Samsung500/System/Library/CoreServices
finderinfo[1]: 592373 => Blessed System File is /Volumes/Samsung500/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]: 152860 => OS X blessed folder is /Volumes/Samsung500/System/Library/CoreServices
64-bit VSDB volume id: 0x2BD688998DF36E9A
Thanks for your help
diskutil listto your question. – David Anderson Jul 28 '18 at 18:17sudo bless --info <mount point of external drive>? (For example:sudo bless --info /Volumes/ExternalHD) – jaume Jul 29 '18 at 11:33