On 06/15/2015 07:56 AM, Robert Nichols wrote:> On 06/14/2015 10:08 PM, jd1008 wrote: >> >> >> On 06/14/2015 08:58 PM, John R Pierce wrote: >>> On 6/14/2015 6:55 PM, Timothy Murphy wrote: >>>> Maybe I used dd at some point. >>>> Would this keep the same UUID? >>> >>> DD just does a blind block by block copy between two devices or files. >>> >>> >>> >> I thought that uuid had nothing to do with drive content, >> so dd would have (should have had) nothing to do with it. > > You thought wrong. The UUID for a GPT partition is a number that is > recorded in the GPT. The UUID for a filesystem is a number that is > recorded in the filesystem super block. The UUIDs for LVM physical > or logical volumes are numbers recorded in the LVM header. Etc., > etc., etc. When you use dd to copy them, the UUIDs get copied > too, and significant confusion can result. > > Now, the drive itself does have a UUID derived from information > that includes the serial number. But, unless you are referencing > the drive by /dev/disk/by-uuid/*, you are not making use of it. > I've occasionally used /dev/disk/by-id/xxx to select a particular > drive partition that could not be reliably identified in any other > way (encrypted swap partition on a non-GPT drive), but I don't > recall ever using /dev/disk/by-uuid/. >Thanx for the update but what about non-gpt and non lvm partitions? What is used as inp nut to create a universally unique id? (Actually, for an id to be universally unique, one would almost nee knowledge of all existing id's. So, I do not have much credence in this universal uniqueness.
On Mon, 15 Jun 2015, jd1008 wrote:> Thanx for the update > but what about non-gpt and non lvm partitions? > What is used as inp > nut to create a universally unique id? > > (Actually, for an id to be universally unique, one would almost > nee knowledge of all existing id's. > So, I do not have much credence in this universal uniqueness.Sufficiently random gets you there, since you're not connecting billions of filesystems to a single system. If you really want to generate them by hand, feel free, as mkfs.ext4 lets you specify the filesystem UUID. I think you're finding a problem where one does not exist. jh
On 6/15/2015 9:08 AM, jd1008 wrote:> Thanx for the update > but what about non-gpt and non lvm partitions? > What is used as inp > nut to create a universally unique id?The UUID optionally used for mounting has nothing to do with GPT or LVM, its a label in superblock of the FILE system contained in the logical partition or volume. -- john r pierce, recycling bits in santa cruz
On 15.06.2015 18:13, John Hodrien wrote:> On Mon, 15 Jun 2015, jd1008 wrote: > >> Thanx for the update >> but what about non-gpt and non lvm partitions? >> What is used as inp >> nut to create a universally unique id? >> >> (Actually, for an id to be universally unique, one would almost >> nee knowledge of all existing id's. >> So, I do not have much credence in this universal uniqueness. > > Sufficiently random gets you there, since you're not connecting billions of > filesystems to a single system. If you really want to generate them by > hand, > feel free, as mkfs.ext4 lets you specify the filesystem UUID.Or if you are in the situation of the original poster and made a copy using dd use tune2fs -L and -U to modify label and uuid of the copy. Regards, Dennis
On 06/15/2015 11:08 AM, jd1008 wrote:> Thanx for the update > but what about non-gpt and non lvm partitions? > What is used as inp > nut to create a universally unique id?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. -- Bob Nichols "NOSPAM" is really part of my email address. Do NOT delete it.
On Mon, 2015-06-15 at 21:41 -0500, Robert Nichols wrote:> 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.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 I encrypted some of those partitions. The 'blkid' command produces a list of UUIDs for those partitions. A few examples:-> /dev/sda5: LABEL="a5u" UUID="3cbc7570-30b8-4970-a0df-a9a9602770d0" TYPE="ext4" > /dev/sda2: UUID="e954fbaa-dc51-46dc-a352-cceb439080e5" TYPE="crypt_LUKS" > /dev/ram0: UUID="49b98b86-116a-469b-b6de-a157bb0a12dd" TYPE="ext2" > /dev/sda1: LABEL="d6sys" UUID="cd632820-0701-4a6a-b329-6798b6a29966" TYPE="ext3" SEC_TYPE="ext2"-- Regards, Paul. England, EU. England's place is in the European Union.