Why change the type code of a hard disk partition? Here’s how it all started.

Ventoy is an open source tool to create bootable USB drive for ISO/WIM/IMG/VHD(x)/EFI files. There is a problem, when it create an EFI partition.

But there’s a problem, Ventoy creates an EFI partition, formatted as FAT16, and the partition type code is 0700 (correctly it should be EF00). On macOS, since the EFI partition is automatically mounted, if two USB flash drives are inserted at the same time, the second one will not be mounted correctly.

After doing some searching, I chose GPT fdisk. It is open source software (GPL) and cross-platform, supporting Linux, macOS, Windows.

Preparation Tools

For macOS, download gdisk-1.0.10.pkg. Once installed, you can use gdisk with root privileges.

# /dev/disk2 is the target disk
sudo gdisk /dev/disk2

Command ? for help.

Command (? for help): ?
b	back up GPT data to a file
c	change a partition's name
d	delete a partition
i	show detailed information on a partition
l	list known partition types
n	add a new partition
o	create a new empty GUID partition table (GPT)
p	print the partition table
q	quit without saving changes
r	recovery and transformation options (experts only)
s	sort partitions
t	change a partition's type code
v	verify disk
w	write table to disk and exit
x	extra functionality (experts only)
?	print this menu

Change Disk Partition Type Code

The specific steps are as follows.

  1. p print the partition table (To confirm you have select the right disk)
  2. t change a partition’s type code.
  3. Enter 2. It needs to be entered as appropriate.
  4. Enter partition type code ef00. ef00 is for EFI,enter L to list partition types.
  5. p print the partition table (Make sure the changes are correct).
  6. w write table to disk and exit.
  7. y Confirm to proceed.

The modification is completed.

An example of the operation is shown below.

sudo gdisk /dev/disk2

Command (? for help): p
Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048       976707591   465.7 GiB   0700  Ventoy
   2       976707592       976773127   32.0 MiB    0700  VTOYEFI

Command (? for help): t
Partition number (1-2): 2
Current type is 700 (Microsoft basic data)
Hex code or GUID (L to show codes, Enter = 700): ef00
Changed type of partition to 'EFI system partition'

Command (? for help): p
Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048       976707591   465.7 GiB   0700  Ventoy
   2       976707592       976773127   32.0 MiB    EF00  VTOYEFI

Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING

Do you want to proceed? (Y/N): y

OK; writing new GUID partition table (GPT) to /dev/disk2.

Hard Disk Selection Methods for Operating Systems

# N for disk number

# macOS
gdisk /dev/diskN

# Windows
# Terminal needs to be executed in administrator mode.
# PhysicalDriveN,N for disk number,start from 0.
gdisk64.exe \\.\PhysicalDriveN

# Linux
gdisk /dev/sdN

# FreeBSD
# adN or daN
gdisk /dev/adN