Duplicate UUIDs, findmnt, /dev/disk/by-uuid

Duplicate UUIDs, findmnt, /dev/disk/by-uuid

[Marcin Szewczyk]

Hi,

I have a system with most of the files on one disk. Sometimes an
additional storage is added by inserting another disk. There is an
application included in this system to setup a disk for that additional
storage. It lets a user choose any disk from the pool of not mounted
drives.

The system has been cloned (with dd) to many disks inserted to many
machines. From time to time someone inserts an additional disk which has
been previously used as the system disk. Then there are two filesystems
with same UUIDs inserted to one machine.

The mentioned application uses findmnt to blacklist drives with any
partitions mounted.

Findmnt seems to use links from /dev/disk/by-uuid. There is only one
link for every UUID and it leads to the last detected disk with that
UUID. It causes my application to let the user choose the mounted root
filesystem.

As a workaround I use /proc/self/mountinfo as it gives me major and
minor numbers.

My question is: is there a way to force findmnt to use major and minor
numbers from /proc/self/mountinfo to identify disks/partitions?


Example (using only one disk):
# findmnt -cnko SOURCE /media/sdd
/dev/sdd2
# cat /proc/self/mountinfo | grep sdd
31 19 8:49 / /media/sdd rw,relatime - ext4 /dev/disk/by-uuid/a1d15a89-470a-4a1e-a763-20d4b404d507 rw,user_xattr,barrier=1,data=ordered
# blkid | grep sdd
/dev/sdd1: UUID="a1d15a89-470a-4a1e-a763-20d4b404d507" TYPE="ext4" 
/dev/sdd2: UUID="a1d15a89-470a-4a1e-a763-20d4b404d507" TYPE="ext4"
# ls -la /dev/sdd*
brw-rw---T 1 root floppy 8, 48 Apr 23 16:13 /dev/sdd
brw-rw---T 1 root floppy 8, 49 Apr 23 16:13 /dev/sdd1
brw-rw---T 1 root floppy 8, 50 Apr 23 16:20 /dev/sdd2


-- 
Marcin Szewczyk                       http://wodny.org
mailto:Marcin.Szewczyk@wodny.borg  <- remove b / usuń b
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Re: Duplicate UUIDs, findmnt, /dev/disk/by-uuid

[Ted Ts'o]

On Mon, Apr 23, 2012 at 05:41:06PM +0200, Marcin Szewczyk wrote:
> 
> The system has been cloned (with dd) to many disks inserted to many
> machines. From time to time someone inserts an additional disk which has
> been previously used as the system disk. Then there are two filesystems
> with same UUIDs inserted to one machine.

This probably won't help you that much now, but best practice for
ext[234] file systems is after you clone them using dd, you should run
the command "tune2fs -U random /dev/sdXX" to reset the UUID to a new
random value.  For XFS, the command is "xfs_admin -U generate /dev/sdXX".
For ntfs, the advanced utilities have a --new-serial option to ntfslabel.

It's *always* a good idea to make sure that the UUID is reset after
cloning a file system, to avoid this sort of problem.

Regards,

					- Ted

Re: Duplicate UUIDs, findmnt, /dev/disk/by-uuid

[Karel Zak]

On Mon, Apr 23, 2012 at 05:41:06PM +0200, Marcin Szewczyk wrote:
> As a workaround I use /proc/self/mountinfo as it gives me major and
> minor numbers.
> 
> My question is: is there a way to force findmnt to use major and minor
> numbers from /proc/self/mountinfo to identify disks/partitions?

 Implemented (in upstream tree).

 $ findmnt 8:1
 TARGET    SOURCE    FSTYPE OPTIONS
 /boot/efi /dev/sda1 vfat   rw,relatime,fmask=0077,dmask=0077,codepage=cp437,ioch


 (or with "--source 8:1" option to make it more explicit)

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: Duplicate UUIDs, findmnt, /dev/disk/by-uuid

[Marcin Szewczyk]

On Wed, Apr 25, 2012 at 09:56:28AM +0200, Karel Zak wrote:
>  Implemented (in upstream tree).
> 
>  $ findmnt 8:1
>  TARGET    SOURCE    FSTYPE OPTIONS
>  /boot/efi /dev/sda1 vfat   rw,relatime,fmask=0077,dmask=0077,codepage=cp437,ioch
> 
> 
>  (or with "--source 8:1" option to make it more explicit)

BTW, I've completely missed the MAJ:MIN functionality at first. I've
filed a bug report[1] to Debian mount package to mention the MAJ:MIN
column.

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=670273

-- 
Marcin Szewczyk                       http://wodny.org
mailto:Marcin.Szewczyk@wodny.borg  <- remove b / usuń b
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