How to change filesystem UUID (2 same UUID)?
I have a fedora guest OS in VMware. I want to expand /boot partition, so I add another virtual disk to this VM, and try to clone the disk. After dd if=/dev/sda1 of=/dev/sdb1 , blkid report that /dev/sda1 and /dev/sdb1 have same UUID/GUID. It’s weird that there’re 2 same UUIDs in the universe, how to change one of them to another UUID value?
Update 2017-01-25
Subject changed, UUID here means filesystem UUID, not partition UUID. Since it’s filesystem UUID, filesystem specific utils are needed to change the UUID, or use hexeditor to modify raw data on disk (DANGEROUS, not recommended unless you know what you are doing).
It’s not weird at all. When you clone a partition with dd, of course the clone will have the same UUID as the original. The UUID is just metadata of the partition — not some inherent property of a physical disk.
Thank you Andrew, I thought UUID is a calculated value before when a new partition been created. Now I know it’s just a metadata stuff.
10 Answers 10
To generate a random new UUID, one can use:
To actually change the UUID is file system dependent.
Assuming ext-family filesystem
Or if you’re confident uuidgen is going to work:
# tune2fs -U $(uuidgen) /dev/sdb1 Assuming btrfs filesystem
# btrfstune -U $(uuidgen) /dev/sdb1 The UUID is stored in the superblock, so a byte-for-byte copy of the filesystem will have the same UUID.
N.B. this does not work when you have multiple physical devices and their partitions combined within single volume.
if it’s an ext filesystem, or
xfs_admin -U generate /dev/sdb1 if it’s an xfs filesystem.
The reason the second partition has the same UUID is because dd just copies data from one file to another ( dd if=/dev/sda1 of=/dev/sdb1 = cat /dev/sda1 > /dev/sdb1 ); dd doesn’t know what a partition is, or how to generate a UUID, so it just copied all the data as-is, including the UUID, which is stored in the filysystem superblock near the start of the partition.
By the way,
I also think UUID (Universally Unique IDentifier) is a weird name. It should be called PGUID (Possibly Globally Unique IDentifier), or even better, just ARLN (A Reasonably Large Number).
I have backed up one my partitions on /dev/sda6. I get the following error: xfs_admin -U generate /dev/sda6 ERROR: The filesystem has valuable metadata changes in a log which needs to be replayed. Mount the filesystem to replay the log, and unmount it before re-running xfs_admin. If you are unable to mount the filesystem, then use the xfs_repair -L option to destroy the log and attempt a repair. Note that destroying the log may cause corruption — please attempt a mount of the filesystem before doing this.
Well, I would suggest Globally Unique IDentifier (GUID) — «Globally» as in «generally», or «in general» . Oh wait. isn’t this actually its original name.
Besides of ext2 /ext3 / ex4 and xfs, you can also change UUID of the following filesystem or block device or PARTUUID of GPT partition.
Swap
Software RAID (md raid)
For MD RAID, you must stop the RAID first, then update the UUID when re-assembling. So if your RAID is mounted to / , you can’t stop it, you need update UUID in offline mode — use a live CD/USB to do it.
- mdadm —stop $RAID_DEVICE
- mdadm —assemble $RAID_DEVICE —update=uuid —uuid=$NEW_UUID $MEMBER_DEVICES.
- mdadm —stop /dev/md127
- mdadm —assemble /dev/md127 —update=uuid —uuid=2A1D2A1D-2A1D-2A1D-2A1D-2A1D2A1D2A1D /dev/sda2 /dev/sdb2
After UUID been updated, you may need to update grub.cfg ( rd.md.uuid=$NEW_UUID in linux/linuxefi/linux16 command line) and/or fstab and/or mdadm.conf and/or update-initramfs (Debian family) and/or dracut —force (Red Hat family) so that you can boot successfully next time.
LUKS (cryptsetup)
cryptsetup luksUUID —uuid=$NEW_UUID $LUKS_DEVICE
cryptsetup luksUUID —uuid=e0c0e0c0-e0c0-e0c0-e0c0-e0c0e0c0e0c0 ~/encrypted-LUKS.loop
NTFS file system
There’s ntfslabel utility (thanks to ntfs-3g) to change UUID of NTFS file system. See abchk1234’s answer.
In case you wanna change the whole UUID of NTFS file system instead of —new-half-serial , use the —new-serial option.
ntfslabel —new-serial=1122334455667788 /dev/sda3
FAT / exFAT file system
This is another story here, currently there’re no utilities to modify the filesystem UUID of these filesystems (See reichhart’s answer — the mlabel tool), but we can modify raw data on disk to do this.
WARNING, it’s dangerous to modify raw data on disk, and could lost data without careful operation.
Here’s detail steps to modify raw data on disk using hexedit .
- blkid , write down the UUID of filesystem to paper, or remember it. The UUID string of FAT / exFAT looks like 1122-3344 , UUID string of NTFS looks like 1122334455667788 .
- Open partition device using hexedit hexedit
- Press / , enter the UUID in reverse order (if blkid reported 1234-ABCD , then search CDAB3412 ) to search the UUID data on disk.
- Once UUID is located, change them, press F2 to save and exit.
- blkid to verify the UUID.
- Once UUID is modified, you may need to update grub.cfg and/or fstab so that you can boot successfully next time.
