On 06/16/2015 06:43 AM, James Hogarth wrote: > On 16 Jun 2015 12:12, "Always Learning" <centos at u64.u22.net> wrote: >> >> >> On Tue, 2015-06-16 at 11:30 +0100, John Hodrien wrote: >>> On Tue, 16 Jun 2015, Always Learning wrote: >>> >>>> ON Centos 5, using GPARTED I created partitions for filing systems > ext3 >>>> and ext4. 4 primary and unlimited (except by space) extended > partitions. >>>> That suggests those partitions are not GPT but old fashioned M$DOS >>> >>> If it is old fashioned MSDOS, you can have four total primary and > extended, >>> not four primary plus extended. An extended partition then provides a >>> container for further logical partitions. >> >> Yes you are correct. Maximum 4 primary or maximum 3 primary and 1 >> extended which is then sub-divided into more partitions. >> >>> LUKS provides a UUID, so being encrypted isn't a barrier to having a > UUID. >> >> But my point was M$ DOS partitions, not being GPT partitions, can have >> UUIDs. The original poster appeared to suggest that was not possible. He >> wrote >> > > Those were filesystem UUIDs not partition UUIDs ... LUKS physical volume UUIDs, actually. When you create a LUKS logical volume within that PV, it also has a UUID, and a filesystem within that LUKS LV will have its own UUID. These are all part of the partition's _content_. A GPT partition has its own UUID, independent of the partition's content. An MSDOS partition does not. > LUKS has its own header similar to ext4, lvm, etc headers which has a UUID > in it. > > This UUID being associated with the LUKS header indicates it is not a > partition UUID. > > A dd of this (or lvm snapshot) to another partition will keep the same UUID. Indeed. If your version of cryptsetup is new enough (supports the "--header" option), try doing the luksFormat operation with a detached header. Now you will find that your LUKS partition no longer has a UUID. > A partition UUID within a GPT table would not be persisted in this manner, > and msdos labeled disks have no concept of this to begin with. -- Bob Nichols "NOSPAM" is really part of my email address. Do NOT delete it.