This question, possibly the same question, has been asked: http://apple.stackexchange.com/questions/224752/couldnt-open-device

However, my question hopefully demonstrates a more specific scenario as the situation in which caused the error explicitly known:


The following done as a root user:

1. I plugged in my SD card and ran `diskutil list` to grab the internal device node (/dev/disk2)
2. I ran `diskutil partitionDisk /dev/disk2 GPT UFSD_EXTFS4 New 100%` (UFSD_EXTFS4 is ext4 provided by Paragon)
3. I saw that it was working, so I interrupted the process at step 2.
4. I attempted to rerun the command with the number of partitions explicitly stated `diskutil partitionDisk /dev/disk2 1 GPT UFSD_EXTFS4 New 100%`

I get the message: 

    Started partitioning on disk2
    Unmounting disk
    Error: -69877: Couldn't open device

Running `gpt show -l /dev/disk2` yields

    start     size  index  contents
        0  7741440

Running `gpt destroy /dev/disk2` yields

    gpt destroy: unable to open device '/dev/disk2': Permission denied

It seems to me there is some lock on device disk2. I just need to figure out how to release it.

I was able to release it by rebooting into safe mode (holding shift key during boot) and then rebooting back into normal mode. I would like to know, however, what exactly could be done to release this lock without rebooting.