Changing the UUID of a FAT32 or NTFS Partition

[clubsoda]

I'm used to finding the answers to all my technical questions with a couple of 'net searches but information in this area seems a bit scarce.

The typical scenario is that a partition has been backed up using a cloning tool like parted, then various problems appear due to the duplicated UUID. The accepted solution is to alter the volume label on the backup partition using mlabel [mtools] and then edit /etc/fstab to have the backup partition identified using LABEL="WinWhatever" instead of UUID=89C9589FC4162F5. That's not necessarily the end of the story though. A live CD or reinstaller will again trip over the duplicate UUID.

A more robust solution is to alter the UUID on the backup partition and create a record of the original UUID at the same time, in case the master partition crashes and is unrecoverable. First let's see what we've got:-

sudo blkid

Make a note of the partition number X of the backup partition. Use that number instead of X in all the comands below.

Now let's grab the superblock:-

sudo dd if=/dev/sdaX of=~/superblockX bs=512 count=1

And edit it using hexeditor [ncurses-hexedit]:-

sudo hexeditor ~/superblockX

The UUID shown by blkid earlier will match the volume serial number which you should see at 0x43-0x46 for VFAT or 0x48-0x4f for NTFS. Change it somehow and save.

[Optional sanity check: "ls -l ~/superblockX" The file should still be exactly 512 bytes].

Copy the modified file back to the superblock. I don't need to mention how risky this part is. Be sure you know what you're doing.

sudo dd if=~/superblockX of=/dev/sdaX bs=512 count=1

Next edit /etc/fstab with a line identifying the backup partition via its new UUID. You might want to add noauto to the options if you don't want it mounted automatically all the time. Finally, I suggest mounting the backup partition and adding a tag file to its root directory. The file name should indicate the original UUID prior to editing, eg. 540C-0199.vol, as this will be needed if the master partition ever crashes catastrophically or needs to be restored.

I hope this process will all be automated one day. See this bug report.

Please post back if you spot errors or if there are just better ways to do the above. I haven't tested this on an NTFS partition yet.

References:
How FAT32 volume serial numbers are calculated.
Some info on NTFS.

[say2sky]

Thank you for this very useful howto.

I also have partition with xfs, ext3, can I use the same solution as this one. is there any other thing need to make change?

Anyway this is a good solution.

[clubsoda]

I'm sure you could use this method on xfs or ext3 if you're feeling adventurous. Thankfully, those file systems are better supported so no need for open-block surgery. Have a look at xfs_admin [xfstools] and tune2fs.

[dcstar]

This should patch the NTFS UUID with 8 random bytes (substitute the obvious with your actual NTFS partition designation, and all those spaces are required):

sudo dd if=/dev/urandom bs=80 count=1 | xxd -l 80 -c 8 | tail -1 | xxd -r - /dev/sd-NTFS-Partition

[GMHilltop]

This should patch the NTFS UUID with 8 random bytes (substitute the obvious with your actual NTFS partition designation, and all those spaces are required):

sudo dd if=/dev/urandom bs=80 count=1 | xxd -l 80 -c 8 | tail -1 | xxd -r - /dev/sd-NTFS-Partition

Can you clarify the code for me please? Ones ( 1 ) and L's ( l ) can look very similar.

Also, could you clarify the ".... sd-NTFS-Partition" part? is that supposed to be:
".... sdx-NTFS-Partition" where 'x' is the partition you'd like the uuid change on?

Are there any other parts of the code that we should be inserting the 'appropriate' value that is currently holding an 'x' place holder (ie the xxd part of the code)?

Thanks again for the help

[GMHilltop]

Ok, I gave this a try from a Live CD 10.04.1 LTS

I imaged a windows 7 OS to the first and 2nd partition of the hard drive and checked that they both have the same UUID by typing in ===> sudo blkid

I assumed that:
the count=1 was a "One"
--- and that the xxd -l was an "L"
--- and that the /dev/sd-NTFS-Partition was supposed to be .... /dev/sda1-NTFS-Partition (assuming that it was the 1st partition on the drive that I was trying to change the UUID on.

