Sometimes when you try to repartition a USB drive in Disk Utility in OS X, the “partition” option is greyed out. When this happens there is a simple CLI command that will fix the issue.
First identify which disk is mounted by looking at the details in Disk Utility. Then modify the “diskX” in the command below replacing “X” with the number of the mounted drive. I will demonstrate an example below.
Command: diskutil partitionDisk diskX 1 GPT HFS+ new disk R
In the example below, you would alter the command so that it repartitions disk2 as follows:
diskutil partitionDisk disk2 1 GPT HFS+ newdisk R
