I tried before to make a bootable USB but it failed. When I now try to format it normally I can't. Trying this and that shows:

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *15.9 GB    disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Untitled                15.6 GB    disk2s2

MacBook: diskutil unmountDisk force /Volumes/Untitled
Forced unmount of all volumes on disk2 was successful
MacBook: diskutil eraseDisk JHFS+ Test /dev/disk2
Started erase on disk2
Unmounting disk
Creating the partition map
Error: -69877: Couldn't open device

2 Answers 2

  1. Unplug your usb stick
  2. Restart your mac
  3. Download gdisk from https://sourceforge.net/projects/gptfdisk/files/latest/download
  4. Double click the package and install gdisk.
  5. Then open up your terminal and type diskutil list
  6. Find the usb disk that you are trying to erase (/dev/diskx)
  7. Unmount the disk you are trying to erase with diskutil unmountDisk force /dev/diskx
  8. type use gdisk on the disk you want to erase. sudo gdisk /dev/diskx
  9. Once in gdisk, type x for expert command and press enter.
  10. Type ? to verify you are in the expert menu. Look for zap (destroy) GPT data structures and exit
  11. Type z
  12. When asked if you would like to delete the MBR partition also, type YES and hit enter.
  13. Gdisk will now erase your GPT and MBR and tell you it is now okay to reformat in disk utility or another partitioning utility. Do so, and let us know if you can now format your disk.


  1. Unmount the disk you are trying to erase with diskutil unmountDisk force /dev/diskx
  2. Use the DD command to erase your USB stick with zeros by entering sudo dd if=/dev/zero of=/dev/rdiskX bs=1m, where diskX is the usb disk you want to erase. This will take a long time. Please be patient.

FINALLY IF THAT DOESN'T WORK... Create a linux live cd like linux mint, and boot from it. Then use gparted to erase and format your usb.

IF NONE OF THESE WORK... Then your usb stick is most likely bricked and has hardware failure. Throw it out.

  • i try the both and not working Apr 9, 2020 at 16:01
  • Then your usb stick most likely has a hardware error and you have bricked it.
    – DanRan
    Apr 9, 2020 at 22:48

I think you need to get rid of the EFI partition first. I did it once on Windows, following these instructions:


Now, with native mac tools, I think a combination of diskutil to unmount the volume (disk2s1 in your case) and gpt to remove the EFI partition would do the job, but so far I did not succeed on my test key.

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