unmountDisk

UnmountDisk is a subcommand of Apple's diskutil utility. It unmounts all mounted volumes on a specified disk, allowing the device to be safely prepared for removal or reconfiguration. Unlike detaching a disk, which disconnects the device from the kernel, unmountDisk only unmounts the filesystem volumes while the device node remains present in the system.

Usage: The command typically takes a disk identifier such as /dev/disk2. The basic form is: diskutil unmountDisk /dev/disk2. If volumes are in use, diskutil may fail to unmount them; the force option can be supplied to force unmount all volumes that are mountable, for example: diskutil unmountDisk force /dev/disk2. After a successful unmount, all volumes on the disk are unmounted, and the disk is safe to physically remove or to perform further operations such as repartitioning.

Relation to other diskutil verbs: diskutil also offers unmount (for a single volume) and detachDisk (to detach the disk from the system). The unmountDisk command is particularly useful when a disk contains multiple partitions that must be unmounted simultaneously.

Limitations and notes: If a process holds a file on any of the volumes, unmountDisk may fail until the process releases it. The command does not always guarantee immediate removal of the device; on some configurations the kernel may still have references. It is primarily a macOS Disk Utility CLI feature; Linux or other platforms have different tooling and syntax for unmounting disks.