[CentOS] Two partitions with samd UUID??

[James Hogarth]

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 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.

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.

> > > Non-GPT partitions do not have a UUID. The _content_ (filesystem,
> > > LVM physical volume, non-encrypted swap space, etc.) of such a
> > > partition could have a UUID, but the partition itself does not.
>
> When I think I am mounting a M$ DOS partition, am I mounting a real
> partition or merely 'the file system' within that partition ?  Some may
> think one can't have one without the other.
>
>

Of course you can have a partition or filesystem without the other. This is
how raw devices work and you can mkfs a block device with no partitions.

When you mount something you mount the filesystem.