When I ran it I got this message:
xxd: /dev/sda1-NTFS-Partition: Permission denied
1+0 records in
1+0 records out
80 bytes (80 B) copied, 0.000107521 s, 744 kB/s

Does anyone here have a suggestion as to how to make this work as it would be VERY VERY handy to be able to change the UUID with a single line like this!

[dcstar]

Ok, I gave this a try from a Live CD 10.04.1 LTS

I imaged a windows 7 OS to the first and 2nd partition of the hard drive and checked that they both have the same UUID by typing in ===> sudo blkid

I assumed that:
the count=1 was a "One"
--- and that the xxd -l was an "L"
--- and that the /dev/sd-NTFS-Partition was supposed to be .... /dev/sda1-NTFS-Partition (assuming that it was the 1st partition on the drive that I was trying to change the UUID on.

When I ran it I got this message:
xxd: /dev/sda1-NTFS-Partition: Permission denied
1+0 records in
1+0 records out
80 bytes (80 B) copied, 0.000107521 s, 744 kB/s

Does anyone here have a suggestion as to how to make this work as it would be VERY VERY handy to be able to change the UUID with a single line like this!

Why do I have to explain the bloody obvious?

I do not know what YOUR NTFS partition is, REPLACE that with the actual designation of your NTFS partition.

If you are not able to identify what partition you are supposed to be working on that I strongly advise you not to use commands like this until your Linux skills significantly improve.

[GMHilltop]

Why do I have to explain the bloody obvious?

Because OBVIOUSLY there was room in YOUR POST for 'misinterpretation'.

I do not know what YOUR NTFS partition is, REPLACE that with the actual designation of your NTFS partition.

Yeah, that part too was "bloody obvious", and counter productive.

For future reference when giving advice, most times, an example (just to be absolutely clear) goes a long long way towards helping others completely understand what it is you are saying.

That too should have been "bloody obvious" to you.
You choose to ignore that however (and the other OBVIOUS questions), and instead decided to be snippy.

If you are not able to identify what partition you are supposed to be working on ...

I would have thought:
"... /dev/sda1 .... (assuming that it was the 1st partition on the drive that I was trying to change the UUID on."
was "bloody obvious" that I knew which partition it was that I was trying to change the UUID on. No? >>>>sda1<<<<

. . . that I strongly advise you not to use commands like this until your Linux skills significantly improve.

Completely irrelevant, totally useless, and utterly pompous advise.
Seriously, how is anything like that helpful to anyone. WOW!
I think that this community and forum have been amazing at helping people learn the "bloody obvious" without being condescending.

dcstar, I strongly advise that you be "crystal clear" with your code by "giving examples", AND when questions are asked about the code that you have given, that you answer ALL of them (even if to you it is 'bloody obvious') in order to help others "improve their Linux skills significantly".

Your last post does linux, ubuntu, and this forum a huge disservice IMHO.

===========

Now that those pleasantries are out of the way,
and,
after looking at it again and giving my head a smack for missing the bloody obvious,
AND at the risk of misunderstanding dcstar again,
I'll attempt to answer my queries for the benefit of others

The Code dcstar posted was:

sudo dd if=/dev/urandom bs=80 count=1 | xxd -l 80 -c 8 | tail -1 | xxd -r - /dev/sd-NTFS-Partition

I, by mistake left the "-NTFS-Partition" in when I ran the command. Yeah that was kinda dumb, but if I made the mistake it's possible others could too.

I'd like, for the benefit of others, to provide an example of what I think dcstar was trying to say (please dcstar correct me if I have still got it wrong):

If I was trying to change the UUID of the first partition on the first hard drive the code should have been this:

sudo dd if=/dev/urandom bs=80 count=1 | xxd -l 80 -c 8 | tail -1 | xxd -r - /dev/sda1

I had: ...... /dev/sda1-NTFS-Partition mistakenly at the end of the code.

