On an Intel-based Mac: Restart your Mac, then hold down Command + R keys when the screen turns black.

So, it's reasonable to think that the error has something to do with the failure of 'Unmounting disk.' In this case, you can manually unmount the disk by executing another command. If you are formatting the drive in Terminal, you'll notice that the process macOS was running before showing the 'Error: -69877: Couldn't open device' error: 'Unmounting disk.' To change the disk's permissions on Mac, you can right-click its icon on the desktop and select 'Get Info.' If you are experiencing 'Couldn't open device.: (-69877)' on Mac when erasing a USB flash drive, (micro) SD card, or external hard drive, you need to ensure that your account has 'Read & Write' privilege to the drive.

How to fix 'couldn't open device 69877' on Mac when erasing an external disk? Like ' Couldn't unmount disk 69888,' error 69877 may be caused by the failure to unmount the disk due to it currently being used by other processes, like FileVault.īesides, 'couldn't open device 69877' may also occur when you don't have write access to the drive, or the drive is physically locked or has hardware issues. There could be many reasons why the error 'couldn't open device 69877' pops up on Mac. Why do you see 'couldn't open device 69877' on Mac? How to fix 'couldn't open device 69877' on Mac when erasing the internal disk? Guide to the error reading 'Couldn't open device.: (-69877) on Mac: Here, we will analyze the reasons behind 'couldn't open device 69877' on Mac and help you fix it with practical solutions. When erasing a disk on Mac, you may receive ' Error: -69877: Couldn't open device' in Terminal or ' Couldn't open device.: (-69877)' in Disk Utility.ĭespite the slightly different wording, the errors refer to the same 'couldn't open device' issue, which can happen on your internal hard drive or external storage device, such as a (micro) SD card, USB flash drive, external hard drive, etc.

Erasing disk failed mac