You can change the partition type with GPT fdisk. If not, make the appropriate corrections to the -b and -s options. Sudo gpt add -i 1 -b 40 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk1īefore entering type above commands, make sure your start and size entries are 00, respectively. You should enter these commands from the bootable USB backup clone of your boot drive. In your case, you would substitute disk0 for disk1. To correct this, I entered the following commands.

Below is the output from the command diskutil list /dev/disk1. I recreated your problem using a 4 GB flash drive. I have found information about other possible ways to set the GPT partition type through Google searches, but all the other methods seem risky, with warnings about erasing the partition in question, etc. I tried to update the partition type using the 'asr adjust' command as outlined at, but it doesn't work and gives me a very unhelpful error message: $ sudo asr adjust -target /dev/disk0s1 -settype EFIĪsr: Volume adjustment failed: Unknown error: -123 My system boots just fine, but it appears to be loading the bootloader (Clover in this case) from the /Users drive (disk1) instead of from the boot SSD (disk0), and I think the incorrect GPT partition type is to blame. On all other drives in my system, including my Carbon Copy Cloner clone of my boot drive, the partition type is 'EFI' (see below): $ diskutil listġ: Microsoft Basic Data EFI 209.7 MB disk0s1Ģ: Apple_HFS Tims Boot SSD 498.7 GB disk0s2Ģ: Apple_HFS Tims Boot SSD Clone 511.8 GB disk4s2 The GPT partition type is 'Microsoft Basic Data'.

I have a perplexing problem with the EFI partition on my boot SSD.

Efi system partion for mac with frisk