I am willing to dual-boot my MacBook Pro (13-inch, Early 2011) macOS Sierra to install Ubuntu.

I am having some trouble with my USB flash drive when I try to erase it using Disk Utility. It says "Couldn't open device". (as shown below)

Please help me ASAP!

enter image description here


Open Terminal, and type

diskutil list

/dev/disk4 (external, physical):


0: FDisk_partition_scheme *8000.1 GB disk4

1: 0xEF 12.3 MB disk4s2

It cannot display the USB. To erase the USB completely, run:

diskutil eraseDisk free EMPTY /dev/disk4
diskutil list

/dev/disk4 (external, physical):


0: GUID_partition_scheme *8.1 GB disk4

1: EFI EFI 12.3 MB disk4s1
  • diskutil eraseDisk free EMPTY /dev/disk2 diskutil list Unknown partition scheme: /dev/disk2 – kipbits Feb 17 at 1:22

The first thing I would try is restarting your MacBook Pro in Safe Mode and trying to erase the USB flash drive then.

To start in Safe Mode:

  1. Fully shut down your Mac
  2. Restart your Mac
  3. Immediately press the Shift key and keep it down
  4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
  5. After booting up, insert your USB Flash Drive
  6. Launch Disk Utility and try erasing the USB Flash Drive
  7. To exit Safe Mode just restart your Mac as normal

If this does't work, take a note of any error messages and report back.

  • did not work for me, diskutil eraseDisk JHFS+ Untitled /dev/disk2 Error: -69877: Couldn't open device – kipbits Feb 17 at 1:29
  • Getting error in disk utility, Couldn't Open device – Stivan May 23 at 14:19
  • Didn't work for me. I tossed the flash drive. – Ben Creasy Sep 22 at 4:50

I concur try rebooting.

I got around the issue myself trying to format an old PATA 80 GB drive to work with a truly old 2004 G4 Macmini: I had to try a few times but from memory what worked was to format the partition exFAT temporarily, then "erase" the whole disk choosing a new partition scheme from: - Apple (powerpc) - GUID (intel) - Master Boot Record (Windows)

The PowerPC macs use "Apple Partition Scheme". Perhaps ejecting or unmounting first helps.


I was getting this same error and discovered that the MicroSD Adapter I was using had a read-only switch enabled. Toggling the read-only switch off resolved the problem.

  • Doesn't really apply here since the Cruzer Edge has no read lock, but yeah, also with full sized SDs there's the same lock. – JMY1000 Jan 14 '18 at 22:06

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