CSUNIQUE(8) System Manager's Manual CSUNIQUE(8)

csunique — modify the UUIDs of CoreStorage metadata objects

csunique [-v | --verbose] [-n | --dry-run] [-I | --include include] [-X | --exclude exclude] device ...

The csunique utility can rewrite CoreStorage logical volume group metadata, changing object UUIDs. All CoreStorage objects are uniquely identified by UUIDs. This can be useful when copying an initial "canned image" onto multiple machines to establish these as independent volumes.

The device parameter(s) should be path(s) to the "raw" (character special) disk device(s) such as /dev/rdisk1s1 that constitute the CoreStorage logical volume group. If you specify a "non-raw" (block special) path such as /dev/disk1s1, or just the disk name such as disk1s1, it will automatically be converted to the corresponding raw disk device (/dev/rdisk1s1).

The options are as follows:

Output verbose progress information of each step and the UUID re-mappings.
Operates in "dry run" mode; no changes are made to the on-disk data.
Specifies an additional class of UUID objects that should be modified.
Specifies a class of UUID objects that should not be modified. By default all UUIDs will be changed.

The classes of CoreStorage UUID objects that can be included or excluded from modification by csunique are indicated using the following characters:

f
logical volume family (LVF)
g
logical volume group (LVG)
l
logical volume (LV)
p
physical volume (PV)
w
MLV wipekey

csunique processes/transforms the CoreStorage metadata in a number of steps:

  1. Firstly, an initial fsck_cs is performed to ensure the source structure is consistent;
  2. If the LVG is currently live and mounted by the kext it is temporarily "frozen";
  3. If the disk partitions are of type Apple_CoreStorage then they are switched offline (which dissociates the kext from the old metadata);
  4. The CoreStorage metadata is locally parsed and loaded;
  5. All object UUIDs are located, and new UUIDs generated for classes as set by the -I and -X options;
  6. UUIDs are re-written to disk;
  7. A post-modification fsck_cs is performed to ensure the final structure is consistent;
  8. Finally, any disk partitions taken offline are restored to Apple_CoreStorage (which will reload the kext with the new UUID metadata).

The csunique utility exits with 0 if the CoreStorage logical volume group was modified as directed, and with >0 if it was unable to do so. Any error message is written to stderr.

csunique cannot modify the LVF UUID if there are any encrypted LVs inside it. Any mounted LVs must be manually unmounted before invocation.

The csunique utility first appeared in OS X 10.8.1.

September 25, 2012 OS X