Unmounting external drives on a Mac is usually done quick and simple by either dragging drive icon to the trash, or by using the eject symbol in a Finder window. Mounting usually happens automatically when a new drive is inserted into a USB port or SD card slot.
However, there is a way to do this via the command line, of which I am a big fan. Fire up a Terminal session and see how to do it.
Listing available drives
To see what’s currently attached to your Mac, let’s use the diskutil command, followed by the word list. You’ll see output like this:
diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *512.1 GB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_HFS Macintosh SSD 511.3 GB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3 /dev/disk1 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *1.0 TB disk1 1: EFI EFI 209.7 MB disk1s1 2: Apple_HFS Mac HDD 1TB 999.9 GB disk1s2 /dev/disk2 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *1.0 TB disk2 1: Apple_HFS VM Drive
Attached drives are listed with their physical locations on the left (i.e. /dev/disk0, /dev/disk1, etc), as well as with their respective partitions if available on the right (like disk0s1, disk1s2, etc). Make a mental note of the latter: you’ll see that we have a physical disk (like disk0), on which several partitions may have been created. It is those partitions we’ll mount and unmount, NOT the physical drive.
Unmounting an attached hard drive
On my system I have two internal hard disks (disk0 and disk1), and one external USB drive (disk2). Let’s unmount that USB drive now:
diskutil unmount /dev/disk2s1 Volume VM Drive on disk2s1 unmounted
Note how we use the unmount command. We need to specify the location of the partition with its full path (i.e. /dev/disk2s1).
Mounting an attached hard drive
To mount the drive again, without having to take it out and plugging it in again, I can issue this command:
diskutil mount /dev/disk2s1 Volume VM Drive on /dev/disk2s1 mounted