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.