The
bless command, which can be run from a Terminal window,
can be used to determine the boot disk on an OS X system:
$ bless --info --getBoot /dev/disk0s2
If you are interested in more details for that drive, you can use the
diskutil info command followed by the drive's designation.
E.g.:
$ diskutil info /dev/disk0s2 Device Identifier: disk0s2 Device Node: /dev/disk0s2 Part of Whole: disk0 Device / Media Name: Customer Volume Name: Macintosh HD Escaped with Unicode: Macintosh%FF%FE%20%00HD Mounted: Yes Mount Point: / Escaped with Unicode: / File System Personality: Journaled HFS+ Type (Bundle): hfs Name (User Visible): Mac OS Extended (Journaled) Journal: Journal size 24576 KB at offset 0x1119b000 Owners: Enabled Partition Type: Apple_HFS OS Can Be Installed: Yes Media Type: Generic Protocol: SATA SMART Status: Verified Volume UUID: A140B2C6-4C4F-3B14-B179-C1A7FE0325D4 Total Size: 249.2 GB (249199599616 Bytes) (exactly 486717968 512-Byte-Blocks) Volume Free Space: 56.4 GB (56438132736 Bytes) (exactly 110230728 512-Byte-Blocks) Device Block Size: 512 Bytes Read-Only Media: No Read-Only Volume: No Ejectable: No Whole: No Internal: Yes Solid State: No