- Execute fsck and see a «There are differences between boot sector and its backup» message. In order to solve it, select «1) Copy original to backup», and if you are asked «Perform changes ? (y/n)» you press y .
PARTUUID of GPT partition
A short story: I never thought I will need to touch PARTUUID of GPT partition, until now, when I try to migrate Windows from a small disk to a large disk, Windows failed to boot on the large disk and it can’t even be repaired automatically. The reason is that changing UUID of NTFS file system to the original one isn’t enough for Windows + UEFI, you also need to change the PARTUUID of GPT partition — PARTUUID matter. (After changed PARTUUID to the original one, Windows successfully booted from the large disk.)
There’s already an answer here on askubuntu.com to show how to change PARTUUID of GPT partition using gdisk utility.
The current version of fdisk (2.35.2 in Fedora 32 repositories at the time of editing) from util-linux can do that too in expert mode, in fact, starting from util-linux v2.23, fdisk has been GPT-enabled.
Here’s an example of changing PARTUUID using util-linux fdisk utility:
# truncate -s 200M /tmp/file-as-a.disk # LANG=en_US.UTF-8 fdisk /tmp/file-as-a.disk Welcome to fdisk (util-linux 2.35.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table. Created a new DOS disklabel with disk identifier 0xc0fc8503. Command (m for help): g Created a new GPT disklabel (GUID: 4CD23B97-80C5-BD42-8466-1B9476653A92). Command (m for help): n Partition number (1-128, default 1): First sector (2048-409566, default 2048): Last sector, +/-sectors or +/-size (2048-409566, default 409566): Created a new partition 1 of type 'Linux filesystem' and of size 199 MiB. Command (m for help): i Selected partition 1 Device: /tmp/file-as-a.disk1 Start: 2048 End: 409566 Sectors: 407519 Size: 199M Type: Linux filesystem Type-UUID: 0FC63DAF-8483-4772-8E79-3D69D8477DE4 UUID: 7265D7C3-6277-DE4B-956C-41E3BFFF8E0D Command (m for help): w The partition table has been altered. Syncing disks. # LANG=en_US.UTF-8 fdisk /tmp/file-as-a.disk Welcome to fdisk (util-linux 2.35.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): x Expert command (m for help): m Help (expert commands): GPT i change disk GUID n change partition name u change partition UUID l change table length M enter protective/hybrid MBR A toggle the legacy BIOS bootable flag B toggle the no block IO protocol flag R toggle the required partition flag S toggle the GUID specific bits Generic p print the partition table v verify the partition table d print the raw data of the first sector from the device D print the raw data of the disklabel from the device f fix partitions order m print this menu Save & Exit q quit without saving changes r return to main menu Expert command (m for help): u Selected partition 1 New UUID (in 8-4-4-4-12 format): 11223344-5566-7788-9900-AABBCCDDEEFF Partition UUID changed from 7265D7C3-6277-DE4B-956C-41E3BFFF8E0D to 11223344-5566-7788-9900-AABBCCDDEEFF. Expert command (m for help): w w: unknown command Expert command (m for help): r Command (m for help): w The partition table has been altered. Syncing disks. # losetup --partscan /dev/loop101 /tmp/file-as-a.disk # blkid /dev/loop101* /dev/loop101: PTUUID="4cd23b97-80c5-bd42-8466-1b9476653a92" PTTYPE="gpt" /dev/loop101p1: PARTUUID="11223344-5566-7788-9900-aabbccddeeff" How to change vfat partition UUID?
It might be helpful to know why you want to do this. I don’t know of a tool to do what you want, but there may be other options.
Technically, FAT partitions don’t have UUIDs; they have serial numbers, which several Linux tools and files (such as mount and /etc/fstab ) can use in place of UUIDs. On GPT disks, the partitions that hold FAT filesystems have GUIDs, which (on recent enough Linux distributions) can be referred to as PARTUUIDs in mount and /etc/fstab . Both FAT filesystems and (on GPT disks) the partitions that contain them can also have names, which can also be used by mount or in /etc/fstab . Any of these features might be usable in place of the FAT serial number.
Although I don’t know of a tool to change FAT partitions’ serial numbers, they can be set when the filesystem is created via the -i option to mkdosfs , as in:
mkdosfs -i ABCD1234 /dev/sdc1 This example sets the serial number of /dev/sdc1 to ABCD-1234. If the filesystem is small enough, you could back it up, create a fresh filesystem with the desired serial number, and restore it. If you’re trying to set the serial number as part of a disk or installation setup script, setting it via mkdosfs might be all you need.
You can change the partition’s GUID with gdisk or sgdisk . Using the latter, you’d do the job via the -u option, as in:
sgdisk -u 1:BC87D91A-02F3-4C52-87CD-536A3DF2A074 /dev/sdc This example sets the GUID of /dev/sdc1 to BC87D91A-02F3-4C52-87CD-536A3DF2A074. (Note that -u takes a colon-delimited set of options, the first of which is the partition number and the second of which is the GUID value. The device filename for the whole-disk device [not the partition] is the final option.)
Depending on your needs, one of these approaches may work. Moving broader afield, you can set the filesystem’s label with the dosfslabel tool; or you can change a GPT partition’s name with sgdisk ‘s -c option, which works much like -u , but takes a name rather than a GUID.