I have seen some posts say things like: replace xx with ..... (some value where the x's are representing something else)
hence my query about the 'xxd' part of the code.

I know, I know - dcstar didn't say anything about changing anything with the "x's" - clearly my Linux (& reading comprehension) skills need improving, but that is why I (and many others) are here , and it is not going to stop me from tinkering while I learn .

also, I believe the -l in the xxd -l is a lower case "L"
the count=1 is a "ONE" ===>not sure if that was supposed to be "bloody obvious" . . . 'count=1'
and in 'tail -1' . . . that I am pretty sure is a "ONE"

To Repeat dcstar's comment - ... all the spaces are required.

Hopefully I have this right, and I haven't mislead anyone while trying to clear this up.

[GMHilltop]

Well I finally had an opportunity to sit down and tinker a little with this again.

The Code that I used in terminal was:

sudo dd if=/dev/urandom bs=80 count=1 | xxd -l 80 -c 8 | tail -1 | xxd -r - /dev/sda1

Now the result is this:

xxd: /dev/sda1: Permission denied
1+0 records in
1+0 records out
80 bytes (80 B) copied, 4.9104e-05 s, 1.6 MB/s
ubuntu@ubuntu:~$

Can anyone clarify for me what it is that I am missing with this code?

Thanks again for the help.

[GMHilltop]

Ok, THIS I got to work for me - Hopefully it helps others as well.

First credit where credit is due - I got the help I was looking for here:

Changing / Modifying an NTFS partitions UUID using dd

Thank You very much to Simon Williams for taking the time to respond (See the comments to Adam's original post there). I hope everyone here finds this as useful.

Here is The Code used:

sudo dd if=/dev/urandom of=/dev/[ntfspartition] bs=8 count=1 seek=9

!!!!!!!!!!!!!!! WARNING WARNING WARNING !!!!!!!!!!!
For [ntfspartition] YOU MUST make sure you Identify the PROPER partition!!
ie: sda1 or sda2 or sdb1 or sdb2 or sdc1 or sdc2 etc etc etc.
DO NOT put sda in there or you will SCREW your MBR !
Also you will want to run: sudo blkid to make SURE you are modifying the proper partition.
DO NOT miss any part of the code above or you'll risk modifying more than just the UUID
also posted at the above link with regard to the above code:
Be warned that you can cause data loss ON ANY DISK CONNECTED TO YOUR MACHINE if you specify the wrong disk or partition, or if the partition you specify turns out to not be the one you were expecting. Disks of the "new" form /dev/sda (rather than the old /dev/hda, etc) have unpredictable ordering. Running this on a non-NTFS partition, or worse, the entire disk (e.g. /dev/sda rather than /dev/sda1) will mess things up very badly. YOU HAVE BEEN WARNED.
!!!!!!!!!!!!!!! END OF WARNING !!!!!!!!!!!!!!!!

as an example of the the code to be used --- if I wanted to modify the UUID of the 1st partition of the first hard drive IN MY SYSTEM this is what I would type:

sudo dd if=/dev/urandom of=/dev/sda1 bs=8 count=1 seek=9

to do the 2nd partition of the first hard drive it would be:

sudo dd if=/dev/urandom of=/dev/sda2 bs=8 count=1 seek=9

(Again - best verify what the system sees IN YOUR SYSTEM by typing in Sudo blkid)

Simon Williams gives a very nice breakdown as to what each piece of the code does for those who are interested (Again - it is in the comments to the original post there).
I think it is the 11th comment that starts off with "dd explained"
Comment 14 by Simon Williams that starts off with "written by Simon Williams, October 13, 2010
Yey, now that I can login again... :S "
gives even further detail to this part of the code:
/dev/urandom

Again Thanks again to Simon Williams for the assistance. He was very professional and courteous!